Publications by year
In Press
Caves E, Troscianko J, Kelley L (In Press). A customizable, low-cost optomotor apparatus: a powerful tool for behaviourally measuring visual capability. Methods in Ecology and Evolution
Troscianko J, Briolat ES, Gaston KJ, Bennie J, Rosenfeld EJ (In Press). Artificial nighttime lighting impacts visual ecology links between flowers, pollinators and predators. Nature Communications
Price N, Green S, Troscianko J, Tregenza T, Stevens M (In Press). Background matching and disruptive coloration as habitat-specific strategies for camouflage. Scientific Reports
Heathcote R, Darden S, Troscianko J, Lawson MRM, Brown AM, Laker PR, Naisbett-Jones LC, MacGregor HEA, Ramnarine I, Croft DP, et al (In Press). Dynamic eye colour as an honest signal of aggression. Current Biology
Stevens M, Broderick AC, Godley BJ, Lown AE, Troscianko J, Weber N, Weber SB (In Press). Phenotype-Environment Matching in Sand Fleas. Biology Letters
Dalbosco Dell’Aglio D, Troscianko J, McMillan WO, Stevens M, Jiggins CD (In Press). The appearance of mimetic Heliconius butterflies to predators and conspecifics. Evolution
Kelley L, Troscianko J (In Press). The evolution of patterning during movement in a large-scale citizen science game. Proceedings of the Royal Society B: Biological Sciences
2023
Troscianko J, Osorio D (2023). A model of colour appearance based on efficient coding of natural images.
PLoS Comput Biol,
19(6).
Abstract:
A model of colour appearance based on efficient coding of natural images.
An object's colour, brightness and pattern are all influenced by its surroundings, and a number of visual phenomena and "illusions" have been discovered that highlight these often dramatic effects. Explanations for these phenomena range from low-level neural mechanisms to high-level processes that incorporate contextual information or prior knowledge. Importantly, few of these phenomena can currently be accounted for in quantitative models of colour appearance. Here we ask to what extent colour appearance is predicted by a model based on the principle of coding efficiency. The model assumes that the image is encoded by noisy spatio-chromatic filters at one octave separations, which are either circularly symmetrical or oriented. Each spatial band's lower threshold is set by the contrast sensitivity function, and the dynamic range of the band is a fixed multiple of this threshold, above which the response saturates. Filter outputs are then reweighted to give equal power in each channel for natural images. We demonstrate that the model fits human behavioural performance in psychophysics experiments, and also primate retinal ganglion responses. Next, we systematically test the model's ability to qualitatively predict over 50 brightness and colour phenomena, with almost complete success. This implies that much of colour appearance is potentially attributable to simple mechanisms evolved for efficient coding of natural images, and is a well-founded basis for modelling the vision of humans and other animals.
Abstract.
Author URL.
Bullough K, Gaston KJ, Troscianko J (2023). Artificial light at night causes conflicting behavioural and morphological defence responses in a marine isopod.
Proc Biol Sci,
290(2000).
Abstract:
Artificial light at night causes conflicting behavioural and morphological defence responses in a marine isopod.
Encroachment of artificial light at night (ALAN) into natural habitats is increasingly recognized as a major source of anthropogenic disturbance. Research focussed on variation in the intensity and spectrum of ALAN emissions has established physiological, behavioural and population-level effects across plants and animals. However, little attention has been paid to the structural aspect of this light, nor how combined morphological and behavioural anti-predator adaptations are affected. We investigated how lighting structure, background reflectance and the three-dimensional properties of the environment combined to affect anti-predator defences in the marine isopod Ligia oceanica. Experimental trials monitored behavioural responses including movement and background choice, and also colour change, a widespread morphological anti-predator mechanism little considered in relation to ALAN exposure. We found that behavioural responses of isopods to ALAN were consistent with classic risk-aversion strategies, being particularly exaggerated under diffuse lighting. However, this behaviour was disconnected from optimal morphological strategies, as diffuse light caused isopods to become lighter coloured while seeking out darker backgrounds. Our work highlights the potential for the structure of natural and artificial light to play a key role in behavioural and morphological processes likely to affect anti-predator adaptations, survival, and ultimately wider ecological effects.
Abstract.
Author URL.
Jolkkonen J, Gaston KJ, Troscianko J (2023). Artificial lighting affects the landscape of fear in a widely distributed shorebird.
Communications Biology,
6(1).
Abstract:
Artificial lighting affects the landscape of fear in a widely distributed shorebird
AbstractFear influences almost all aspects of a prey species’ behaviour, such as its foraging and movement, and has the potential to cause trophic cascades. The superior low-light vision of many predators means that perceived predation risk in prey is likely to be affected by light levels. The widespread and increasing intensity of artificial light at night is therefore likely to interfere with this nocturnal visual arms race with unknown behavioural and ecological consequences. Here we test how the fear of predation perceived by wintering Eurasian curlew foraging on tidal flats is influenced by lighting. We quantified flight initiation distance (FID) of individuals under varying levels of natural and artificial illumination. Our results demonstrate that FID is significantly and substantially reduced at low light levels and increases under higher intensity illumination, with artificial light sources having a greater influence than natural sources. Contrary to the sensory-limitation hypothesis, the curlews’ unwillingness to take flight in low-light appears to reflect the risks posed by low-light flight, and a desire to remain on valuable foraging grounds. These findings demonstrate how artificial light can shape the landscape of fear, and how this interacts with optimal foraging decisions, and the costs of taking flight.
Abstract.
Dixit T, Choi GPT, Al-Mosleh S, Lund J, Troscianko J, Moya C, Mahadevan L, Spottiswoode CN (2023). Combined measures of mimetic fidelity explain imperfect mimicry in a brood parasite-host system.
Biol Lett,
19(2).
Abstract:
Combined measures of mimetic fidelity explain imperfect mimicry in a brood parasite-host system.
The persistence of imperfect mimicry in nature presents a challenge to mimicry theory. Some hypotheses for the existence of imperfect mimicry make differing predictions depending on how mimetic fidelity is measured. Here, we measure mimetic fidelity in a brood parasite-host system using both trait-based and response-based measures of mimetic fidelity. Cuckoo finches Anomalospiza imberbis lay imperfectly mimetic eggs that lack the fine scribbling characteristic of eggs of the tawny-flanked prinia Prinia subflava, a common host species. A trait-based discriminant analysis based on Minkowski functionals-that use geometric and topological morphometric methods related to egg pattern shape and coverage-reflects this consistent difference between host and parasite eggs. These methods could be applied to quantify other phenotypes including stripes and waved patterns. Furthermore, by painting scribbles onto cuckoo finch eggs and testing their rate of rejection compared to control eggs (i.e. a response-based approach to quantify mimetic fidelity), we show that prinias do not discriminate between eggs based on the absence of scribbles. Overall, our results support relaxed selection on cuckoo finches to mimic scribbles, since prinias do not respond differently to eggs with and without scribbles, despite the existence of this consistent trait difference.
Abstract.
Author URL.
Hancock GRA, Grayshon L, Burrell R, Cuthill I, Hoodless A, Troscianko J (2023). Habitat geometry rather than visual acuity limits the visibility of a ground-nesting bird's clutch to terrestrial predators.
ECOLOGY AND EVOLUTION,
13(9).
Author URL.
Hancock G, Grayshon L, Burrell R, Hoodless A, Cuthill I, Troscianko J (2023). Habitat geometry rather than visual acuity limits the visibility of a ground-nesting bird's clutch to terrestrial predators.
Troscianko J (2023). OSpRad: an open-source, low-cost, high-sensitivity spectroradiometer.
J Exp Biol,
226(13).
Abstract:
OSpRad: an open-source, low-cost, high-sensitivity spectroradiometer.
Spectroradiometry is a vital tool in a wide range of biological, physical, astronomical and medical fields, yet its cost and accessibility are frequent barriers to use. Research into the effects of artificial light at night (ALAN) further compounds these difficulties with requirements for sensitivity to extremely low light levels across the ultraviolet to human-visible spectrum. Here, I present an open-source spectroradiometry (OSpRad) system that meets these design challenges. The system utilises an affordable miniature spectrometer chip (Hamamatsu C12880MA), combined with an automated shutter and cosine-corrector, microprocessor controller, and graphical user interface 'app' that can be used with smartphones or desktop computers. The system has high ultraviolet sensitivity and can measure spectral radiance at 0.001
cd
m-2 and irradiance at 0.005 lx, covering the vast majority of real-world night-time light levels. The OSpRad system's low cost and high sensitivity make it well suited to a range of spectrometry and ALAN research.
Abstract.
Author URL.
Kelley JL, Jessop A-L, Kelley LA, Troscianko J (2023). The role of pictorial cues and contrast for camouflage.
Evolutionary EcologyAbstract:
The role of pictorial cues and contrast for camouflage
AbstractShadows that are produced across the surface of an object (self-shadows) are potentially an important source of information for visual systems. Animal patterns may exploit this principle for camouflage, using pictorial cues to produce false depth information that manipulates the viewer’s detection/recognition processes. However, pictorial cues could also facilitate camouflage by matching the contrast (e.g. due to shadows) of 3D backgrounds. Aside from studies of countershading (patterning that may conceal depth information), the role of self-shadows in camouflage patterns remains unclear. Here we investigated whether pictorial cues (self-shadows) increase the survival probability of moth-like prey presented to free-living wild bird predators relative to targets without these cues. We manipulated the presence of self-shadows by adjusting the illumination conditions to produce patterned targets under directional lighting (lit from above or from below; self-shadows present) or diffuse lighting (no self-shadows). We used non-patterned targets (uniform colour) as controls. We manipulated the direction of illumination because it has been linked with depth perception in birds; objects lit from above may appear convex while those lit from below can appear concave. As shadows influence contrast, which also determines detectability, we photographed the targets in situ over the observation period, allowing us to evaluate the effect of visual metrics on survival. We found some evidence that patterned targets without self-shadows had a lower probability of survival than patterned targets with self-shadows and targets with uniform colour. Surprisingly, none of the visual metrics explained variation in survival probability. However, predators increased their foraging efficiency over time, suggesting that predator learning may have overridden the benefits afforded by camouflaging coloration.
Abstract.
2022
Troscianko J, Osorio D (2022). A model of colour appearance based on efficient coding of natural images.
Yorzinski JL, Troscianko J, Briolat E, Schapiro SJ, Whitham W (2022). A songbird can detect the eyes of conspecifics under daylight and artificial nighttime lighting. Environmental Pollution, 313, 120000-120000.
Hancock GRA, Troscianko J (2022). CamoEvo: an open access toolbox for artificial camouflage evolution experiments.
Evolution,
76(5), 870-882.
Abstract:
CamoEvo: an open access toolbox for artificial camouflage evolution experiments.
Camouflage research has long shaped our understanding of evolution by natural selection, and elucidating the mechanisms by which camouflage operates remains a key question in visual ecology. However, the vast diversity of color patterns found in animals and their backgrounds, combined with the scope for complex interactions with receiver vision, presents a fundamental challenge for investigating optimal camouflage strategies. Genetic algorithms (GAs) have provided a potential method for accounting for these interactions, but with limited accessibility. Here, we present CamoEvo, an open-access toolbox for investigating camouflage pattern optimization by using tailored GAs, animal and egg maculation theory, and artificial predation experiments. This system allows for camouflage evolution within the span of just 10-30 generations (∼1-2 min per generation), producing patterns that are both significantly harder to detect and that are optimized to their background. CamoEvo was built in ImageJ to allow for integration with an array of existing open access camouflage analysis tools. We provide guides for editing and adjusting the predation experiment and GA as well as an example experiment. The speed and flexibility of this toolbox makes it adaptable for a wide range of computer-based phenotype optimization experiments.
Abstract.
Author URL.
Whitham W, Schapiro SJ, Troscianko J, Yorzinski JL (2022). Chimpanzee (Pan troglodytes) gaze is conspicuous at ecologically-relevant distances.
Sci Rep,
12(1).
Abstract:
Chimpanzee (Pan troglodytes) gaze is conspicuous at ecologically-relevant distances.
Chimpanzee (Pan troglodytes) sclera appear much darker than the white sclera of human eyes, to such a degree that the direction of chimpanzee gaze may be concealed from conspecifics. Recent debate surrounding this topic has produced mixed results, with some evidence suggesting that (1) primate gaze is indeed concealed from their conspecifics, and (2) gaze colouration is among the suite of traits that distinguish uniquely social and cooperative humans from other primates (the cooperative eye hypothesis). Using a visual modelling approach that properly accounts for specific-specific vision, we reexamined this topic to estimate the extent to which chimpanzee eye coloration is discriminable. We photographed the faces of captive chimpanzees and quantified the discriminability of their pupil, iris, sclera, and surrounding skin. We considered biases of cameras, lighting conditions, and commercial photography software along with primate visual acuity, colour sensitivity, and discrimination ability. Our visual modeling of chimpanzee eye coloration suggests that chimpanzee gaze is visible to conspecifics at a range of distances (within approximately 10 m) appropriate for many species-typical behaviours. We also found that chimpanzee gaze is discriminable to the visual system of primates that chimpanzees prey upon, Colobus monkeys. Chimpanzee sclera colour does not effectively conceal gaze, and we discuss this result with regard to the cooperative eye hypothesis, the evolution of primate eye colouration, and methodological best practices for future primate visual ecology research.
Abstract.
Author URL.
Sulc M, Hughes AE, Mari L, Troscianko J, Tomasek O, Albrecht T, Jelinek V (2022). Nest sanitation as an effective defence against brood parasitism.
ANIMAL COGNITION,
25(4), 991-1002.
Author URL.
Troscianko J (2022). OSpRad; an open-source, low-cost, high-sensitivity spectroradiometer.
Yong L, Croft DP, Troscianko J, Ramnarine IW, Wilson AJ (2022). Sensory-based quantification of male colour patterns in Trinidadian guppies reveals no support for parallel phenotypic evolution in multivariate trait space.
Mol Ecol,
31(5), 1337-1357.
Abstract:
Sensory-based quantification of male colour patterns in Trinidadian guppies reveals no support for parallel phenotypic evolution in multivariate trait space.
Parallel evolution, in which independent populations evolve along similar phenotypic trajectories, offers insights into the repeatability of adaptive evolution. Here, we revisit a classic example of parallelism, that of repeated evolution of brighter males in the Trinidadian guppy (Poecilia reticulata). In guppies, colonisation of low predation habitats is associated with emergence of 'more colourful' phenotypes since predator-induced viability selection for crypsis weakens while sexual selection by female preference for conspicuousness remains strong. Our study differs from previous investigations in three respects. First, we adopted a multivariate phenotyping approach to characterise parallelism in multitrait space. Second, we used ecologically-relevant colour traits defined by the visual systems of the two selective agents (i.e. guppy, predatory cichlid). Third, we estimated population genetic structure to test for adaptive (parallel) evolution against a model of neutral phenotypic divergence. We find strong phenotypic differentiation that is inconsistent with a neutral model but very limited support for the predicted pattern of greater conspicuousness at low predation. Effects of predation regime on each trait were in the expected direction, but weak, largely nonsignificant, and explained little among-population variation. In multitrait space, phenotypic trajectories of lineages colonising low from high predation regimes were not parallel. Our results are consistent with reduced predation risk facilitating adaptive differentiation, potentially by female choice, but suggest that this proceeds in independent directions of multitrait space across lineages. Pool-sequencing data also revealed SNPs showing greater differentiation than expected under neutrality, among which some are found in genes contributing to colour pattern variation, presenting opportunities for future genetic study.
Abstract.
Author URL.
Whitham W, Schapiro SJ, Troscianko J, Yorzinski JL (2022). The gaze of a social monkey is perceptible to conspecifics and predators but not prey.
Proc Biol Sci,
289(1976).
Abstract:
The gaze of a social monkey is perceptible to conspecifics and predators but not prey.
Eye gaze is an important source of information for animals, implicated in communication, cooperation, hunting and antipredator behaviour. Gaze perception and its cognitive underpinnings are much studied in primates, but the specific features that are used to estimate gaze can be difficult to isolate behaviourally. We photographed 13 laboratory-housed tufted capuchin monkeys (Sapajus [Cebus] apella) to quantify chromatic and achromatic contrasts between their iris, pupil, sclera and skin. We used colour vision models to quantify the degree to which capuchin eye gaze is discriminable to capuchins, their predators and their prey. We found that capuchins, regardless of their colour vision phenotype, as well as their predators, were capable of effectively discriminating capuchin gaze across ecologically relevant distances. Their prey, in contrast, were not capable of discriminating capuchin gaze, even under relatively ideal conditions. These results suggest that specific features of primate eyes can influence gaze perception, both within and across species.
Abstract.
Author URL.
2021
Šulc M, Hughes AE, Troscianko J, Štětková G, Procházka P, Požgayová M, Piálek L, Piálková R, Brlík V, Honza M, et al (2021). Automatic identification of bird females using egg phenotype. Zoological Journal of the Linnean Society, 195(1), 33-44.
Massy R, Hawkes WLS, Doyle T, Troscianko J, Menz MHM, Roberts NW, Chapman JW, Wotton KR (2021). Hoverflies use a time-compensated sun compass to orientate during autumn migration.
Proceedings of the Royal Society B: Biological Sciences,
288(1959), 20211805-20211805.
Abstract:
Hoverflies use a time-compensated sun compass to orientate during autumn migration
The sun is the most reliable celestial cue for orientation available to daytime migrants. It is widely assumed that diurnal migratory insects use a ‘time-compensated sun compass’ to adjust for the changing position of the sun throughout the day, as demonstrated in some butterfly species. The mechanisms used by other groups of diurnal insect migrants remain to be elucidated. Migratory species of hoverflies (Diptera: Syrphidae) are one of the most abundant and beneficial groups of diurnal migrants, providing multiple ecosystem services and undergoing directed seasonal movements throughout much of the temperate zone. To identify the hoverfly navigational strategy, a flight simulator was used to measure orientation responses of the hoverfliesScaeva pyrastriandScaeva seleniticato celestial cues during their autumn migration. Hoverflies oriented southwards when they could see the sun and shifted this orientation westward following a 6 h advance of their circadian clocks. Our results demonstrate the use of a time-compensated sun compass as the primary navigational mechanism, consistent with field observations that hoverfly migration occurs predominately under clear and sunny conditions.
Abstract.
Troscianko J, Nokelainen O, Skelhorn J, Stevens M (2021). Variable crab camouflage patterns defeat search image formation. Communications Biology, 4, 287-287.
2020
Heathcote RJP, Troscianko J, Darden S, Naisbett-Jones LC, Laker P, Brown AM, Ramnarine IW, Walker J, Croft D (2020). A matador-like predator diversion strategy driven by conspicuous colouration in guppies. Current Biology, 30 (14), 2844-2851.
Šulc M, Hughes AE, Troscianko J, Štětková G, Procházka P, Požgayová M, Piálek L, Piálková R, Brlík V, Honza M, et al (2020). Automatic identification of bird females using egg phenotype.
Young MMI, Winters S, Young C, Weiß BM, Troscianko J, Ganswindt A, Barrett L, Henzi SP, Higham JP, Widdig A, et al (2020). Male characteristics as predictors of genital color and display variation in vervet monkeys.
Behavioral Ecology and Sociobiology,
74(2).
Abstract:
Male characteristics as predictors of genital color and display variation in vervet monkeys
Abstract: in the animal kingdom, conspicuous colors are often used for inter- and intra-sexual communication. Even though primates are the most colorful mammalian taxon, many questions, including what potential information color signals communicate to social partners, are not fully understood. Vervet monkeys (Chlorocebus pygerythrus) are ideal to examine the covariates of color signals. Males have multi-colored genitals, which they present during distinctive male-male interactions, known as the “Red-White-and-Blue” (RWB) display, but the genitals are also visible across a variety of other contexts, and it is unclear what this color display signals to recipients. We recorded genital color presentations and standardized digital photos of male genitals (N = 405 photos) over one mating season for 20 adult males in three groups at the Samara Private Game Reserve, South Africa. We combined these with data on male characteristics (dominance, age, tenure length, injuries, and fecal glucocorticoid metabolite concentrations). Using visual modeling methods, we measured single colors (red, white, blue) but also the contrasts between colors. We assessed the frequency of the RWB genital display and male variation in genital coloration and linked this to male characteristics. Our data suggest that the number of genital displays increased with male dominance. However, none of the variables investigated explained the inter- and intra-individual variation in male genital coloration. These results suggest that the frequency of the RWB genital display, but not its color value, is related to dominance, providing valuable insights on covariation in color signals and their display in primates. Significance statement: Conspicuous colors in animals often communicate individual quality to mates and rivals. By investigating vervet monkeys, a primate species in which males present their colorful genitals within several behavioral displays, we aim to identify the covariates of such colorful signals and their behavioral display. Using visual modeling methods for the color analysis and combining behavioral display data and color data with male characteristics, we found that high-ranking males displayed their colorful genitals more frequently than lower-ranking ones. In contrast, color variation was not influenced by male dominance, age, tenure length, or health. Our results can serve as a basis for future investigations on the function of colorful signals and behavioral displays, such as a badge of status or mate choice in primates.
Abstract.
Jamie GA, Van Belleghem SM, Hogan BG, Hamama S, Moya C, Troscianko J, Stoddard MC, Kilner RM, Spottiswoode CN (2020). Multimodal mimicry of hosts in a radiation of parasitic finches.
Evolution,
74(11), 2526-2538.
Abstract:
Multimodal mimicry of hosts in a radiation of parasitic finches.
Brood parasites use the parental care of others to raise their young and sometimes employ mimicry to dupe their hosts. The brood-parasitic finches of the genus Vidua are a textbook example of the role of imprinting in sympatric speciation. Sympatric speciation is thought to occur in Vidua because their mating traits and host preferences are strongly influenced by their early host environment. However, this alone may not be sufficient to isolate parasite lineages, and divergent ecological adaptations may also be required to prevent hybridization collapsing incipient species. Using pattern recognition software and classification models, we provide quantitative evidence that Vidua exhibit specialist mimicry of their grassfinch hosts, matching the patterns, colors and sounds of their respective host's nestlings. We also provide qualitative evidence of mimicry in postural components of Vidua begging. Quantitative comparisons reveal small discrepancies between parasite and host phenotypes, with parasites sometimes exaggerating their host's traits. Our results support the hypothesis that behavioral imprinting on hosts has not only enabled the origin of new Vidua species, but also set the stage for the evolution of host-specific, ecological adaptations.
Abstract.
Author URL.
van den Berg C, Troscianko J, Endler JA, Marshall NJ, Cheney KL (2020). Quantitative Colour Pattern Analysis (QCPA): a comprehensive framework for the analysis of colour patterns in nature.
METHODS IN ECOLOGY AND EVOLUTION,
11(2), 316-332.
Author URL.
Yong L, Croft DP, Troscianko J, Ramnarine I, Wilson A (2020). Sensory-based quantification of male colour patterns in Trinidadian guppies reveals nonparallel phenotypic evolution across an ecological transition in multivariate trait space.
Abstract:
Sensory-based quantification of male colour patterns in Trinidadian guppies reveals nonparallel phenotypic evolution across an ecological transition in multivariate trait space
ABSTRACTParallel evolution, in which independent populations evolve along similar phenotypic trajectories, offers insights into the repeatability of adaptive evolution. Here, we revisit a classic example of parallelism, that of repeated evolution of brighter males in the Trinidadian guppy. In guppies, colonisation of low predation habitats is associated with emergence of ‘more colourful’ phenotypes since predator-induced viability selection for crypsis weakens while sexual selection by female preference for conspicuity remains strong. Our study differs from previous investigations in three respects. First, we adopt a multivariate phenotyping approach to characterise parallelism in multi-trait space. Second, we use ecologically-relevant colour traits defined by the visual systems of the two selective agents (i.e. guppy, predatory cichlid). Third, we estimate population genetic structure to test for adaptive (parallel) evolution against a model of neutral phenotypyc divergence. We find strong phenotypic differentiation that is inconsistent with a neutral model, but only limited support for the predicted pattern of greater conspicuity at low predation. Effects of predation regime on each trait were in the expected direction, but weak, largely non-significant, and explained little among-population variation. In multi-trait space, phenotypic trajectories of lineages colonising low from high predation regimes were not parallel. Our results are consistent with reduced predation risk facilitating adaptive differentiation by female choice, but suggest that this proceeds in (effectively) independent directions of multi-trait space across lineages. Pool-sequencing data also revealed SNPs showing greater differentiation than expected under neutrality and/or associations with known colour genes in other species, presenting opportunities for future genetic study.
Abstract.
Stephenson JF, Stevens M, Troscianko J, Jokela J (2020). The Size, Symmetry, and Color Saturation of a Male Guppy's Ornaments Forecast His Resistance to Parasites.
AMERICAN NATURALIST,
196(5), 597-608.
Author URL.
2019
Šulc M, Troscianko J, Štětková G, Hughes AE, Jelínek V, Capek M, Honza M (2019). Mimicry cannot explain rejection type in a host–brood parasite system.
Animal Behaviour,
155, 111-118.
Abstract:
Mimicry cannot explain rejection type in a host–brood parasite system
One of the most effective defensive strategies of hosts against brood parasites is rejection, commonly achieved by ejection of the parasitic egg or desertion of the parasitized nest. Nest desertion should be a costlier strategy than egg ejection, because birds must thesn spend additional time and energy renesting, and therefore we still cannot explain why some individuals desert their nests rather than eject parasitic eggs and continue a given breeding attempt. The great reed warbler, Acrocephalus arundinaceus, is a frequent host of the common cuckoo, Cuculus canorus, and is known to use both types of rejection response. By measuring cuckoo egg mimicry, we investigated the hypothesis that the hosts desert if they cannot reliably recognize the cuckoo egg in their nest. We predicted that we would find better mimicry when hosts deserted rather than ejected. However, we did not find a difference in mimicry between these two groups of nests, implying that host females do not desert because they cannot reliably recognize the parasitic egg. We also showed that neither the date in the season nor the age of the host females influenced the type of rejection. Other factors potentially eliciting nest desertion, including host personality, host, inability to eject, excessive clutch reduction and visibility of the cuckoo female at the host nest, are discussed. Finally, we suggest that desertion may persist as a host defensive strategy against brood parasitism because it is not as costly as previously assumed and/or it is beneficial for host females in good physical condition.
Abstract.
Hughes AE, Griffiths D, Troscianko J, Kelley LA (2019). No evidence for motion dazzle in an evolutionary citizen science game.
Abstract:
No evidence for motion dazzle in an evolutionary citizen science game
AbstractThe motion dazzle hypothesis posits that high contrast geometric patterns can cause difficulties in tracking a moving target, and has been argued to explain the patterning of animals such as zebras. Research to date has only tested a small number of patterns, offering equivocal support for the hypothesis. Here, we take a genetic programming approach to allow patterns to evolve based on their fitness (time taken to capture) and thus find the optimal strategy for providing protection when moving. Our ‘Dazzle Bug’ citizen science game tested over 1.5 million targets in a touch screen game at a popular visitor attraction. Surprisingly, we found that targets lost pattern elements during evolution and became closely background matching. Modelling results suggested that targets with lower motion energy were harder to catch. Our results indicate that low contrast, featureless targets offer the greatest protection against capture when in motion, challenging the motion dazzle hypothesis.
Abstract.
van den Berg CP, Troscianko J, Endler JA, Marshall NJ, Cheney KL (2019). Quantitative Colour Pattern Analysis (QCPA): a Comprehensive Framework for the Analysis of Colour Patterns in Nature.
Koleček J, Šulc M, Piálková R, Troscianko J, Požgayová M, Honza M, Procházka P (2019). Rufous Common Cuckoo chicks are not always female.
Journal of Ornithology,
160(1), 155-163.
Abstract:
Rufous Common Cuckoo chicks are not always female
The Common Cuckoo (hereafter Cuckoo) shows two adult plumage morphs—adult male plumage is grey and adult females are either grey or, less frequently, rufous. The situation is less clear in juveniles, as both sexes exhibit variable proportions of grey and rufous colour. We thus describe the patterns related to sex-specific plumage colour variation in a central European Cuckoo population. We genetically determined the sex of 91 Cuckoo chicks and using visual classification of photographs we scored juvenile plumage colouration of individual chicks into five classes based upon the increasing proportion of rufous colour on feathers. To verify these scores, we sampled chick feathers and quantified the proportion of rufous colour of individual feathers by digital image analysis. We found that juvenile females had a higher proportion of rufous colour of feathers than juvenile males. However, the difference was marginally non-significant based on visual inspection alone, and some male chicks even showed intensively rufous plumage like those of juvenile females. In contrast, we captured only grey adult males (n = 37), while five out of 20 adult females were rufous. The rufous colour of Cuckoo feathers considerably differed from the grey colour and the difference seemed to be larger in adults than in juveniles. We show that chicks, unlike adult females, cannot be visually assigned to either of the adult morphs. Therefore, we encourage further investigation of Cuckoo plumage colouration across the species’ range to examine the process of plumage maturation. A detailed genetic analysis is necessary to understand the origin of Cuckoo feather colouration.
Abstract.
Hawkes MF, Duffy E, Joag R, Skeats A, Radwan J, Wedell N, Sharma MD, Hosken DJ, Troscianko J (2019). Sexual selection drives the evolution of male wing interference patterns.
Proc Biol Sci,
286(1903).
Abstract:
Sexual selection drives the evolution of male wing interference patterns.
The seemingly transparent wings of many insects have recently been found to display unexpected structural coloration. These structural colours (wing interference patterns: WIPs) may be involved in species recognition and mate choice, yet little is known about the evolutionary processes that shape them. Furthermore, to date investigations of WIPs have not fully considered how they are actually perceived by the viewers' colour vision. Here, we use multispectral digital imaging and a model of Drosophila vision to compare WIPs of male and female Drosophila simulans from replicate populations forced to evolve with or without sexual selection for 68 generations. We show that WIPs modelled in Drosophila vision evolve in response to sexual selection and provide evidence that WIPs correlate with male sexual attractiveness. These findings add a new element to the otherwise well-described Drosophila courtship display and confirm that wing colours evolve through sexual selection.
Abstract.
Author URL.
Dell’Aglio DD, Troscianko J, Stevens M, McMillan WO, Jiggins CD (2019). The conspicuousness of the toxic<i>Heliconius</i>butterflies across time and habitat.
Abstract:
The conspicuousness of the toxicHeliconiusbutterflies across time and habitat
AbstractForests are a mosaic of light spectra, and colour signal efficiency might change in different light environments. Local adaptation inHeliconiusbutterflies is linked to microhabitat use and the colourful wing colour patterns may be adapted for signalling in different light environments. These toxic butterflies exhibit conspicuous colours as a warning to predators that they should be avoided, but also find and choose potential mates based on colour signals. The two selection pressures of predation and mate preference are therefore acting together. Colour conspicuousness should show habitat-specific contrast for the butterflies, which would facilitate detection and species identification. On the other hand, selection for signal stability would be stronger in the avian visual system. In this study we analysed the contrast of twoHeliconiusmimicry rings in their natural habitats under varying degrees of forest fragmentation and light conditions. We used digital image analyses and mapped the bird and butterfly vision colour space in order to examine whether warning colours have greater contrast and if they transmit a consistent signal across time of the day and habitat in a tropical forest. We tested conspicuousness using opponent colour channels against a natural green background. For avian vision, colours are generally very stable through time and habitat. For butterfly vision, there is some evidence that species are more contrasting in their own habitats, where conspicuousness is higher for red and yellow bands in the border and for white in the forest. Light environment affectsHeliconiusbutterflies’ warning signal transmission to a higher degree through their own vision, but to a lesser degree through avian predator vision. This work provides insight into the use of colour signals in sexual and natural selection in the light of ecological adaptation.
Abstract.
2018
Troscianko J, Skelhorn J, Stevens M (2018). Camouflage strategies interfere differently with observer search images. Proceedings of the Royal Society B: Biological Sciences, 285, 20181386-20181386.
Troscianko J, Skelhorn J, Stevens M (2018). Camouflage strategies interfere differently with observer search images.
Proceedings of the Royal Society B: Biological Sciences,
285(1886).
Abstract:
Camouflage strategies interfere differently with observer search images
Numerous animals rely on camouflage for defence. Substantial past work has identified the presence of multiple strategies for concealment, and tested the mechanisms underpinning how they work. These include background matching, D-RUP coloration to destroy target edges, and distractive markings that may divert attention from key target features. Despite considerable progress, work has focused on how camouflage types prevent initial detection by naive observers. However, predators will often encounter multiple targets over time, providing the opportunity to learn or focus attention through search images. At present, we know almost nothing about how camouflage types facilitate or hinder predator performance over repeated encounters. Here, we use experiments with human subjects searching for targets on touch screens with different camouflage strategies, and control the experience that subjects have with target types. We show that different camouflage strategies affect how subjects improve in detecting targets with repeated encounters, and how performance in detection of one camouflage type depends on experience of other strategies. In particular, disruptive coloration is effective at preventing improvements in camouflage breaking during search image formation, and experience with one camouflage type (distraction) can decrease the ability of subjects to switch to and from search images for new camouflage types (disruption). Our study is, to our knowledge, the first to show how the success of camouflage strategies depends on how they prevent initial and successive detection, and on predator experience of other strategies. This has implications for the evolution of prey phenotypes, how we assess the efficacy of defences, and predator-prey dynamics.
Abstract.
Ligon RA, Diaz CD, Morano JL, Troscianko J, Stevens M, Moskeland A, Laman TG, Scholes E (2018). Evolution of correlated complexity in the radically different courtship signals of birds-of-paradise. PLoS Biology, 16, e2006962-e2006962.
Ligon RA, Diaz CD, Morano JL, Troscianko J, Stevens M, Moskeland A, Laman TG, Scholes E (2018). Evolution of correlated complexity in the radically different courtship signals of birds-of-paradise.
Gómez J, Ramo C, Troscianko J, Stevens M, Castro M, Pérez-Hurtado A, Liñán-Cembrano G, Amat JA (2018). Individual egg camouflage is influenced by microhabitat selection and use of nest materials in ground-nesting birds. Behavioral Ecology and Sociobiology, 72, 142-142.
Gómez J, Ramo C, Stevens M, Liñán-Cembrano G, Rendón MA, Troscianko J, Amat JA (2018). Latitudinal variation in biophysical characteristics of avian eggshells to cope with differential effects of solar radiation. Ecology and Evolution, 8, 8019-8029.
Hawkes M, Duffy E, Joag R, Skeats A, Radwan J, Wedell N, Sharma, Hosken D, Troscianko J (2018). Sexual selection drives the evolution of wing interference patterns.
Holmes GG, Delferrière E, Rowe C, Troscianko J, Skelhorn J (2018). Testing the feasibility of the startle-first route to deimatism.
Sci Rep,
8(1).
Abstract:
Testing the feasibility of the startle-first route to deimatism.
Many prey species perform deimatic displays that are thought to scare or startle would-be predators, or elicit other reflexive responses that lead to attacks being delayed or abandoned. The form of these displays differs among species, but often includes prey revealing previously-hidden conspicuous visual components. The evolutionary route(s) to deimatism are poorly understood, but it has recently been suggested that the behavioural component of the displays evolves first followed by a conspicuous visual component. This is known as the "startle-first hypothesis". Here we use an experimental system in which naïve domestic chicks forage for artificial deimatic prey to test the two key predictions of this hypothesis: (1) that movement can deter predators in the absence of conspicuously coloured display components; and, (2) that the combination of movement and conspicuously coloured display components is more effective than movement alone. We show that both these predictions hold, but only when the movement is fast. We thus provide evidence for the feasibility of 'the startle-first hypothesis' of the evolution of deimatism.
Abstract.
Author URL.
2017
Abernathy VE, Troscianko J, Langmore NE (2017). Egg mimicry by the Pacific koel: mimicry of one host facilitates exploitation of other hosts with similar egg types.
Journal of Avian Biology,
48(11), 1414-1424.
Abstract:
Egg mimicry by the Pacific koel: mimicry of one host facilitates exploitation of other hosts with similar egg types
When brood parasites exploit multiple host species, egg rejection by hosts may select for the evolution of host-specific races, where each race mimics a particular host's egg type. However, some brood parasites that exploit multiple hosts with the ability to reject foreign eggs appear to have only a single egg type. In these cases, it is unclear how the parasite egg escapes detection by its hosts. Three possible explanations are: 1) host-specific races are present, but differences in egg morphology are difficult for the human eye to detect; 2) the brood parasite evolves a single egg type that is intermediate in appearance between the eggs of its hosts; 3) or the parasite evolves mimicry of one of its hosts, which subsequently allows it to exploit other species with similar egg morphology. Here we test these possibilities by quantifying parameters of egg appearance of the brood-parasitic Pacific koel Eudynamys orientalis and seven of its hosts. Koel eggs laid in the nests of different hosts did not show significant differences in colour or pattern, suggesting that koels have not evolved host-specific races. Koel eggs were similar in colour, luminance and pattern to the majority of hosts, but were significantly more similar in colour and luminance to one of the major hosts than to two other major hosts, supporting hypothesis 3. Our findings suggest that mimicry of one host can allow a brood parasite to exploit new hosts with similar egg morphologies, which could inhibit the evolution of host defences in naïve hosts.
Abstract.
Stevens M, Troscianko J, Wilson-Aggarwal JK, Spottiswoode CN (2017). Improvement of individual camouflage through background choice in ground-nesting birds. Nature Ecology and Evolution, 1, 1325-1325.
Koski T-M, Lindstedt C, Klemola T, Troscianko J, Mäntylä E, Tyystjärvi E, Stevens M, Helander M, Laaksonen T (2017). Insect herbivory may cause changes in the visual properties of leaves and affect the camouflage of herbivores to avian predators. Behavioral Ecology and Sociobiology, 31, 97-97.
Troscianko J, Skelhorn J, Stevens M (2017). Quantifying camouflage: how to predict detectability from appearance. BMC Evolutionary Biology, 17, 7-7.
Troscianko J, Wilson-Aggarwal J, Griffiths D, Spottiswoode CN, Stevens M (2017). Relative advantages of dichromatic and trichromatic color vision in camouflage breaking. Behavioral Ecology, 28, 556-556.
Robledo-Ospina LE, Escobar-Sarria F, Troscianko J, Rao D (2017). Two ways to hide: predator and prey perspectives of disruptive coloration and background matching in jumping spiders.
BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY,
122(4), 752-764.
Author URL.
2016
Medina I, Troscianko J, Stevens M, Langmore NE (2016). Brood Parasitism is Linked to Egg Pattern Diversity within and among Species of Australian Passerines.
Am Nat,
187(3), 351-362.
Abstract:
Brood Parasitism is Linked to Egg Pattern Diversity within and among Species of Australian Passerines.
Bird eggs show striking diversity in color and pattern. One explanation for this is that interactions between avian brood parasites and their hosts drive egg phenotype evolution. Brood parasites lay their eggs in the nests of other species, their hosts. Many hosts defend their nests against parasitism by rejecting foreign eggs, which selects for parasite eggs that mimic those of the host. In theory, this may in turn select for changes in host egg phenotypes over time to facilitate discrimination of parasite eggs. Here, we test for the first time whether parasitism by brood parasites has led to increased divergence in egg phenotype among host species. Using Australian host and nonhost species and objective measures of egg color and pattern, we show that (i) hosts of brood parasites have higher within-species variation in egg pattern than nonhosts, supporting previous findings in other systems, and (ii) host species have diverged more in their egg patterns than nonhost species after controlling for divergence time. Overall, our results suggest that brood parasitism has played a significant role in the evolution of egg diversity and that these effects are evident, not only within species, but also among species.
Abstract.
Author URL.
Troscianko J, Wilson-Aggarwal J, Stevens M, Spottiswoode CN (2016). Camou age predicts survival in ground-nesting birds. Scientific Reports, 6
Wilson-Aggarwal, Troscianko, Stevens M, Spottiswoode CN (2016). Escape distance in ground-nesting birds differs with individual level of camouflage. The American Naturalist, 188, 231-231.
De Gasperin O, Duarte A, Troscianko J, Kilner RM (2016). Fitness costs associated with building and maintaining the burying beetle's carrion nest.
Sci Rep,
6Abstract:
Fitness costs associated with building and maintaining the burying beetle's carrion nest.
It is well-known that features of animal nest architecture can be explained by fitness benefits gained by the offspring housed within. Here we focus on the little-tested suggestion that the fitness costs associated with building and maintaining a nest should additionally account for aspects of its architecture. Burying beetles prepare an edible nest for their young from a small vertebrate carcass, by ripping off any fur or feathers and rolling the flesh into a rounded ball. We found evidence that only larger beetles are able to construct rounder carcass nests, and that rounder carcass nests are associated with lower maintenance costs. Offspring success, however, was not explained by nest roundness. Our experiment thus provides rare support for the suggestion that construction and maintenance costs are key to understanding animal architecture.
Abstract.
Author URL.
Troscianko, Wilson-Aggarwal, Spottiswoode CN, Stevens M (2016). Nest covering in plovers: how modifying the visual environment influences egg camouflage. Ecology and Evolution, 6, 7536-7545.
2015
Troscianko J, Rutz C (2015). Activity profiles and hook-tool use of New Caledonian crows recorded by bird-borne video cameras.
Biol Lett,
11(12).
Abstract:
Activity profiles and hook-tool use of New Caledonian crows recorded by bird-borne video cameras.
New Caledonian crows are renowned for their unusually sophisticated tool behaviour. Despite decades of fieldwork, however, very little is known about how they make and use their foraging tools in the wild, which is largely owing to the difficulties in observing these shy forest birds. To obtain first estimates of activity budgets, as well as close-up observations of tool-assisted foraging, we equipped 19 wild crows with self-developed miniature video cameras, yielding more than 10 h of analysable video footage for 10 subjects. While only four crows used tools during recording sessions, they did so extensively: across all 10 birds, we conservatively estimate that tool-related behaviour occurred in 3% of total observation time, and accounted for 19% of all foraging behaviour. Our video-loggers provided first footage of crows manufacturing, and using, one of their most complex tool types--hooked stick tools--under completely natural foraging conditions. We recorded manufacture from live branches of paperbark (Melaleuca sp.) and another tree species (thought to be Acacia spirorbis), and deployment of tools in a range of contexts, including on the forest floor. Taken together, our video recordings reveal an 'expanded' foraging niche for hooked stick tools, and highlight more generally how crows routinely switch between tool- and bill-assisted foraging.
Abstract.
Author URL.
Burriss R, Troscianko J, Lovell PG, Fulford AJC, Stevens M, Quigley R, Payne J, Saxton TK, Rowland HM (2015). Changes in Women’s Facial Skin Color over the Ovulatory Cycle are Not Detectable by the Human Visual System. PLoS ONE, 10, e0130093-e0130093.
Troscianko J, Stevens M, Skelhorn J (2015). Does Disruptive Camouflage Disrupt Search Image Formation?.
PERCEPTION,
44(10), 1239-1240.
Author URL.
Feeney WE, Troscianko J, Langmore NE, Spottiswoode CN (2015). Evidence for aggressive mimicry in an adult brood parasitic bird, and generalized defences in its host.
Proc Biol Sci,
282(1810).
Abstract:
Evidence for aggressive mimicry in an adult brood parasitic bird, and generalized defences in its host.
Mimicry of a harmless model (aggressive mimicry) is used by egg, chick and fledgling brood parasites that resemble the host's own eggs, chicks and fledglings. However, aggressive mimicry may also evolve in adult brood parasites, to avoid attack from hosts and/or manipulate their perception of parasitism risk. We tested the hypothesis that female cuckoo finches (Anomalospiza imberbis) are aggressive mimics of female Euplectes weavers, such as the harmless, abundant and sympatric southern red bishop (Euplectes orix). We show that female cuckoo finch plumage colour and pattern more closely resembled those of Euplectes weavers (putative models) than Vidua finches (closest relatives); that their tawny-flanked prinia (Prinia subflava) hosts were equally aggressive towards female cuckoo finches and southern red bishops, and more aggressive to both than to their male counterparts; and that prinias were equally likely to reject an egg after seeing a female cuckoo finch or bishop, and more likely to do so than after seeing a male bishop near their nest. This is, to our knowledge, the first quantitative evidence for aggressive mimicry in an adult bird, and suggests that host-parasite coevolution can select for aggressive mimicry by avian brood parasites, and counter-defences by hosts, at all stages of the reproductive cycle.
Abstract.
Author URL.
Troscianko J, Stevens M (2015). Image Calibration and Analysis Toolbox – a free software suite for objectively measuring reflectance, colour and pattern. Methods in Ecology and Evolution, 6, 1320-1331.
2014
Troscianko J (2014). A simple tool for calculating egg shape, volume and surface area from digital images.
Ibis,
156(4), 874-878.
Abstract:
A simple tool for calculating egg shape, volume and surface area from digital images
The geometrical properties of eggs - such as volume and surface area - have uses ranging from ecological, physiological and morphological studies in birds, to predictions of chick condition in the poultry industry. Although measurements of an egg's length and breadth can be used to approximate its geometry, the coefficients used in these models are specific to the original test population, and intraspecific variation in egg shape means these methods cannot be used reliably beyond that population. Here I present a novel mathematical formula to describe the curvature of a bird's egg that can be used to calculate the shape, volume and surface area of an egg precisely from digital images. Using data from several species I demonstrate that the model has a greater level of accuracy than length- and breadth-based methods, and release the user-friendly tool for others to use for measuring eggs from digital images.
Abstract.
Arenas LM, Troscianko J, Stevens M (2014). Color contrast and stability as key elements for effective warning signals. Frontiers in Ecology and Evolution, 2
Hughes AE, Troscianko J, Stevens M (2014). Motion dazzle and the effects of target patterning on capture success.
BMC Evol Biol,
14Abstract:
Motion dazzle and the effects of target patterning on capture success.
BACKGROUND: Stripes and other high contrast patterns found on animals have been hypothesised to cause "motion dazzle", a type of defensive coloration that operates when in motion, causing predators to misjudge the speed and direction of object movement. Several recent studies have found some support for this idea, but little is currently understood about the mechanisms underlying this effect. Using humans as model 'predators' in a touch screen experiment we investigated further the effectiveness of striped targets in preventing capture, and considered how stripes compare to other types of patterning in order to understand what aspects of target patterning are important in making a target difficult to capture. RESULTS: We find that striped targets are among the most difficult to capture, but that other patterning types are also highly effective at preventing capture in this task. Several target types, including background sampled targets and targets with a 'spot' on were significantly easier to capture than striped targets. We also show differences in capture attempt rates between different target types, but we find no differences in learning rates between target types. CONCLUSIONS: We conclude that striped targets are effective in preventing capture, but are not uniquely difficult to catch, with luminance matched grey targets also showing a similar capture rate. We show that key factors in making capture easier are a lack of average background luminance matching and having trackable 'features' on the target body. We also find that striped patterns are attempted relatively quickly, despite being difficult to catch. We discuss these findings in relation to the motion dazzle hypothesis and how capture rates may be affected more generally by pattern type.
Abstract.
Author URL.
2013
Troscianko J, Lown AE, Hughes AE, Stevens M (2013). Defeating crypsis: detection and learning of camouflage strategies.
PLoS One,
8(9).
Abstract:
Defeating crypsis: detection and learning of camouflage strategies.
Camouflage is perhaps the most widespread defence against predators in nature and an active area of interdisciplinary research. Recent work has aimed to understand what camouflage types exist (e.g. background matching, disruptive, and distractive patterns) and their effectiveness. However, work has almost exclusively focused on the efficacy of these strategies in preventing initial detection, despite the fact that predators often encounter the same prey phenotype repeatedly, affording them opportunities to learn to find those prey more effectively. The overall value of a camouflage strategy may, therefore, reflect both its ability to prevent detection by predators and resist predator learning. We conducted four experiments with humans searching for hidden targets of different camouflage types (disruptive, distractive, and background matching of various contrast levels) over a series of touch screen trials. As with previous work, disruptive coloration was the most successful method of concealment overall, especially with relatively high contrast patterns, whereas potentially distractive markings were either neutral or costly. However, high contrast patterns incurred faster decreases in detection times over trials compared to other stimuli. In addition, potentially distractive markings were sometimes learnt more slowly than background matching markings, despite being found more readily overall. Finally, learning effects were highly dependent upon the experimental paradigm, including the number of prey types seen and whether subjects encountered targets simultaneously or sequentially. Our results show that the survival advantage of camouflage strategies reflects both their ability to avoid initial detection (sensory mechanisms) and predator learning (perceptual mechanisms).
Abstract.
Author URL.
Rutz C, Troscianko J (2013). Programmable, miniature video-loggers for deployment on wild birds and other wildlife.
Methods in Ecology and Evolution,
4(2), 114-122.
Abstract:
Programmable, miniature video-loggers for deployment on wild birds and other wildlife
Animal-borne miniature video cameras hold the potential to revolutionise field ornithological research, with their ability to collect detailed behavioural data from a bird's eye view, in places and contexts where conventional observation techniques would fail. Here, we describe the development of a new generation of solid-state video-loggers that are cheap, light-weight, programmable and easy to use and that overcome many problems associated with earlier transmission-based technologies. Our loggers weigh c. 12·3-13·6 g fully packaged for deployment and record up to 94 min of video footage, at 640 × 480 pixels and 19·7 frames per second, on a 4-GB micro-SD card. Loggers are fitted with a custom-designed, microprocessor-controlled timer that enables flexible duty-cycling, switching the unit on and off following a preprogrammed schedule. Packaged loggers contain a miniature very high frequency (VHF) radio-tag (battery life c. 5-9 weeks) for positional tracking of the bird before, during and after scheduled video shoots, and to enable logger recovery for data download. To make our loggers suitable for deployment on wild birds, we developed novel techniques: (i) for the light-weight packaging of electronics (thin sheets produced from thermoplastic) and (ii) for the attachment of units to, and their controlled release from, subjects (UV-sensitive, rapidly degrading rubber tubing). Loggers can be manufactured at comparatively low cost (components are c. 94 GBP, plus c. 145 GBP for the VHF radio-tag) and are easily refurbished after recovery, making the technology suitable for large-scale deployments and projects on modest research budgets. A study in 2009/2010, with logger deployments on 19 wild New Caledonian crows Corvus moneduloides, demonstrated that our new technology is field-worthy and that it can generate rich data sets on the foraging behaviour, habitat use and social interactions of an elusive bird species. The young field of wildlife video-tracking is maturing quickly, and in only a few years, technology has advanced sufficiently to enable cost-effective, hypothesis-driven field studies of terrestrial birds, mammals and reptiles. Large-scale deployment of video-loggers can generate data sets of unprecedented information content, promising major quantitative insights in basic and applied ecology. © 2012 the Authors. Methods in Ecology and Evolution © 2012 British Ecological Society.
Abstract.
Stevens M, Troscianko J, Spottiswoode CN (2013). Repeated targeting of the same hosts by a brood parasite compromises host egg rejection.
Nat Commun,
4Abstract:
Repeated targeting of the same hosts by a brood parasite compromises host egg rejection.
Cuckoo eggs famously mimic those of their foster parents to evade rejection from discriminating hosts. Here we test whether parasites benefit by repeatedly parasitizing the same host nest. This should make accurate rejection decisions harder, regardless of the mechanism that hosts use to identify foreign eggs. Here we find strong support for this prediction in the African tawny-flanked prinia (Prinia subflava), the most common host of the cuckoo finch (Anomalospiza imberbis). We show experimentally that hosts reject eggs that differ from an internal template, but crucially, as the proportion of foreign eggs increases, hosts are less likely to reject them and require greater differences in appearance to do so. Repeated parasitism by the same cuckoo finch female is common in host nests and likely to be an adaptation to increase the probability of host acceptance. Thus, repeated parasitism interacts with egg mimicry to exploit cognitive and sensory limitations in host defences.
Abstract.
Author URL.
Stevens M, Marshall KLA, Troscianko J, Finlay S, Burnand D, Chadwick SL (2013). Revealed by conspicuousness: Distractive markings reduce camouflage.
Behavioral Ecology,
24(1), 213-222.
Abstract:
Revealed by conspicuousness: Distractive markings reduce camouflage
Animal camouflage is a textbook example of natural selection. Despite substantial progress, one historical theory remains controversial: that conspicuous "distractive" markings draw predator attention away from the prey outline, preventing detection. Here, we present evidence from 4 experiments to resolve this controversy. In field experiments, we measured bird predation on artificial cryptic prey that were either unmarked or had distractive markings of various attributes (number, color, and location). Prey with 3 high-contrast distractive markings, and with markings located away from the body outline, suffered reduced survival compared with unmarked controls or prey with low-contrast markings. There was no effect of small single markings with different colors on the survival of targets. In 2 computer-based experiments with human subjects searching for hidden targets, distractive markings of various types (number, size, and location) reduced detection times compared with controls. This effect was greatest for targets that had large or 3 markings. In addition, small and centrally placed markings facilitated faster learning. Therefore, these 2 experimental approaches show that distractive markings are detrimental to camouflage, both facilitating initial detection and increasing the speed of predator learning. Our experiments also suggest that learning of camouflaged prey is dependent on the type of camouflage present. Contrary to current and historical discussion, conspicuous markings are more likely to impair camouflage than enhance it, presenting important implications for the optimization of prey coloration in general. © 2012 the Author.
Abstract.
Stevens M, Troscianko J, Marshall KLA, Finlay S (2013). What is camouflage through distractive markings a reply to Merilaita et al. (2013). Behavioral Ecology, 24(5).
2012
Troscianko J, von Bayern AMP, Chappell J, Rutz C, Martin GR (2012). Extreme binocular vision and a straight bill facilitate tool use in New Caledonian crows.
Nat Commun,
3Abstract:
Extreme binocular vision and a straight bill facilitate tool use in New Caledonian crows.
Humans are expert tool users, who manipulate objects with dextrous hands and precise visual control. Surprisingly, morphological predispositions, or adaptations, for tool use have rarely been examined in non-human animals. New Caledonian crows Corvus moneduloides use their bills to craft complex tools from sticks, leaves and other materials, before inserting them into deadwood or vegetation to extract prey. Here we show that tool use in these birds is facilitated by an unusual visual-field topography and bill shape. Their visual field has substantially greater binocular overlap than that of any other bird species investigated to date, including six non-tool-using corvids. Furthermore, their unusually straight bill enables a stable grip on tools, and raises the tool tip into their visual field's binocular sector. These features enable a degree of tool control that would be impossible in other corvids, despite their comparable cognitive abilities. To our knowledge, this is the first evidence for tool-use-related morphological features outside the hominin lineage.
Abstract.
Author URL.
Hughes A, Troscianko J, Tolhurst D, Stevens M (2012). Prey movement and the mechanisms of dazzle coloration.
PERCEPTION,
41(10), 1271-1271.
Author URL.
2010
Rutz CR, Bluff LA, Reed N, Troscianko J, Newton J, Inger R, Kacelnik A, Bearhop S (2010). The Ecological Significance of Tool Use in New Caledonian Crows.
Science,
329, 1523-1525.
Abstract:
The Ecological Significance of Tool Use in New Caledonian Crows
Tool use is so rare in the animal kingdom that its evolutionary origins cannot be traced with comparative analyses. Valuable insights can be gained from investigating the ecological context and adaptive significance of tool use under contemporary conditions, but obtaining robust observational data is challenging. We assayed individual-level tool-use dependence in wild
New Caledonian crows by analyzing stable isotope profiles of the birds’ feathers, blood, and putative food sources. Bayesian diet-mixing models revealed that a substantial amount of the crows’ protein and lipid intake comes from prey obtained with stick tools—wood-boring beetle larvae. Our calculations provide estimates of larva-intake rates and show that just a few larvae can satisfy a crow’s daily energy requirements, highlighting the substantial rewards available to competent tool users.
Abstract.
Bluff LA, Troscianko J, Weir AAS, Kacelnik A, Rutz C (2010). Tool use by wild New Caledonian crows Corvus moneduloides at natural foraging sites.
Proc Biol Sci,
277(1686), 1377-1385.
Abstract:
Tool use by wild New Caledonian crows Corvus moneduloides at natural foraging sites.
New Caledonian crows Corvus moneduloides use tools made from sticks or leaf stems to 'fish' woodboring beetle larvae from their burrows in decaying wood. Previous research on this behaviour has been confined to baited sites, leaving its ecological context and significance virtually unexplored. To obtain detailed observations of natural, undisturbed tool use, we deployed motion-triggered video cameras at seven larva-fishing sites. From 1797 camera hours of surveillance over 111 days, we recorded 317 site visits by at least 14 individual crows. Tool use was observed during 150 site visits. Our video footage revealed notable variation in foraging success among identifiable crows. Two nutritionally independent, immature crows spent considerable time using tools, but were much less successful than local adults, highlighting the potential role of individual and social learning in the acquisition of tool-use proficiency. During systematic surveys of larva-fishing sites, we collected 193 tools that crows had left inserted in larva burrows. Comparing these tools with the holes in which they were found, and with raw materials available around logs, provides evidence for tool selectivity by New Caledonian crows under natural conditions. Taken together, these two complementary lines of investigation provide, to our knowledge, the first quantitative description of larva fishing by wild crows in its full ecological context.
Abstract.
Author URL.
2009
Takahashi T, McDougall C, Troscianko J, Chen W-C, Jayaraman-Nagarajan A, Shimeld SM, Ferrier DEK (2009). An EST screen from the annelid Pomatoceros lamarckii reveals patterns of gene loss and gain in animals.
BMC Evol Biol,
9Abstract:
An EST screen from the annelid Pomatoceros lamarckii reveals patterns of gene loss and gain in animals.
BACKGROUND: Since the drastic reorganisation of the phylogeny of the animal kingdom into three major clades of bilaterians; Ecdysozoa, Lophotrochozoa and Deuterostomia, it became glaringly obvious that the selection of model systems with extensive molecular resources was heavily biased towards only two of these three clades, namely the Ecdysozoa and Deuterostomia. Increasing efforts have been put towards redressing this imbalance in recent years, and one of the principal phyla in the vanguard of this endeavour is the Annelida. RESULTS: in the context of this effort we here report our characterisation of an Expressed Sequence Tag (EST) screen in the serpulid annelid, Pomatoceros lamarckii. We have sequenced over 5,000 ESTs which consolidate into over 2,000 sequences (clusters and singletons). These sequences are used to build phylogenetic trees to estimate relative branch lengths amongst different taxa and, by comparison to genomic data from other animals, patterns of gene retention and loss are deduced. CONCLUSION: the molecular phylogenetic trees including the P. lamarckii sequences extend early observations that polychaetes tend to have relatively short branches in such trees, and hence are useful taxa with which to reconstruct gene family evolution. Also, with the availability of lophotrochozoan data such as that of P. lamarckii, it is now possible to make much more accurate reconstructions of the gene complement of the ancestor of the bilaterians than was previously possible from comparisons of ecdysozoan and deuterostome genomes to non-bilaterian outgroups. It is clear that the traditional molecular model systems for protostomes (e.g. Drosophila melanogaster and Caenorhabditis elegans), which are restricted to the Ecdysozoa, have undergone extensive gene loss during evolution. These ecdysozoan systems, in terms of gene content, are thus more derived from the bilaterian ancestral condition than lophotrochozoan systems like the polychaetes, and thus cannot be used as good, general representatives of protostome genomes. Currently sequenced insect and nematode genomes are less suitable models for deducing bilaterian ancestral states than lophotrochozoan genomes, despite the array of powerful genetic and mechanistic manipulation techniques in these ecdysozoans. A distinct category of genes that includes those present in non-bilaterians and lophotrochozoans, but which are absent from ecdysozoans and deuterostomes, highlights the need for further lophotrochozoan data to gain a more complete understanding of the gene complement of the bilaterian ancestor.
Abstract.
Author URL.
2008
Troscianko J, Bluff LA, Rutz C (2008). Grass-stem tool use in New Caledonian Crows Corvus moneduloides.
Ardea,
96(2), 283-285.
Abstract:
Grass-stem tool use in New Caledonian Crows Corvus moneduloides
We report an observation of a wild New Caledonian Crow Corvus moneduloides manufacturing two tools from dry grass stems, and using them to extract lizards from the crevices of a fencepost. We recovered one of the tools and were able to examine the raw material from which tools had been manufactured. This confirms our earlier observations with animal-borne video cameras, where we inferred use of this hitherto undocumented tool material from frame-by-frame analysis of video footage.
Abstract.
2005
Lovell PG, Tolhurst DJ, Párraga CA, Baddeley RJ, Leonards U, Troscianko J, Troscianko T (2005). Opponent channel responses to changes in the illuminant of natural scenes for primates and birds.
Author URL.
Lovell PG, Tolhurst DJ, Párraga CA, Baddeley R, Leonards U, Troscianko J, Troscianko T (2005). Stability of the color-opponent signals under changes of illuminant in natural scenes.
J Opt Soc Am a Opt Image Sci Vis,
22(10), 2060-2071.
Abstract:
Stability of the color-opponent signals under changes of illuminant in natural scenes.
Illumination varies greatly both across parts of a natural scene and as a function of time, whereas the spectral reflectance function of surfaces remains more stable and is of much greater relevance when searching for specific targets. This study investigates the functional properties of postreceptoral opponent-channel responses, in particular regarding their stability against spatial and temporal variation in illumination. We studied images of natural scenes obtained in UK and Uganda with digital cameras calibrated to produce estimated L-, M-, and S-cone responses of trichromatic primates (human) and birds (starling). For both primates and birds we calculated luminance and red-green opponent (RG) responses. We also calculated a primate blue-yellow-opponent (BY) response. The BY response varies with changes in illumination, both across time and across the image, rendering this factor less invariant. The RG response is much more stable than the BY response across such changes in illumination for primates, less so for birds. These differences between species are due to the greater separation of bird L and M cones in wavelength and the narrower bandwidth of the cone action spectra. This greater separation also produces a larger chromatic signal for a given change in spectral reflectance. Thus bird vision seems to suffer a greater degree of spatiotemporal "clutter" than primate vision, but also enhances differences between targets and background. Therefore, there may be a trade-off between the degree of chromatic clutter in a visual system versus the degree of chromatic difference between a target and its background. Primate and bird visual systems have found different solutions to this trade-off.
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2003
Troscianko T, Parraga CA, Leonards U, Baddeley RJ, Troscianko J, Tolhurst DJ (2003). Leaves, fruit, shadows, and lighting in kibale forest, Uganda.
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Parraga CA, Troscianko T, Troscianko J, Tolhurst DJ, Leonards U (2003). Spatiochromatic properties of images of fruits and leaves from Kibale Forest, Uganda.
Journal of Vision,
3(9).
Abstract:
Spatiochromatic properties of images of fruits and leaves from Kibale Forest, Uganda
The human visual system (hvs), as well as that of other trichromatic primates, has different contrast sensitivity functions for chromatic and luminance stimuli. The spatial filtering is low-pass for chromatic stimuli and band-pass for luminance. Previous results have shown that a subset of natural scenes, namely those with red objects (e.g.fruit) on a background of leaves have spatial properties that correspond to this physiological spatial filtering (Parraga, Troscianko and Tolhurst; Current Biology 12, 483-487; 2000). Our original dataset on which these conclusions were based was consisted of English natural scenes. Here we analysed the spatiochromatic properties of a dataset of natural scenes obtained in Kibale Forest, Uganda, which is a natural habitat containing large numbers of wild trichromatic primates. We used the same calibrated digital camera as in the previous study, which delivers L,M,S cone responses, and opponent-channel responses, for each pixel. We obtained 270 images of scenes, many of them containing red fruit, red leaves, red flowers and green leaves corresponding to the primate visual environment as seen from the ground and from the canopy. All the red fruit and leaves were confirmed as forming a significant part of the diet of trichromatic primates. Our results support the earlier finding (with English plants), namely that the luminance and chromatic Fourier spectra of pictures containing reddish objects on a background of leaves correspond well to the spatio-chromatic properties of the luminance and red-green systems in human vision, at viewing distances of the same order of magnitude as the grasping distance.
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Troscianko T, Baddeley R, Parraga CA, Leonards U, Troscianko J (2003). Visual encoding of green leaves in primate vision.
Journal of Vision,
3(9).
Abstract:
Visual encoding of green leaves in primate vision
It is known that primate red-green color vision is efficient at encoding the presence of red or yellow fruit or leaves against a background of green foliage. However, our observations of monkey foraging behavior in Kibale Forest, Uganda during the dry season suggested that monkeys frequently ate green leaves on trees lacking any red object. They also showed preferences for specific trees. We asked whether the neural encoding of the green leaves of such trees allows discrimination from other trees, across marked differences in illumination due to time-of-day and weather effects. We obtained 80 images of two scenes, each containing several types of tree, throughout two days at intervals of 10-20 minutes, using a calibrated digital camera system described elsewhere (Párraga, Troscianko, and Tolhurst Current Biology 12, 483-487; 2002). The camera calibration allowed the decomposition of each pixel into L,M,S cone responses, and also luminance, red-green, and yellow-blue opponent responses. We averaged the values of these responses in five separate patches for images from Day 1, and six patches for Day 2. Our first analysis replicated the approach of Nascimento, Ferreira, and Foster (2002) JOSA a 19, 1484-1490, who suggested that ratios of cone responses across different patches should be invariant against changes in illumination. This turned out not to hold when one of the patches was plunged into shadow. Importantly, if similar ratios are taken of the opponent-channel responses, particularly the red-green channel which shows invariance to shadows, these new ratios are more invariant across illumination changes by an order of magnitude. We conclude that the red-green opponent system provides information about scenes containing green leaves which is strongly invariant across changes in illumination direction, spectral composition, and intensity. In other words, for scenes containing foliage, the color constancy problem is solved at the level of the retina.
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