No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Food color preferences against a dark, textured background vary in relation to sex and age in house finches (Carpodacus mexicanus)
Abstract
Many animals consume colorful foods, because bright coloration either enhances conspicuousness of food items or signals nutritional rewards. A comparatively under-studied aspect of food color preferences is the role of the background environment in shaping food detectability and choices. Previous work with house finches (Carpodacus mexicanus), for example, showed that individuals preferred red and green food items and avoided yellow ones. However, this study of desert, ground-feeding birds was done with seeds presented against an artificial white background that is unlikely to reflect natural conditions. Therefore, we performed a similar experiment, but quantified selection of colorful foods using a different visual environment that better mimicked natural conditions. We mixed dark, inedible distractor pellets (i.e., analogous to natural desert sand and rocks) with sunflower kernels that were colored red, green, yellow, or orange to test for differences in foraging patterns by sex, age, and expression of male plumage coloration in non-molting house finches. This food presentation resulted in yellow seeds having a significantly greater chromatic, but not achromatic, contrast with the background than red or green seeds. Under these conditions, all birds consumed yellow, and to a lesser extent red, seeds most often, and both adult males and females had a strong preference for yellow kernels; adult males also tended to prefer green kernels, but females tended not to prefer green kernels. Juveniles showed no significant preferences for any seed color, and adult male plumage coloration was not related to seed color preference. Therefore, in contrast to studies using different foraging environments, house finches tended to prefer yellow seeds, supporting models that suggest that visual background and contrast may be more important than color per se in visually mediated foraging decisions of birds. Moreover, the fact that adult males and females differed in food color preference has not been reported previously in songbirds.
... While in most experiments bird species show consistent preferences for fruits or dyed baits of particular colours, in some colour preferences varied (Willson et al. 1990;Duan & Quan 2013;Fadzly et al. 2013;Weser & Ross 2013) or there were no significant preferences (Byrant et al. 1984). The contrast between the colour of a fruit and the background against which it is displayed may also influence bird colour preferences (Behbahaninia et al. 2012;Camargo et al. 2013;Duan & Quan 2013) and the low contrast of green fruit against a green background may in part explain why few bird-dispersed plants have green fruits (Camargo et al. 2013). Individual birds within a species may show different colour preferences depending on gender (Mastrota & Mench 1994), and colour preferences may be changed, at least in the short term, by prior exposure to coloured food (Willson et al. 1990;Larrinaga 2011;Behbahaninia et al. 2012). ...
... The contrast between the colour of a fruit and the background against which it is displayed may also influence bird colour preferences (Behbahaninia et al. 2012;Camargo et al. 2013;Duan & Quan 2013) and the low contrast of green fruit against a green background may in part explain why few bird-dispersed plants have green fruits (Camargo et al. 2013). Individual birds within a species may show different colour preferences depending on gender (Mastrota & Mench 1994), and colour preferences may be changed, at least in the short term, by prior exposure to coloured food (Willson et al. 1990;Larrinaga 2011;Behbahaninia et al. 2012). Colour preferences may also vary depending on food type (e.g. ...
Non-target risk from the use of vertebrate toxins for pest control is an ongoing issue globally. In New Zealand, toxic bait for aerial control of possums and rodents is dyed green and contains cinnamon oil, both of which are thought to reduce the risk that birds will eat the bait. It has been suggested for some time that blue dye may be a more effective feeding deterrent than green dye. While both green and blue dye reduce the risk that birds will feed on bait, the available evidence is not sufficiently strong to suggest a significant improvement in repelling birds by switching from green to blue. Cinnamon oil, at the nominal concentration in bait, may have some bird repellent effects, but these are likely to depend on its origin (bark or leaves) and the freshness of the bait (as it evaporates relatively quickly from bait after manufacture). Bait colour, including ultraviolet, is also an important cue in avoidance learning by birds and should be considered in more detail in future studies of specific bird repellent additives to bait for possum and rodent control. Further research is needed to optimise the use of visual cues in bait, both for their inherent repellency (e.g. green vs blue; optimal concentration of dye) and for their effectiveness in promoting avoidance learning. It would also be worth investigating an alternative compound to cinnamon as a mask for 1080; ideally such an alternative would have enhanced stability and bird repellent properties.
... Unfortunately, questions related to environmental carotenoid limitation are difficult to answer under natural conditions wherein a population of birds may consume a wide variety of food items, individuals may differ in which and how much of those various items they consume, and the internal processes of carotenoid assimilation (which may differ among individuals, species, season and even specific carotenoid pigments; McGraw, 2005;Tella et al., 2004) are largely unknown in any given study system. Studies testing for preferences for carotenoidrich food in birds with carotenoid-based ornamentation have found only mixed support (Bascuñán, Tourville, Toomey, & McGraw, 2009;Behbahaninia, Butler, Toomey, & McGraw, 2012;Catoni, Metzger, Schaefer, & Bairlein, 2011;Senar et al., 2010), indicating that many colourful birds do not need to preferentially forage for carotenoidrich food in order to produce colourful ornaments (but see Walker et al., 2014). Currently, environmental carotenoid limitation is not widely considered to be a major determinant of carotenoid-based colour signalling (Hadfield & Owens, 2006;Møller et al., 2000;Svensson & Wong, 2011). ...
1.Within the past several decades, resource tradeoffs have emerged as the commonly accepted explanation for how carotenoid‐based coloration links to individual performance. However, the literature on carotenoid signaling is inconsistent in how carotenoid resource tradeoffs are defined, assessed, and interpreted.
2.We provide a clear statement of the resource tradeoff hypothesis for explaining the honesty of carotenoid‐based ornaments, its key assumptions, and evidence for (or against) each assumption.
3.Focusing on class Aves, we perform a critical assessment of theoretical and empirical evidence for carotenoid resource limitation and for direct physiological benefits of carotenoid pigments to immune and antioxidant performance.
4.We identify important inconsistencies in how data related to physiological function and carotenoid coloration have been interpreted in light of the resource tradeoff hypothesis, and we suggest directions for future research. This article is protected by copyright. All rights reserved.
... In the agile mouse opossum (Gracilianus agilis), females consumed more fruits and defaecated more seeds than males (de Camargo et al., 2011), but in guenons (Cercopithecus ascanius and C. mitis) males were more frugivorous than females (Cords, 1986). In house finches (Carpodacus mexicanus), females and males preferred sunflower kernels of different colours (Behbahaninia et al., 2012). Males and females also differ behaviourally, particularly with regard to their roles during mating and breeding. ...
Seed dispersal by animals is a complex phenomenon, characterized by multiple mechanisms and variable outcomes. Most researchers approach this complexity by analysing context-dependency in seed dispersal and investigating extrinsic factors that might influence interactions between plants and seed dispersers. Intrinsic traits of seed dispersers provide an alternative way of making sense of the enormous variation in seed fates. I review causes of intraspecific variability in frugivorous and granivorous animals, discuss their effects on seed dispersal, and outline likely consequences for plant populations and communities. Sources of individual variation in seed-dispersing animals include sexual dimorphism, changes associated with growth and ageing, individual specialization, and animal personalities. Sexual dimorphism of seed-dispersing animals influences seed fate through diverse mechanisms that range from effects caused by sex-specific differences in body size, to influences of male versus female cognitive functions. These differences affect the type of seed treatment (e.g. dispersal versus predation), the number of dispersed seeds, distance of seed dispersal, and likelihood that seeds are left in favourable sites for seeds or seedlings. The best-documented consequences of individual differences associated with growth and ageing involve quantity of dispersed seeds and the quality of seed treatment in the mouth and gut. Individual specialization on different resources affects the number of dispersed plant species, and therefore the connectivity and architecture of seed-dispersal networks. Animal personalities might play an important role in shaping interactions between plants and dispersers of their seeds, yet their potential in this regard remains overlooked. In general, intraspecific variation in seed-dispersing animals often influences plants through effects of these individual differences on the movement ecology of the dispersers. Two conditions are necessary for individual variation to exert a strong influence on seed dispersal. First, the individual differences in traits should translate into differences in crucial characteristics of seed dispersal. Second, individual variation is more likely to be important when the proportions of particular types of individuals fluctuate strongly in a population or vary across space; when proportions are static, it is less likely that intraspecific differences will be responsible for changes in the dynamics and outcomes of plant–animal interactions. In conclusion, focusing on variation among foraging animals rather than on species averages might bring new, mechanistic insights to the phenomenon of seed dispersal. While this shift in perspective is unlikely to replace the traditional approach (based on the assumption that all important variation occurs among species), it provides a complementary alternative to decipher the enormous variation observed in animal-mediated seed dispersal.
... The greater the difference between these 2 points in space (i.e. higher chromatic contrast), the more conspicuous the object is from the background. Behavioral tests have corroborated the physiologically based predictions of perceptual models in foraging (Cazetta et al. 2009, Behbahaninia et al. 2012) as well as brood-parasitism (Avilés et al. 2010) contexts. ...
Collisions between birds and aircraft (bird strikes) are expensive, risk human lives, and increase bird mortality. Aircraft lighting has been proposed as a potential means of enhancing avian responses to aircraft. Determining the optimal changes to lighting to reduce bird strikes is a complicated problem because avian visual systems differ markedly from that of humans. Icteridae, including Brown-headed Cowbirds (Molothrus ater; hereafter ‘‘cowbirds’’), are involved in bird strikes, have a well-described visual system, and respond to approaching vehicles and lights. Our goal was to assess cowbirds’ responses to a remote-controlled (RC) aircraft fitted with lights tuned to the cowbird eye. On the basis of perceptual modeling (i.e. visual physiology, object and background reflectance, and ambient light conditions), we found that 470-nm lights (‘‘blue’’ portion of the human spectrum) would be the most conspicuous wavelength for cowbirds. We used field experiments to examine cowbird response to 470-nm light treatments. Cowbirds exhibited alert behaviors to a stationary RC aircraft with lights on (both continuous and pulsing) in less than half the time they took to do so with lights off. In response to an approaching RC aircraft, cowbird alert responses were delayed at higher aircraft speeds with the lights off, and we noted a less pronounced speed effect with pulsing lights. However, this interaction effect of aircraft speed and lighting was eliminated with continuous lights. Additionally, higher ambient noise levels delayed cowbirds’ avoidance responses to the RC aircraft, possibly influencing cowbird behavior as a sensory distractor. We suggest that some types of lighting may enhance the birds’ detection and visual tracking of aircraft at high speeds and, thus, holds some potential as a means of reducing the frequency of bird strikes. This sensory-based approach also has implications for management of other bird–object collision problems.
Las colisiones entre aves y aeronaves (choques de aves) son costosas, ponen en riego vidas humanas y aumentan la mortalidad de aves. Se ha propuesto que la iluminaci on de las aeronaves podr´ıa aumentar la respuesta de las aves a las aeronaves. Determinar los cambios que deben hacerse en los sistemas de iluminaci on para reducir los choques con las aves es un problema complejo porque los sistemas visuales de las aves son diferentes del de los humanos. Los Icteridae, incluyendo a Molothrus ater, estan involucrados en los choques con aeronaves, tienen sistemas visuales bien descritos y responden a veh´ıculos y luces que se aproximan. Nuestro objetivo fue evaluar las respuestas de los tordos a una aeronave operada por control remoto equipada con luces sintonizadas con sus ojos. Encontramos que la luz de 470 nm (la parte ‘‘azul’’ del espectro humano) serıa la longitud de onda ma´s conspicua para los tordos, basados en un modelo perceptual (i.e., fisiologıa visual, reflectancia del objeto y del fondo, y propiedades espectrales de la luz). Mediante experimentos de campo examinamos la respuesta de los tordos a los tratamientos de luz de 470 nm. Los tordos mostraron comportamientos de alerta hacia las aeronaves operadas por control remoto con las luces encendidas (tanto continua como parpadeante) en la mitad del tiempo que les llevo para con las aeronaves con las luces apagadas. Las respuestas de alerta de los tordos fueron ma´s lentas hacia aeronaves volando a mayores velocidades con las luces apagadas, pero notamos un efecto menos pronunciado de la velocidad hacia las aeronaves con las luces parpadeantes. Sin embargo, este efecto de la velocidad de la aeronave se elimin ´o con la aeronave con las luces continuas. Adicionalmente, mayores niveles de ruido ambiental demoraron las respuestas de escape hacia las aeronaves operadas por radio control, actuando como una distracci ´on sensorial que posiblemente afecta el comportamiento de los tordos. Sugerimos que algunos tipos de iluminacion pueden aumentar la deteccion por parte de las aves y el seguimiento visual de la aeronave a altas velocidades, y por ende tienen cierto potencial como un modo de reducir la frecuencia de choque entre aeronaves y aves. Esta aproximacion basada en los sistemas sensoriales tambien tiene implicancias para el manejo otras colisiones entre aves y objetos.
... We determined genetic paternity using six microsatellite markers previously developed for the zebra finch [52]. For each locus, we first used a single polymerase chain reaction (PCR) to genotype all parents from the breeding experiment (F 1 males and untreated mothers) to determine the range of allelic diversity for each locus. ...
There is increasing evidence that exposure to stress during development can have sustained effects on animal phenotype and performance across life history stages. For example, developmental stress has been shown to decrease the quality of sexually selected traits (e.g. bird song), and therefore is thought to decrease reproductive success. However, animals exposed to developmental stress may compensate for poor quality sexually selected traits by pursuing alternative reproductive tactics. Here, we examine the effects of developmental stress on adult male reproductive investment and success in the zebra finch (Taeniopygia guttata). We tested the hypothesis that males exposed to developmental stress sire fewer offspring through extra-pair copulations (EPCs), but invest more in parental care. To test this hypothesis, we fed nestlings
corticosterone (CORT; the dominant avian stress hormone) during the nestling period and measured their adult reproductive success using common garden breeding experiments. We found that nestlings reared by
CORT-fed fathers received more parental care compared with nestlings reared by control fathers. Consequently, males fed CORT during development reared nestlings in better condition compared with control males. Contrary to the prediction that developmental stress decreases male reproductive success, we found that CORT-fed males also sired more offspring and were less likely to rear non-genetic offspring compared with control males, and thus had greater overall reproductive success. These data are the first to demonstrate
that developmental stress can have a positive effect on fitness via changes in reproductive success and provide support for an adaptive role of developmental stress in shaping animal phenotype.
Estimating the energy expenditures of wild ungulates in natura often requires an indirect approach splitting them within: (i) basal level, (ii) thermoregulation cost, (iii) feeding cost, (iv) standing and activity cost, (v) growth and reproduction cost. First, each of the costs can be measured (most often through respirometric technics) or estimated (from previously obtained values). Second, these amounts are summed up ("additive" approach) according to the activity budget of the animal. The present bibliographic review only deals with daily expenditures, namely costs (i) to (iv). Various measures (with comparative tables), estimations and [allometric] predictive equations are reported, and their accuracy and limits are discussed. Basal level (without thermoregulation and activity) should be estimated by Standard or Basal Metabolic Rate, but this is difficult to measure on wild animals, even in the laboratory. Other estimations, more or less close to Resting Metabolic Rate (RMR) are therefore often used, although they are less relevant. Kleiber's equation (1961) predicts the standard metabolism of adult animals, mainly mammals and birds, from their body mass; some more accurate models are available but for more limited species, age, sex, ... categories. Thermoregulation is the result of complex interactions between various environmental (air temperature, moisture, wind speed, solar radiation...) and animal (body area, insulation, physiological condition, ...) parameters. Therefore, it is not possible to give more or less standardized costs as for other expenditures. Thermoregulation cost can be considered as null in the so called "Thermoneutral Zone, TNZ". It increases outside this zone because of various physiological, chemical and behavioural mechanisms acting to maintain acceptable deep body temperature. Determining the nature and measuring the cost of the involved mechanisms (which vary according to species, season, age and physical condition of animals) require experiments on trained animals and an heavy experimental device. Qualitative extent to ungulates in natura is somewhat possible, but quantitative extent is difficult. Total feeding cost includes standing and moving (food search) costs, and some more typical costs: "eating" (i.e. prehension, mastication and swallowing), digestion and possibly rumination. In all (domestic or wild) ungulates, the type of food consumed can modify the eating cost, but foraging trips (more or less inversely related to food availability) can obviously involve the most important incremental costs in wild ungulates. Standing and locomotion costs (the main components of activity costs) were quantified in various species by comparing the metabolism of lying, standing and moving animals. From these measures, some authors (particularly Taylor et al., 1982) modeled locomotion cost from body mass. Some estimations of incremental costs due to a difficult terrain (slope, obstacles, snow cover, mud) are also reported. The relevance of the additive approach in energetic studies mainly relies on the quality of the available measures or estimations of each cost and on the accuracy of the activity parameters that are obtained from target animals. Of the various expenditure components, locomotion appears to be the most suitable for comparative purposes; however, the accurate estimation of its cost requires data adequate to identify the right terrain used by the animals.
Evolutionary biologists studying sexually selected bird plumage generally consider this trait to be static throughout a breeding season and assign trait values to individuals on the basis of single measurements. We investigated the propensity for carotenoid-based color of feather patches in male house finches (Carpodacus mexicanus (Muller, 1776)) to change during the breeding period. We recaptured and rescored 63 males and found that the hue of feathers faded significantly over the season. The degree of hue change was a direct function of the amount of time between plumage scores; feathers faded more as the interval between measurements increased. The magnitude of hue change was not, however, related to an individual's age or initial plumage redness, which suggests that certain birds are not more or less prone to fading. Collectively, these findings imply that researchers should more carefully track plumage color expression during the course of a year, as seasonal color shifts may have important consequences for late-season male-male competitive interactions and flexible female mating tactics (e.g., social mate switching, choice of extra-pair partners). Potential mechanisms for this seasonal plumage color shift are discussed.
I compared the mate preferences of female house finches (Carpodacus mexicanus) from populations in which males differ in both plumage coloration and the extent of ventral pigmentation (patch size). Phylogenetic analysis indicated that the small patch of ventral coloration displayed by males in some populations is derived from a larger-patched ancestral state. Regardless of the appearance of males in their own populations, however, females from all populations showed a preference for the most brightly colored males and males with the largest patches. A reduction in patch size independent of a change in female mate preference is not consistent with sensory-bias or reproductive isolation models of sexual selection or with general predictions of runaway models of sexual selection. In contrast, a lack of congruence between female mate preference and male trait expression is predicted by the honest advertisement model, with house finches responding to variation in regional and local access to carotenoid plumage pigments.
A foraging-theory approach, was used to examine consequences of predation for assemblages of desert rodents from North America and the Middle East. In regard to foraging behaviour, desert rodents treat the risk of predation as a cost of foraging. They combine assessments of food and safety to arrive at foraging decisions, exploiting resource patches less intensively in response to increased predatory risk. The cost of predation can be up to 91% of the foraging costs of desert rodents, but the proportion is greater for Middle Eastern rodents than for North American rodents. In regard to community structure, predation can provide the niche axis as well as the necessary trade off for species coexistence. Predation contributes to species coexistence at sites in the Sonoran and Great Basin deserts. But in the Negev Desert, where predation costs are the greatest, predation does not provide a mechanism of species coexistence. In regard to bipedal locomotion, predation most likely confers superior ability to avoid predators by improving sprint speed and ability to take evasive action. The evolution of bipedality will be favoured by situations where the risk of predation is great. -from Authors
Unlearned colour choices by consumers are generally interpreted as an adaptation to avoid unprofitable prey, often involving red warning coloration. However, red colour is a context- dependent stimulus. It signals palatability in ripe fruits, but unlearned fruit colour preferences have rarely been assessed. Therefore, we tested unlearned preferences and the effect of experience on differently coloured artificial fruits in an omnivorous bird. Naïve hand-raised blackcaps (Sylvia atricapilla) preferred red to blue, green, yellow and white artificial fruits, while adult wild-caught birds had no colour preference. In the area from which the experimental birds originated, red ripe fruits are present in 53% of the species with fleshy fruit displays in summer. In these circumstances, unlearned preferences for red might facilitate food recognition in inexperienced fruit-eating birds. Unlearned colour choices should thus be interpreted in a broader context of foraging and not only to explain warning coloration. The contrasting choices of adult and naïve birds imply, however, a low potential for directional selective pressures on fruit colour evolution in this system.
Repeatability is a useful tool for the population geneticist or genetical ecolo-
gist, but several papers have carried errors in its calculation. We outline the correct calcu-
lation of repeatability, point out the common mistake, show how the incorrectly calculated
value relates to repeatability, and provide a method for checking published values and
calculating approximate repeatability values from the F ratio (mean squares among groups/
mean squares within groups).
There is a strong positive correlation between body size of dasyurid marsupials and the mean sizes of their invertebrate prey. This study tests three hypotheses proposed to explain this replationship, using 21 species of dasyurids (body mass range: 5-200 g): 1) the maximum prey size that can be physically handled increases with dasyurid size due to the restricted gapes or forces of biting of smaller dasyurids; 2) the prey size that maximizes rate of energy intake varies with dasyurid size, with animals preferentially consuming the most profitable prey; and 3) prey sizes encountered during foraging vary with dasyurid size. The first hypothesis was rejected. The second and third hypotheses were supported. Individuals of the smaller species maximized rates of energy gain in captivity by feeding preferentially on small prey, and their foraging trails in the field traversed microhabitats where mean potential prey size encountered was small (2-4 mm long). Larger dasyurids preferred large prey, obtained a greater rate of energy gain from them, and foraged in microhabitats where prey lengths averaged ≥6 mm. That larger dasyurids tended to include progressively larger prey in their diets than were available, on average, along their foraging trails, may reflect increasing selectivity for larger prey, but it may also reflect a reduced susceptibility to predation or increased competitive ability for large dasyurids in productive microhabitats, and hence reflect a size-based advantage in encountering large prey. -from Authors
Developmental conditions are known to influence adult phenotypes, including naturally selected traits such as structural size, as well as sexually selected traits such as song and colouration. Biotic environmental factors, e.g., neonatal nutrition and health, are especially known to shape expression of adult traits, but there are fewer investigations on the role of abiotic conditions (e.g., lighting, climate) during the post-natal period. Moreover, the majority of such studies in birds is limited to galliforms and fail to examine sexual signals. We reared mallard (Anas platyrhynchos) drakes under several different husbandry regimes – outdoors with a natural, early-spring photoperiod, or indoors with an artificial, late-spring photoperiod provided by either high-quality or low-quality indoor lights. We tracked growth, moult progress, antioxidant (carotenoid and vitamin A) circulation, and beak colouration (a sexually selected trait) during development and into adulthood. It was found that birds housed outdoors completed moult significantly faster and exhibited more saturated beak colouration at adulthood compared to birds reared indoors under either high or low-quality lighting. Body mass and antioxidant circulation generally did not differ between outdoor-reared birds and those reared indoors on high-quality lighting; however, those reared under high-quality indoor light were heavier than those reared under low-quality light. These results indicate that environmental conditions during ontogeny can impact the development of a sexually attractive phenotype (e.g., faster moult, more colourful bare-parts) in mallards, although the nature of our experimental design does not identify specific causal factors. This finding has implications for the proper husbandry and plumage maintenance of a model avian species.
Summary 1. Fruits are among the most antioxidant-rich foods in nature and thus can be important dietary sources for combating oxidative stress in animals and humans. 2. Because fruits are pigmented by important plant antioxidants such as anthocyanins and caro- tenoids, frugivores may be able to gauge the antioxidant value of a fruit by its colour. However, although the importance of dietary antioxidants and oxidative stress is increasingly being acknow- ledged in evolutionary ecology, it is unknown whether animals can use visual signals to detect the presence of antioxidants in their food. 3. We studied the colour and pigment content of 60 bird-dispersed fruits and used an avian eye model to assess the ability of birds to visually discriminate carotenoid and anthocyanin contents of fruits. We then tested whether the frugivorous European blackcap ( Sylvia atricapilla ) preferentially consumes food containing anthocyanins. 4. Fruit colour variation was explained by variation in anthocyanin contents, and birds were cap- able of discriminating anthocyanin concentrations in fruits based on colour because fruits rich in anthocyanins are black or UV reflecting. However, we found that birds could not use colouration to determine the carotenoid contents of fruits. Ripe fruits contained more anthocyanins than unripe fruits, while there was no difference between ripe and unripe fruits in carotenoid contents. Anthocyanin contents correlated with caloric value in fruits, while there was no such correlation between carotenoids and total energy contents. 5. In food choice experiments, blackcaps selected food containing anthocyanins over food without anthocyanins. 6. In sum, our results indicate that birds actively selected for anthocyanins in their food and that they may use fruit colour as a foraging signal of anthocyanin antioxidant rewards.
Summary • For many species, human-induced disturbances can severely influence an individual's pay-off; however, energy-cost variations from different disturbance types have rarely been reported. • We evaluated the dynamic behavioural responses of staging greater snow geese Anser caerulescens atlanticus to different types of disturbance in southern Quebec, Canada, between 1997 and 2000. We specifically considered the impact of a unique measure, a spring conservation hunt implemented in agricultural habitats in 1999. • We tracked 237 radio-tagged females for 2764 h and recorded 697 take-offs following fortuitous disturbance, scaring and hunting in three regions characterized by different habitats. Geese used cornfields in south-western Quebec, Scirpus marshes and hayfields in the upper St Lawrence estuary, and Spartina marshes and hayfields in the lower estuary. • Overall, disturbance levels increased in the upper and lower estuary during years with hunting, mostly through an increase in hunting and scaring activities. • The probability of geese returning to a refuge after disturbance in agricultural habitats increased in years with hunting except in the corn-growing region. The short-term energy gain of geese resuming feeding after disturbance was less than before disturbance, and this difference was greater in years with hunting. Distances flown after disturbance decreased with flock size and were longer after scaring and hunting than after fortuitous disturbances in the Scirpus region. • Overall, habitat use varied among years and associated estimated energy gain decreased markedly in both years with hunting in the Spartina and corn-growing region, but did not change in the Scirpus region. Changes in behaviour due to disturbance, and especially those associated with hunting, probably contributed to the reduced body condition of staging greater snow geese during years with hunting. • Synthesis and applications. From a methodological viewpoint, we highlight the importance of tracking the behaviour of individual animals after disturbance to properly evaluate its impact. From a conservation perspective, we provide empirical arguments to limit the hunting of breeding waterfowl during their prenuptial migration in order to facilitate their fattening and forthcoming reproduction. From a management standpoint, we suggest that a side-effect of disturbance induced by spring hunting to control overabundant populations may be reduced fattening and breeding output among birds that survive. Together, these data emphasize further the importance of measuring the direct and indirect effects of disturbance rather than assuming effects from the incidence of the disturbance alone. Journal of Applied Ecology (2004) 41, 689–700
Despite the fact that the vast majority of natural prey items are dispersed in a non-random manner, few studies of frequency-dependent
selective predation have explicitly examined the effect of prey dispersion on selectivity. We examined the effect of prey
dispersion on the direction and strength of frequency-dependent selection by wild birds feeding on artificial prey (green
or brown pastry baits). In a series of four experimental manipulations, we tested for the occurrence of frequency dependence
with two different dispersion patterns (random or clumped). Manipulations were carried out at one of two absolute densities
(25 prey m−2 or 100 prey m−2), and were repeated at different sites in Southampton, England and Aljarafe, Spain. Our results suggest that prey dispersion
has no effect on either frequency-dependent or -independent preferences. One possible explanation for this is that the birds
had virtually complete information about prey frequencies at the relatively high densities used and based their preferences
on their overall perception of availability. However, we cannot rule out the possibility that dispersion may influence selectivity
when prey are cryptic or available at lower absolute densities. Although there was no effect of dispersion, frequency-dependent
selection was, overall, significantly anti-apostatic (i.e. rare baits were more preferred than common baits). This anti-apostatic
effect was stronger in Southampton than Aljarafe and stronger at 100 prey m−2 than 25 prey m−2. The differences in the strength of selection between the two locations was interpreted in terms of (i) whether the avian
predators foraged in flocks or not, and (ii) the number of different species present (and, consequently, the variation in
preference among individual birds).
The colors of fruits and flowers are traditionally viewed as an adaptation to increase the detectability of plant organs to
animal vectors. The detectability of visual signals increases with increasing contrasts between target and background. Contrasts
consist of a chromatic aspect (color) and an achromatic aspect (light intensity), which are perceived separately by animals.
To evaluate the relative importance of fruits’ chromatic and achromatic contrasts for the detection by avian fruit consumers
we conducted an experiment with artificial fruits of four different colors in a tropical forest. We displayed the fruits against
two different backgrounds, an artificial background and a natural one, because they differed in achromatic properties. We
found no effect of the type of background on fruit detection rates. Detection rates differed for the four fruit colors. The
probability of detection was explained by the chromatic contrast between fruits and their background, not by the achromatic
contrasts. We suggest that birds attend primarily to chromatic contrast probably because these are more reliably detected
under variable light conditions. Consistent with this hypothesis, we found habitat-specific differences in the conspicuousness
of natural fruit colors in the study area. Fruits of understory species that are subjected to the variable light conditions
within a forest displayed higher chromatic contrasts than species growing in the open restinga forest with constant bright
illumination. There was no such difference for achromatic contrasts. In sum, we suggest that fruit colors differ between habitats
because fruit colors that have strong chromatic contrasts against background can increase plants’ reproductive success, particularly
under variable light conditions.
For many bird species, vision is the primary sensory modality used to locate and assess food items. The health and spectral sensitivities of the avian visual system are influenced by diet-derived carotenoid pigments that accumulate in the retina. Among wild House Finches (Carpodacus mexicanus), we have found that retinal carotenoid accumulation varies significantly among individuals and is related to dietary carotenoid intake. If diet-induced changes in retinal carotenoid accumulation alter spectral sensitivity, then they have the potential to affect visually mediated foraging performance.
In two experiments, we measured foraging performance of house finches with dietarily manipulated retinal carotenoid levels. We tested each bird's ability to extract visually contrasting food items from a matrix of inedible distracters under high-contrast (full) and dimmer low-contrast (red-filtered) lighting conditions. In experiment one, zeaxanthin-supplemented birds had significantly increased retinal carotenoid levels, but declined in foraging performance in the high-contrast condition relative to astaxanthin-supplemented birds that showed no change in retinal carotenoid accumulation. In experiments one and two combined, we found that retinal carotenoid concentrations predicted relative foraging performance in the low- vs. high-contrast light conditions in a curvilinear pattern. Performance was positively correlated with retinal carotenoid accumulation among birds with low to medium levels of accumulation (∼0.5-1.5 µg/retina), but declined among birds with very high levels (>2.0 µg/retina).
Our results suggest that carotenoid-mediated spectral filtering enhances color discrimination, but that this improvement is traded off against a reduction in sensitivity that can compromise visual discrimination. Thus, retinal carotenoid levels may be optimized to meet the visual demands of specific behavioral tasks and light environments.
Inferences about mechanisms at one particular stage of a visual pathway may be made from psychophysical thresholds only if the noise at the stage in question dominates that in the others. Spectral sensitivities, measured under bright conditions, for di-, tri-, and tetrachromatic eyes from a range of animals can be modelled by assuming that thresholds are set by colour opponency mechanisms whose performance is limited by photoreceptor noise, the achromatic signal being disregarded. Noise in the opponency channels themselves is therefore not statistically independent, and it is not possible to infer anything more about the channels from psychophysical thresholds. As well as giving insight into mechanisms of vision, the model predicts the performance of colour vision in animals where physiological and anatomical data on the eye are available, but there are no direct measurements of perceptual thresholds. The model, therefore, is widely applicable to comparative studies of eye design and visual ecology.
Fruit color changes during ripening are typically viewed as an adaptation to increase signal efficacy to seed dispersers. Plants can increase signal efficacy by enhancing chromatic (wavelength related) and/or achromatic (intensity related) contrasts between fruit and background. To assess how these contrasts determine the detectability of fruit signals, we conducted 2 experiments with free-flying crows (Corvus ossifragus) under seminatural conditions in a 2025 m-super-2 aviary. Crows searched first for artificial red and black fruits and detected red fruits from a larger distance. Because artificial red fruits had higher chromatic and lower achromatic contrasts against foliage than artificial black fruits, crows apparently prioritized chromatic contrasts. Thus, the common change in fruit color from red to black during ripening does not increase signal efficacy to crows. In a second trial, crows searched for UV-reflecting and black blueberries (Vaccinum myrtillus) against backgrounds of foliage and sand. Against foliage, UV-reflecting berries had higher chromatic and achromatic contrasts than black berries, and crows detected them from a larger distance. Against sand, UV-reflecting berries had low achromatic contrasts and black berries low chromatic contrasts. Crows detected both fruit types equally, suggesting that they used chromatic contrasts to detect UV-reflecting berries and achromatic contrasts to detect black berries. Birds prioritized chromatic contrasts when searching for artificial red fruits in foliage but not when searching for blueberries on sand. We suggest that the relative importance of chromatic and achromatic contrasts is contingent on the chromatic and achromatic variance of the background. Models of signal perception can be improved by incorporating background-specific effects. Copyright 2006.
The costs of developing, maintaining, and activating the immune system have been cited as an important force shaping life-history evolution in animals. Immunological defenses require energy, nutrients and time that might otherwise be devoted to other life-history traits like sexual displays or reproduction. Carotenoid pigments in animals provide a unique opportunity to track the costs of immune activation, because they are diet-derived, modulate the immune system, and are used to develop colorful signals of quality. Carotenoids also accumulate in the retinas of birds, where they tune spectral sensitivity and provide photoprotection. If carotenoid accumulation in the retina follows the patterns of other tissues, then immune activation may deplete retinal carotenoid levels and impact visual health and function. To test this hypothesis, we challenged molting wild-caught captive house finches (Carpodacus mexicanus) with weekly injections of lipopolysaccharide (LPS) and phytohaemagglutinin (PHA) over the course of 8 weeks. Immunostimulated adult males and females produced significant antibody responses and molted more slowly than uninjected control birds. After 8 weeks, immune-challenged birds had significantly lower levels of specific retinal carotenoid types (galloxanthin and zeaxanthin), but there were no significant differences in the plasma, liver or feather carotenoid levels between the treatment groups. These results indicate that immune-system activation can specifically deplete retinal carotenoids, which may compromise visual health and performance and represent an additional somatic and behavioral cost of immunity.
A large variety of predatory species rely on their visual abilities to locate their prey. However, the search for prey may be hampered by prey camouflage. The most prominent example of concealing coloration is background-matching prey coloration characterized by a strong visual resemblance of prey to the background. Even though this principle of camouflage was recognized to efficiently work in predator avoidance a long time ago, the underlying mechanisms are not very well known. In this study, we assessed whether blue tits (Cyanistes caeruleus) use chromatic cues in the search for prey. We used two prey types that were achromatically identical but differed in chromatic properties in the UV/blue range and presented them on two achromatically identical backgrounds. The backgrounds had either the same chromatic properties as the prey items (matching combination) or differed in their chromatic properties (mismatching combination). Our results show that birds use chromatic cues in the search for mismatching prey, whereupon chromatic contrast leads to a 'pop-out' of the prey item from the background. When prey was presented on a matching background, search times were significantly higher. Interestingly, search for more chromatic prey on the matching background was easier than search for less chromatic prey on the matching background. Our results indicate that birds use both achromatic and chromatic cues when searching for prey, and that the combination of both cues might be helpful in the search task.
It has been suggested that the major advantage of trichromatic over dichromatic colour vision in primates is enhanced detection of red/yellow food items such as fruit against the dappled foliage of the forest. This hypothesis was tested by comparing the foraging ability of dichromatic and trichromatic Geoffroy's marmosets (Callithrix geoffroyi) for orange- and green-coloured cereal balls (Kix) in a naturalized captive setting. Trichromatic marmosets found a significantly greater number of orange, but not green, Kix than dichromatic marmosets when the food items were scattered on the floor of the cage (at a potential detection distance of up to 6 m from the animals). Under these conditions, trichromats but not dichromats found significantly more orange than green Kix, an effect that was also evident when separately examining the data from the end of the trials, when the least conspicuous Kix were left. In contrast, no significant differences among trichromats and dichromats were seen when the Kix were placed in trays among green wood shavings (detection distance < 0.5 m). These results support an advantage for trichromats in detecting orange-coloured food items against foliage, and also suggest that this advantage may be less important at shorter distances. If such a foraging advantage for trichromats is present in the wild it might be sufficient to maintain the colour vision polymorphism seen in the majority of New World monkeys.
Differences in growth conditions during early life have been suggested to cause long-lasting effects on morphology and quality of adult birds. We experimentally investigated the effect of early growth conditions on the expression of sexual ornaments later in life in male ring-necked pheasants (Phasianus colchicus). We also investigated the effects on immune function, as it could be a functional link between early nutrition and ornament expression. We manipulated the dietary protein intake during the first eight weeks post hatching. Males receiving fodder with 27% protein during the first three weeks of life grew larger and more colourful wattles when sexually mature than males receiving a low-protein diet (20.5% protein). Spur length was unaffected by diet treatment. Manipulation of food protein levels during weeks 4-8 after hatching had no effect on the development of ornaments. The different protein treatments had no long-term effect on either humoral or cell-mediated immune responses. There was, however, a positive relationship between spur length and cell-mediated immune responsiveness. Our study shows that expression of a sexual ornament in adult pheasants reflects nutritional conditions early in life. Because the expression of secondary sexual ornaments is affected by conditions during early growth, by selecting more ornamented males, females would choose mates that are superior at handling early nutritional stress. If the susceptibility to early nutritional stress also has a hereditary basis, females may benefit by obtaining 'good genes'.
In most animals, the origins of mating preferences are not clear. The "sensory-bias" hypothesis proposes that biases in female sensory or neural systems are important in triggering sexual selection and in determining which male traits will become elaborated into sexual ornaments. Subsequently, other mechanisms can evolve for discriminating between high- and low-quality mates. Female guppies (Poecilia reticulata) generally show a preference for males with larger, more chromatic orange spots. It has been proposed that this preference originated because it enabled females to obtain high-quality mates. We present evidence for an alternative hypothesis, that the origin of the preference is a pleiotropic effect of a sensory bias for the colour orange, which might have arisen in the context of food detection. In field and laboratory experiments, adult guppies of both sexes were more responsive to orange-coloured objects than to objects of other colours, even outside a mating context. Across populations, variation in attraction to orange objects explained 94% of the inter-population variation in female mate preference for orange coloration on males. This is one of the first studies to show both an association between a potential trigger of a mate-choice preference and a sexually selected trait, and also that an innate attraction to a coloured inanimate object explains almost all of the observed variation in female mate choice. These results support the "sensory-bias" hypothesis for the evolution of mating preferences.
Early nutrition has recently been shown to have pervasive, downstream effects on adult life-history parameters including lifespan, but the underlying mechanisms remain poorly understood. Damage to biomolecules caused by oxidants, such as free radicals generated during metabolic processes, is widely recognized as a key contributor to somatic degeneration and the rate of ageing. Lipophilic antioxidants (carotenoids, vitamins A and E) are an important component of vertebrate defences against such damage. By using an avian model, we show here that independent of later nutrition, individuals experiencing a short period of low-quality nutrition during the nestling period had a twofold reduction in plasma levels of these antioxidants at adulthood. We found no effects on adult external morphology or sexual attractiveness: in mate-choice trials females did not discriminate between adult males that had received standard- or lower-quality diet as neonates. Our results suggest low-quality neonatal nutrition resulted in a long-term impairment in the capacity to assimilate dietary antioxidants, thereby setting up a need to trade off the requirement for antioxidant activity against the need to maintain morphological development and sexual attractiveness. Such state-dependent trade-offs could underpin the link between early nutrition and senescence.
Six groups of organically fed hens were studied for egg production, feed parameters, and egg quality from 20 to 31 wk of age. Treatments were 3 diets (0, 15, and 25% blue lupin) with or without supplements of foraging material (whole carrots and corn silage). Increased lupin content increased nonstarch polysaccharides content and reduced methionine content below the hens' requirement. Egg production at 31 wk was lower with the 25% lupin diet without (69%) and with foraging material (76%) compared with the other diets (approximately 90%). Egg weight was highest with the 0% lupin diet (64 g), and 15% lupin diet (60 g), whereas the 25% lupin diet without and with foraging material resulted in egg weights of 58 and 56 g, respectively. Feed intakes were approximately 113 g of diet/ hen per d and 113 g of supplement/hen per d in 0 and 15% lupin treatments, respectively. Feeding the 25% lupin diet significantly reduced diet intake to approximately 91 g, and increased supplement intake to 118 g for the treatment with foraging material. Eggs from treatments with foraging material had significantly higher sulfur-like aftertaste in sensory evaluation. Yolk color became significantly lighter and more yellow with lupin content, but darker and less greenish with foraging material. Increased lupin levels decreased albumen DM, whereas foraging material had no effect. Inclusion of 25% lupin in layer diets is only recommended when supplying some methionine source, as egg production and quality parameters are dramatically impaired. However, supplement of foraging material significantly improves egg production.
American water shrews (Sorex palustris) are aggressive predators that feed on a variety of terrestrial and aquatic prey. They often forage at night, diving into streams and ponds in search of food. We investigated how shrews locate submerged prey using high-speed videography, infrared lighting, and stimuli designed to mimic prey. Shrews attacked brief water movements, indicating motion is an important cue used to detect active or escaping prey. They also bit, retrieved, and attempted to eat model fish made of silicone in preference to other silicone objects showing that tactile cues are important in the absence of movement. In addition, water shrews preferentially sniffed model prey fish and crickets underwater by exhaling and reinhaling air through the nostrils, suggesting olfaction plays an important role in aquatic foraging. The possibility of echolocation, sonar, or electroreception was investigated by testing for ultrasonic and audible calls above and below water and by presenting electric fields to foraging shrews. We found no evidence for these abilities. We conclude that water shrews detect motion, shape, and smell to find prey underwater. The short latency of attacks to water movements suggests shrews may use a flush-pursuit strategy to capture some prey.
• insectivore
• olfaction
• somatosensory
• tactile
• whiskers
Nests of altricial birds exhibit variable spectral properties that may affect the efficacy (conspicuousness) of the colored begging traits that a nestling displays to its parents. Here we explored whether selection for efficient perception has favored the evolution of nestling color designs that maximizes nestling detectability in variable light environments. Visual models were used to estimate how parents perceive the coloration of mouths, flanges, heads, and breasts of nestlings within their nest in 21 species of European birds. We show that the largest chromatic and achromatic contrasts against the nest background appeared for nestling mouths and flanges, respectively. Nestlings of open-nesting species showed a larger general achromatic contrast with the nest than did nestlings of hole-nesting species. However, nestlings of hole nesters showed a more evident achromatic contrast between flanges and other traits than did nestlings of open nesters. In addition, species with larger clutch sizes showed larger general achromatic contrasts with the nest. Gaping traits of open-nesting species contrasting with the nest background were better perceived under rich light regimes than under poor ones. These findings are consistent with a scenario in which selection for nestling detectability in dark environments has favored the evolution of particular achromatic components of gape coloration but also nestling traits that enhance signal efficacy by maximizing color contrasts within a nestling.
Inferences about mechanisms at one particular stage of a visual pathway may be made from psychophysical thresholds only if the noise at the stage in question dominates that in the others. Spectral sensitivities, measured under bright conditions, for di-, tri-, and tetrachromatic eyes from a range of animals can be modelled by assuming that thresholds are set by colour opponency mechanisms whose performance is limited by photoreceptor noise, the achromatic signal being disregarded, Noise in the opponency channels themselves is therefore not statistically independent, and it is not possible to infer anything more about the channels from psychophysical thresholds. As well as giving insight into mechanisms of vision, the model predicts the performance of colour vision in animals where physiological and anatomical data on the eye are available, but there are no direct measurements of perceptual thresholds. The model, therefore, is widely applicable to comparative studies of eye design and visual ecology.
Estimating the energy expenditures of wild ungulates in natura often requires an indirect approach splitting them within: (i) basal level, (ii) thermoregulation cost, (iii) feeding cost, (iv) standing and activity cost, (v) growth and reproduction cost. First, each of the costs can be measured (most often through respirometric technics) or estimated (from previously obtained values). Second, these amounts are summed up ("additive" approach) according to the activity budget of the animal. The present bibliographic review only deals with daily expenditures, namely costs (i) to (iv). Various measures (with comparative tables), estimations and [allometric] predictive equations are reported, and their accuracy and limits are discussed. Basal level (without thermoregulation and activity) should be estimated by Standard or Basal Metabolic Rate, but this is difficult to measure on wild animals, even in the laboratory. Other estimations, more or less close to Resting Metabolic Rate (RMR) are therefore often used, although they are less relevant. Kleiber's equation (1961) predicts the standard metabolism of adult animals, mainly mammals and birds, from their body mass; some more accurate models are available but for more limited species, age, sex,... categories. Thermoregulation is the result of complex interactions between various environmental (air temperature, moisture, wind speed, solar radiation...) and animal (body area, insulation, physiological condition,...) parameters. Therefore, it is not possible to give more or less standardized costs as for other expenditures. Thermoregulation cost can be considered as null in the so called "Thermoneutral Zone, TNZ". It increases outside this zone because of various physiological, chemical and behavioural mechanisms acting to maintain acceptable deep body temperature. Determining the nature and measuring the cost of the involved mechanisms (which vary according to species, season, age and physical condition of animals) require experiments on trained animals and an heavy experimental device. Qualitative extent to ungulates in natura is somewhat possible, but quantitative extent is difficult. Total feeding cost includes standing and moving (food search) costs, and some more typical costs: "eating" (Le. prehension, mastication and swallowing), digestion and possibly rumination. In all (domestic or wild) ungulates, the type of food consumed can modify the eating cost, but foraging trips (more or less inversely related to food availability) can obviously involve the most important incremental costs in wild ungulates. Standing and locomotion costs (the main components of activity costs) were quantified in various species by comparing the metabolism of lying, standing and moving animals. From these measures, some authors (particularly Taylor et al., 1982) modeled locomotion cost from body mass. Some estimations of incremental costs due to a difficult terrain (slope, obstacles, snow cover, mud) are also reported.
The eastern race of Carpodacus mexicanus tolerates low winter temperatures very poorly. Their metabolism and cold tolerance is, at least partically, a function of food composition. Evolution of larger bill size in the eastern race of house finch may be due to preference for sunflower seeds at bird feeders in winter, increased cold tolerance as a result of this choice, and the increased range of permanent residency of this species. -from Authors
The House Finch is among the most mundane birds, so ubiquitous and familiar across the U.S. and Canada that it does not rate a glance from most bird enthusiasts. But males have carotenoid-based plumage coloration that varies markedly among individuals, making the House Finch a model species for studies of the function and evolution of colorful plumage. In more depth and detail than has been attempted for any species of bird, this book takes a tour of the hows and whys of ornamental plumage coloration. The book begins by reviewing the history of the study of colorful plumage, which began in earnest with the debates of Darwin and Wallace but which was largely forgotten by the middle of the 20th century. Documenting the extensive plumage variation among males both within and between populations of House Finches, the book explores the mechanisms behind plumage variation and looks at the fitness consequences of condition-dependent ornament display for both males and females. The book concludes by examining the processes by which carotenoid-based ornamental coloration may have evolved.
Spectral profiles of intact carotenoid-bearing feathers and of pigments isolated from polls and breasts of Common and Hoary redpolls (Carduelis flammea and C. hornemanni) were compared to help clarify the taxonomic relationship of the two taxa. Pigments were identified by thin-layer chromatography and by partitioning experiments. Two carotenoids were present in all samples, apparently echinenone and lutein. Color differences between taxa result from differences in absolute concentrations and changes in the relative concentration of the two pigments. Orange feathers have relatively high concentrations of lutein. Pigments are restricted to feather rami. Those most intensely colored (from polls) have flattened rami and lack barbules. New breast feathers are tipped with an unpigmented band. During late winter the band becomes worn exposing the colored rami. The most intensely pigmented breast feathers (usually those of Common Redpolls) lose their barbules as spring and summer progress.
The effects of age, sex and previous experience on colour avoidance in northern bobwhites, Colinus virginianus, were evaluated. First, unlearned colour preferences were determined by measuring pecking by 52 1-day-old bobwhite chicks at pinheads of four colours. The number of first pecks and the total number of pecks varied significantly among colours (P=0.011 and P<0.001, respectively). Both measures showed that the descending order of preference was blue>green>yellow>red. There were no clear sex differences in pecking preference. A second experiment used a two-cup avoidance test to evaluate the effects of sex and previous experience on avoidance of coloured grain by juvenile bobwhite. Forty 11-week-old birds were pre-exposed for 7 days to either multi-coloured or undyed food, and then tested for 5 days for avoidance of red or blue food. Red food was avoided relative to undyed food (preference ratio=0.426, P=0.004), whereas blue food was not avoided. Sex of bird, pre-exposure to coloured food, and day of test had no significant effect on colour avoidance. Finally, 26 of the same birds were retested at the age of 31 weeks for avoidance of blue and red food. Results indicated no change in colour avoidance with age. Although these experiments failed to replicate a sex difference in colour avoidance that we found in a previous study, they did demonstrate that bobwhites show an unlearned aversion to red which is persistent and resistant to extinction. Because red is a common warning colour in insects, this aversion may be an adaptation for avoiding aposematically coloured prey. (C) 1995 The Association for the Study of Animal Behaviour
The effects of age, sex and previous experience on colour avoidance in northern bobwhites,Colinus virginianus, were evaluated. First, unlearned colour preferences were determined by measuring pecking by 52 1-day-old bobwhite chicks at pinheads of four colours. The number of first pecks and the total number of pecks varied significantly among colours (P=0·011 andPgreen>yellow>red. There were no clear sex differences in pecking preference. A second experiment used a two-cup avoidance test to evaluate the effects of sex and previous experience on avoidance of coloured grain by juvenile bobwhite. Forty 11-week-old birds were pre-exposed for 7 days to either multi-coloured or undyed food, and then tested for 5 days for avoidance of red or blue food. Red food was avoided relative to undyed food (preference ratio=0·426,P=0·004), whereas blue food was not avoided. Sex of bird, pre-exposure to coloured food, and day of test had no significant effect on colour avoidance. Finally, 26 of the same birds were retested at the age of 31 weeks for avoidance of blue and red food. Results indicated no change in colour avoidance with age. Although these experiments failed to replicate a sex difference in colour avoidance that we found in a previous study, they did demonstrate that bobwhites show an unlearned aversion to red which is persistent and resistant to extinction. Because red is a common warning colour in insects, this aversion may be an adaptation for avoiding aposematically coloured prey.
Starlings that were feeding nestlings collected mealworms from an artificial feeder where the cumulative number of prey was a logarithmic function of patch residence time (Tp). The patch was placed at various locations 8-600m away from the nests. The number of prey swallowed, Tp, and number delivered to the young was recorded. Four models of optimal Tp are discussed: 1) Maximize YIELD: energy collected per total round trip time (including time in the nest); 2) Maximize rate of DELIVERY: YIELD minus parent's metabolism; 3) Maximize FAMILY GAIN: DELIVERY minus brood's metabolism, considering the energy cost of begging by the chicks; 4) Maximize EFFICIENCY: YIELD/parent's metabolism - relevant when there is a cost in spending energy (eg due to constraints in maximum rate of heat dissipation). Results differ significantly from the YIELD and EFFICIENCY models. The FAMILY GAIN model gives the best fit to the data. The variance in Tp reflects the cost of deviations from the optimum. The frequency distribution of observed Tp resembled the predictions of a descriptive model (PROFITABILITY MATCHING) based on proportional alocation of effort to various behavioural options depending on their relative pay- off. Manipulations in brood size resulted in different allocation of food between parent and young but did not affect overall Tp. - Author
The global prevalence of red and black fruits has still not been explained. Hypotheses based on innate consumer preferences have been tested and rejected. Though colour itself plays an important role in animal foraging, it is only one component of signals. Another major component are colour contrasts against background achieving the conspicuousness of signals. In order to evaluate which signal component determines consumers behaviour, we measured fruit colour and colour contrasts of 43 species against their natural background under ambient light conditions. Red and black fruits exhibit stronger contrasts and are therefore more conspicuous to consumers than fruits of other colours. Subsequently, trials were carried out to determine whether colour or conspicuousness influences avian food choice. Four bird species strongly preferred contrasting red–green or black–green over uni-coloured red, green, or black fruit displays, while no preference for particular hues was found. We therefore hypothesize that conspicuousness determines avian food selection and define the contrast hypothesis: Diurnal dispersers select fruit colours based on their conspicuousness and not their colour itself.Because colour vision is an ancient trait, the entire heterogeneous group of frugivorous birds most likely perceives conspicuousness uniformly over evolutionary time spans. Conspicuousness has thus the potential to explain the global prevalence of red and black fruits.
Abstract 1. Conspicuous body colouration is counter-intuitive in stationary predators because sit-and-wait tactics frequently rely on concealed traps to capture prey. Consequently, bright colours and contrasting patterns should be rare in predators using traps as they may alert potential prey. Yet, some orb-weaving spiders are brightly coloured and contrastingly patterned. How can conspicuousness of trap-building sit-and-wait predators be favoured by natural selection?
2. Observations of spiny spiders Gasteracantha fornicata in north-eastern Australia showed that the size of spiders relative to their orb webs correlated positively with relative prey numbers already captured in their webs. A possible explanation is that the relatively larger appearance of the yellow–black striped dorsal surface of this spider attracts more visually oriented prey items. Prey attracted to webs may get trapped, thereby increasing the spiders' foraging success.
3. To test this hypothesis for the function of conspicuous body colouration, a field experiment was conducted that documented the prey capture rates of spiny spiders after manipulating or sham-manipulating their appearance.
4. As predicted, spiders that were dyed black on their striped dorsal surface caught relatively fewer prey items than did control spiders. Thus, conspicuous dorsal body colouration may be adaptive in spiny spiders because it increases foraging success and, presumably, survival rates and reproductive outputs. Overall, these data support the colour-as-prey-attractant hypothesis in a stationary, trap-building predator.
Summary • Carotenoids are micronutrients with many beneficial health-related effects. They are effective antioxidants and stimulants of the immune system. Carotenoids cannot be synthesized in animals and must be obtained from food. As such, they may limit reproductive output and performance, and on the proximate level mediate reproductive trade-offs. • We studied carotenoid limitation in wild Great Tits (Parus major) by supplementing prelaying and laying females with lutein, the most abundant carotenoid in this species. We followed the effects of this supplementation on egg yolk carotenoid composition, and offspring and parental performance. • Females transferred the supplemented lutein into egg yolks, increasing lutein concentration to the upper limit of naturally occurring concentrations in control pairs. Concentrations of zeaxanthin, β-carotene and α-carotene did not differ between supplemented and control pairs. • Effects on offspring and parental performance were generally absent or weak. There were no effects on timing of laying, clutch size, hatching success, nestling survival, nestling mass (day 6 and 14), tarsus length or T-cell mediated immune response. Males on supplemented nests fed their young more than those on control nests. There was no positive effect on female feeding or mass. • Negligible effects of lutein supplementation on offspring and parental performance might be explained by high natural abundance of carotenoids or other antioxidants, where additional carotenoids bear no strong advantage to the birds. Additionally, conflicting results of different studies may be explained by species-specific features of their life-histories. Functional Ecology (2007) 21, 776–783doi: 10.1111/j.1365-2435.2007.01277.x
Although homeotherms likely experience costs of both predation risk and thermoregulation while foraging, it is unclear how foragers contend with these costs. We used foraging trays placed in sheltered microsites to determine whether temperature, a direct cue of predator presence (predator urine) and an indirect cue of predation risk (cloudy nights) affect foraging of white-footed mice, Peromyscus leucopus, in winter. Mice were presented with urine from bobcats, Lynx rufus, red foxes, Vulpes vulpes, and coyotes, Canis latrans, an herbivore (whitetailed deer, Odocoileus virginianus), and a water control. To measure rodent foraging, we used seeds of millet mixed with sand to quantify giving-up densities (the number of seeds left in each foraging tray). Giving-up density was not affected by predator urine. Rather, rodent foraging was affected by an interaction of temperature and weather. On overcast nights, when predation risk was likely lower, mice foraged more when soil temperature was higher, presumably reducing thermoregulatory costs. On clear nights, foraging was low regardless of soil temperature, presumably because foraging was more risky. These results suggest that mice consider thermoregulatory costs and predation risk when making foraging decisions, and that the indirect cue afforded by weather, rather than the direct cue of predator urine, is among the cues used to make foraging decisions. Moreover, these results suggest that sensitivity to a particular cue is likely to be context-dependent.
Food color can be indicative of specific nutrients, and thus discrimination based on color can be a valuable foraging behavior. Several bird and fish species with carotenoid-based body ornamentation show color preferences for presumably carotenoid-rich red and orange foods. However, little is known within species about whether or not individuals with (or growing) more colorful ornaments show stronger food-color preferences than those with drabber coloration. Here, we examine food color preferences in house finches (Carpodacus mexicanus) – a species with sexually dichromatic and selected carotenoid coloration – as a function of sex and plumage coloration during molt. We captured wild, molting juvenile house finches over 4 wk in late summer/early fall, quantified the color and size of plumage ornaments being developed in males, and determined food color preference in captivity by presenting individuals with dyed sunflower chips (red, orange, yellow, and green). On average, finches showed an aversion to yellow-dyed chips and a preference for red- and green-colored chips. We found no significant difference between male and female preferences for specific food colors, and food color preference was not significantly related to male plumage ornamentation. However, we did find that redder birds demonstrated a higher degree of food selectivity, measured as the proportion of their preferred food color consumed. These results suggest that food color is not a major factor determining food choice in molting house finches, but that there still may be aspects of foraging behavior that are linked to the development of colorful plumage.
Under the indicator models of mate choice, female preferences evolve to exploit the condition-dependence or "indicator value" of male traits, which in turn may cause these traits to evolve to elaborate extremes. If the indicator value of a male trait changes, the payoff function of the female preference for that trait should change and the preference should evolve to a new optimum. I tested this prediction in the guppy, Poecilia reticulata, a species in which the indicator value of a sexually selected male trait, carotenoid coloration, varies geographically. Carotenoid coloration is thought to be an indicator of foraging ability and health because animals must obtain carotenoid pigments from their diet. The primary dietary source of carotenoids for guppies is unicellular algae, the abundance of which varies among natural streams because of variation in forest canopy cover. Carotenoid availability limits male coloration to a greater extent in streams with greater forest canopy cover. Thus, the indicator value of male coloration covaries positively with canopy cover. To test the indicator model prediction, I measured genetic divergence in the strength of female preferences for carotenoid coloration between high- and low-carotenoid availability streams in each of three river drainages. Second-generation laboratory-born females were given a choice between full-sib males raised on three different dietary levels of carotenoids. For all six populations, male attractiveness (as determined from the responses of females to male courtship displays) increased with dietary carotenoid levels. However, the strength of female preferences differed between populations in the predicted direction in only one of three river drainages. These results fail to support a crucial prediction of the indicator model. More studies taking an interpopulation approach to studying mate preference evolution are needed before the explanatory value of the indicator models can be rigorously assessed.
Gull-billed terns (Gelochelidon nilotica) were video-filmed while searching for and capturing fiddler crabs. Search consists of a vertical head nystagmus, with fast
upward flicks and downward slow phases made at the angular speed of the substrate in the approximate direction of the bill.
The bill points down at about 60° during hunting, but is brought up to 15° from time to time, which brings the visual streak
into line with the horizon; 45° roll movements of the head are consistent with alternation between the use of the temporal
and central foveas to view the same object. When a crab has been detected the nystagmus is suspended, and the tern tracks
the crab continuously as it manoeuvres into a catching position. This may involve tucking the head under the body so that
the bill is 45° behind the vertical, and flying up and backwards for some metres, straightening up the head at the same time.
Solitary predators respond to cryptic prey by adopting counterstrategies such as forming a search image or reducing their search rate. However, the response of group-foraging individuals to cryptic prey remains poorly studied. We investigated the effect of the presence of an experienced or a naïve conspecific on the ability of nutmeg mannikins, Lonchura punctulata, to exploit millet seeds presented on cryptic and noncryptic backgrounds. The conspecific's level of experience did not affect a focal bird's foraging, so we lumped both experience condition for analysis. The presence of a competitor tended to increase the occurrences of vigilance and food searching, but it did not affect the duration of vigilance. In contrast, foraging on a cryptic background significantly affected foraging by reducing the occurrences of food searching and vigilance, and increasing the latency to eat the first seed as well as the number of detection errors. Background type and competitor presence interacted significantly for searching bout duration, number of seeds eaten and foraging efficiency. In all cases, competitor presence negatively affected foraging efficiency under cryptic backgrounds. Finally, the foraging efficiency of individuals that had previously foraged with a competitor on cryptic seeds remained low even after the competitor had been removed. Thus, costs of foraging on cryptic prey may be greater for social foragers than for solitary foragers.
Abstract. Thesis (M.S.)--Auburn University, 1997. Vita. Includes bibliographical references (leaves 23-29).
There is a growing body of data on avian eyes, including measurements of visual pigment and oil droplet spectral absorption, and of receptor densities and their distributions across the retina. These data are sufficient to predict psychophysical colour discrimination thresholds for light-adapted eyes, and hence provide a basis for relating eye design to visual needs. We examine the advantages of coloured oil droplets, UV vision and tetrachromacy for discriminating a diverse set of avian plumage spectra under natural illumination. Discriminability is enhanced both by tetrachromacy and coloured oil droplets. Oil droplets may also improve colour constancy. Comparison of the performance of a pigeon's eye, where the shortest wavelength receptor peak is at 410 nm, with that of the passerine Leiothrix, where the ultraviolet-sensitive peak is at 365 nm, generally shows a small advantage to the latter, but this advantage depends critically on the noise level in the sensitivity mechanism and on the set of spectra being viewed.
The visual receptors of the passeriform bird Serinus canaria, the canary, have been examined microspectrophotometrically and the sequences of the opsins determined. Rods have a maximum absorbance (lambda max) at 506 nm. Four spectral classes of single cone are present: long-wave-sensitive (LWS) containing a photopigment with lambda max at 569 nm, middle-wave-sensitive (MWS) with lambda max at 505 nm, short-wave-sensitive (SWS) with lambda max at 442 nm, and ultraviolet-sensitive (UVS) with lambda max at about 366 nm. Double cones possess the 569-nm pigment in both members. Typical combinations of photopigment and oil droplet occur in most cone classes. An ambiguity exists in the oil droplet of the single LWS cones. In some birds, LWS cones are paired with an R-type droplet, whereas in the majority of canaries the LWS pigment is paired with a droplet similar to the P-type of double cones. Mechanisms of spectral tuning within each opsin class are discussed.
Reef fishes present the observer with the most diverse and stunning assemblage of animal colours anywhere on earth. The functions of some of these colours and their combinations are examined using new non-subjective spectrophotometric measurements of the colours of fishes and their habitat. Conclusions reached are as follows: (i) the spectra of colours in high spatial frequency patterns are often well designed to be very conspicuous to a colour vision system at close range but well camouflaged at a distance; (ii) blue and yellow, the most frequently used colours in reef fishes, may be good for camouflage or communication depending on the background they are viewed against; and (iii) reef fishes use a combination of colour and behaviour to regulate their conspicuousness and crypsis.
Under the indicator models of mate choice, female preferences evolve to exploit the condition-dependence or "indicator value" of male traits, which in turn may cause these traits to evolve to elaborate extremes. If the indicator value of a male trait changes, the payoff function of the female preference for that trait should change and the preference should evolve to a new optimum. I tested this prediction in the guppy, Poecilia reticulata, a species in which the indicator value of a sexually selected male trait, carotenoid coloration, varies geographically. Carotenoid coloration is thought to be an indicator of foraging ability and health because animals must obtain carotenoid pigments from their diet. The primary dietary source of carotenoids for guppies is unicellular algae, the abundance of which varies among natural streams because of variation in forest canopy cover. Carotenoid availability limits male coloration to a greater extent in streams with greater forest canopy cover. Thus, the indicator value of male coloration covaries positively with canopy cover. To test the indicator model prediction, I measured genetic divergence in the strength of female preferences for carotenoid coloration between high- and low-carotenoid availability streams in each of three river drainages. Second-generation laboratory-born females were given a choice between full-sib males raised on three different dietary levels of carotenoids. For all six populations, male attractiveness (as determined from the responses of females to male courtship displays) increased with dietary carotenoid levels. However, the strength of female preferences differed between populations in the predicted direction in only one of three river drainages. These results fail to support a crucial prediction of the indicator model. More studies taking an interpopulation approach to studying mate preference evolution are needed before the explanatory value of the indicator models can be rigorously assessed.
Recent research has highlighted the extent to which birds utilise ultraviolet vision in mate choice and foraging. However, neither the importance of the ultraviolet compared with other regions of the visual spectrum nor the use of wavelength cues in other visual tasks have been explored. We assessed the individual choices of zebra finches (Taeniopygia guttata) for different-coloured seeds (red and white millet) under lighting conditions in which filters selectively removed blocks of the avian-visible spectrum corresponding to the spectral sensitivity of the four retinal cone types that subserve colour vision in this species. The effects corresponded to those predicted from the calculated distances between seed types, and between each seed type and the background, in a simple model of tetrachromatic colour space. As predicted for this foraging task, the removal of long-wavelength information had a greater influence than the removal of shorter wavelengths, including ultraviolet wavelengths. These results have important implications for predator-prey interactions and suggest that future studies of natural foraging should consider variations in the light environment.
Birds of California in relation to fruit industry
- Beal
Beal, F.E.L. (1907). Birds of California in relation to fruit industry. US Dept. Agric. Biol. Surv. Bull., 30, 13-23
Competing for resources
- Milinski
Milinski, M. & Parker, G.A. (1991). Competing for resources. In J.R. Krebs & N.B. Davies (Eds),
Behavioural ecology: an evolutionary approach (pp. 167-168). Oxford: Blackwell Publishing.
A red bird in a brown bag: the function and evolution of ornamental plumage coloration in the house finch
- G E Hill
Hill, G.E. (2002). A red bird in a brown bag: the function and evolution of ornamental plumage
coloration in the house finch. New York, NY: Oxford University Press.