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Abstract

Eyes convey important information about the external and internal worlds of animals. Individuals can follow the gaze of others to learn about the location of salient objects as well as assess eye qualities to evaluate the health, age or other internal states of conspecifics. Because of the increasing prevalence of artificial lighting at night (ALAN), urbanized individuals can potentially garner information from conspecific eyes under both daylight and ALAN. We tested this possibility using a visual modeling approach in which we estimated the maximum distance at which individuals could detect conspecific eyes under daylight and high levels of ALAN. We also estimated the minimum light level at which individuals could detect conspecific eyes. Great-tailed grackles (Quiscalus mexicanus) were used as our study species because they are highly social and are unusual among birds in that they regularly gather at nocturnal roosts in areas with high levels of ALAN. This visual modelling approach revealed that grackles can detect conspecific eyes under both daylight and ALAN, regardless of iris coloration. The grackles could detect conspecific eyes at farther distances in daylight compared to ALAN. Our results highlight the potential importance of lighting conditions in shaping social interactions.

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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.
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en Feather coloration and patterning are major signals influencing mate choice within and between species. However, most studies of the role of plumage in mate choice have focused on colorful species with obvious sexual dichromatism. To better understand how achromatic plumage might influence hybridization, we quantified plumage variation between and within two achromatic songbirds that occasionally hybridize, Black-capped (Poecile atricapillus) and Mountain (P. gambeli) chickadees. We collected feathers from 43 live birds and photographed 155 prepared museum specimens to measure overall plumage color and the size of the throat and cheek patches. Using principal component analyses and generalized linear mixed models, we characterized plumage patterns within and between Black-capped and Mountain chickadees from Colorado to examine plumage color variation and differences in throat and cheek patch size. We found that Black-capped Chickadees (1) were less achromatic and had brighter plumage with more color contrast than Mountain Chickadees, (2) had smaller throat and cheek patches than Mountain Chickadees, and (3) were not sexually dimorphic. We also found that male Mountain Chickadee museum specimens had brighter plumage with more ultraviolet reflectance than female museum specimens (i.e., they are sexually dimorphic). However, we did not observe sexual dimorphism in live Mountain Chickadees, potentially because we did not sample the supercilium. In contrast to previous studies, we found that Black-capped Chickadees are not sexually dimorphic, potentially because plumage is not used in mating decisions for populations at lower latitudes. Between Black-capped and Mountain chickadees, differences in plumage color and patch sizes may influence hybridization if female Mountain Chickadees prefer the brighter plumage and greater color contrast of male Black-capped Chickadees. Our results will guide future work exploring the role plumage might play in hybridization between Black-capped and Mountain chickadees by informing plumage manipulation experiments investigating the influence of brighter plumage and color contrast in hybridization. RESUMEN es Variación acromática del plumaje inter- e intra-híbridos en los carboneros Poecile atricapillus y P. gambeli La coloración y patrones de las plumas son señales mayores que influencian la selección de parejas intra- e interespecíficamente. Sin embargo, la mayoría de los estudios del papel del plumaje en la selección de pareja se han enfocado en especies coloridas con un evidente dicromatismo sexual. Para entender mejor cómo el plumaje acromático podría influenciar la hibridación, cuantificamos la variación del plumaje intra- e inter-específica de dos aves canoras que ocasionalmente se hibridan, los carboneros Poecile atricapillus y P. gambeli. Colectamos plumas de 43 aves vivas y fotografiamos 155 especímenes de museo para medir el color total del plumaje y el tamaño de los parches de garganta y mejillas. Usando un análisis de componentes principales y modelos lineales generalizados mixtos, caracterizamos los patrones del plumaje intra- e inter-específicos de estos carboneros de Colorado para examinar la variación y las diferencias en el tamaño de los parches de garganta y mejillas. Encontramos que P. atricapillus (1) fueron menos acromáticos y tuvieron un plumaje más brillante con más contraste de color que P. gambelli, (2) tenían parches de garganta y mejillas más pequeños que los de P. gambelli y (3) no son sexualmente dimórficos. También descubrimos que los especímenes de museo de machos de P. gambelli tenían un plumaje más brillante con mayor reflectancia ultravioleta que los especímenes de museo de hembras (i.e., son sexualmente dimórficos). Sin embargo, no observamos dimorfismo sexual en P. gambelli vivos, potencialmente porque no muestreamos el supercilium. En contraste con estudios previos, encontramos que P. atricapillus no son sexualmente dimórficos, potencialmente porque su plumaje no se usa en decisiones de apareamiento en poblaciones a latitudes más bajas. Entre P. atricapillus y P. gambelli, las diferencias en color del plumaje y los tamaños de parche podrían influenciar la hibridación si las hembras de P. gambelli prefieren el color más brillante y con mayor contraste de color de los machos de P. atricapillus. Nuestros resultados guiarán trabajo futuro para explorar el papel que el plumaje podría jugar en la hibridación entre estos carboneros, informando experimentos de manipulación de plumaje para investigar la influencia del brillo y el contraste de color del plumaje en la hibridación.
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Birds show huge variation in color displays evolved for communication. However, among colored phenotypic traits, eyes remain largely overlooked, with only a few studies suggesting a potential signaling function or a role in mate recognition and crypsis. Iris color is a remarkably striking feature in the wholly cryptic pattern of many owls, and may potentially play a signaling function, a possibility so far neglected. Here, we studied variation and potential signaling of iris yellowness as an indicator of quality in parent-offspring communication and other social contexts in the Little Owl (Athene noctua) and Eurasian Scops-Owl (Otus scops). Yellowness did not differ between the sexes; however, adults of the two species had more intensely yellow irises than owlets. Most of variation in iris yellowness of owlets occurred between rather than within nests and seemed to be linked to parental qualities of Little Owls, but was unrelated to condition among Eurasian Scops-Owl owlets. In adults, however, we found that iris yellowness of females was positively associated with nest success (an index of female fitness) in Little Owls, but not in Eurasian Scops-Owls. This study suggests that iris color variation is unlikely to play a role in parent-offspring communication for these two owl species, but that iris yellowness of female Little Owls may potentially play a signaling role in social contexts, a possibility that should be studied in the future.
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Birds use spectral information for circadian control, magnetic orientation and phototaxis but most importantly for discriminating the colours of important objects such as food items or mates. Their tetrachromatic colour vision is based on four types of single cones expressing four opsin-based visual pigments and fine-tuned by the carotenoid composition in cone oil droplets. Bird colour vision is not as uniform as previously thought, and single visual pigments have been lost in several bird lineages. Diurnal birds have fine colour discrimination and good colour constancy but can generalize over similar though discriminable colours. Bird colour discrimination is ultimately limited by receptor noise but can be impaired in natural conditions, depending on light intensity and background coloration.
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Plumage traits have been studied intensely for more than a century, especially bright and exaggerated plumage. A large body of evidence across a range of avian taxa supports sexual selection as a major evolutionary force acting on plumage colors. The discovery of ultraviolet (UV) coloration in avian plumage resulted in the extension of sexual selection hypotheses to explain the evolution of potential UV plumage traits. However, there have been no comparative evolutionary studies elucidating the origin of UV signals in birds. Here, I used a comparative phylogenetic approach to investigate the evolution of chromatic UV plumage colors in the grackles-and-allies clade of the New World blackbirds (Icteridae). On the basis of reflectance data collected from museum study skins, I have determined that UV plumage signals have evolved multiple times from an ancestral condition that lacked UV plumage signals, with very few unambiguous reversals. Although UV plumage has evolved in both males and females, there have been significantly more evolutionary changes in male UV plumage characters. Concentrated changes tests and correlations of independent contrasts reveal evidence for sexual selection of some male UV plumage characters, as well as an increase in UV plumage coloration for species found in open habitats. These results support the use of objective assessments of avian colors (i.e. spectrophotometry) to properly interpret patterns of plumage evolution generally, and they suggest the need for behavioral studies on the function of chromatic UV signals in several blackbird species. Una Perspectiva Filogenética sobre la Evolución de la Coloración Ultravioleta en los Changos y Chamones (Icteridae)
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Avian ocular disease may be primary or a manifestation of systemic disease. Various infectious and noninfectious diseases have been reported to cause ocular pathology. Thorough physical examination and diagnostic testing are necessary to determine a treatment plan.
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Many animals use vision to detect, discriminate, or recognize important objects such as prey, predators, homes, or mates. These objects may differ in color and brightness—having chromatic and achromatic contrast to the background or to other objects. Visual models are powerful tools to investigate contrast detection, but need to be calibrated by experimental data to provide robust predictions. The most critical parameter of current models—receptor noise—is usually estimated from a small number of behavioral tests on chromatic contrast thresholds, while equivalent tests of achromatic thresholds in a wide range of animals have often been ignored. We suggest that both chromatic and achromatic contrasts in studies of visual ecology should be examined using calibrated model parameters, and we provide a compilation of what is currently known on visual thresholds and corresponding noise estimates. Besides the need for careful parameter estimation, we discuss how the robustness of model predictions depends on assumptions about overall light intensity, background color and brightness, object size, and behavioral context.
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Visual acuity is one of three basic parameters that characterize a visual system. However, few comparative studies of signals, camouflage and ecology in general have considered visual acuity. This is unfortunate, because humans have high acuity, and thus researchers may focus on visual details of animals and habitats that are not actually visible to the relevant species. Here we present AcuityView, a package for use in the software r which uses Fourier methods, measures of a viewer's acuity, viewing distance and the size of an image to modify images. AcuityView renders an image in a way that preserves only the information that an animal with a given visual acuity can detect at a certain distance, thus displaying an image that shows only the visual information available to that viewer. Ultimately, this will allow for a more informed analysis of what aspects of an animal's visual world may be detectable, and thus relevant to their ecology.
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Christopher Kyba, Andrej Mohar and Thomas Posch seek a standard figure for moonlight illuminance.
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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.
Article
1957). This study concerns criteria of age in the Boat-tailed Grackle (Cassidix mexicanus prosopidicola) derived from examination of specimens from central Texas. Special attention is given to criteria by which first-year and adult birds can be distinguished, in order to compare the annual reproductive cycles of these two age groups (Selander and Hauser, MS). The investigation is also designed to serve as groundwork for the author's comparative studies of behavior and phylogeny in the grackles. The present study is based on 328 males and 165 females collected over a 16-month period in 1956 and 1957, within a ten-mile radius of Austin, Travis County, Texas. Specimens were processed as follows: The left testis or ovary was removed and placed in Bouin's fixative in preparation for histologic studies; body weight was recorded (within two hours after death); extent of molt, if any, was recorded in detail for each feather tract and its regions; types and numbers of juvenal feathers retained through the postjuvenal molt by first-year individuals were noted; extent of skull ossification was determined; iris color was recorded; relative amount of body fat was noted; and measurements of wing, tail, bill, tarsus, and middle toe were taken. Approximately 10 per cent of the specimens were prepared as study skins or skeletons and deposited in the Texas Natural History Collection. Age determination of males presents relatively few problems. First-year males are duller and less glossy or iridescent than adult males and generally can be recognized at a glance (fig. 2). The duller color, in combination with a shorter and narrower tail, is generally so conspicuous that first-year birds are recognizable in the field. Care must be exercised in individual cases, however, because some first-year males are nearly as iridescent and dark as adults, particularly after the prenuptial molt, and have adultlike tails. Age determination of females is a much more difficult problem and cannot be accomplished with certainty on the basis of plumage color alone. In worn plumage, color is of little value in age determination. In studying the race C. m. monsoni, Phillips (1950) had only limited success in aging female museum specimens, and he stressed the need in taxonomic studies for females of known age. The need to establish criteria by which first-year and adult females can be identified with confidence and to test the validity of plumage color as an age criterion in males has necessitated a detailed investigation of molt. Characters other than color that were examined for use in determining age are feather shape and degree of wear, retention of juvenal feathers through the postjuvenal molt, iris coloration, degree of skull ossification or double layering, and size. Using a combination of characters, it has been possible to age all specimens collected. Some characters are of value not only in Cassidix but in related genera of icterids as well. MOLTS AND PLUMAGES
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Los caracteres del plumaje, en especial los colores brillantes y los rasgos exagerados, han sido estudiados intensamente durante más de un siglo. Existe un cúmulo amplio de evidencia en distintos taxa de aves que apoya la hipótesis de que la selección sexual es una importante fuerza evolutiva que actúa sobre la coloración del plumaje. El descubrimiento de la coloración ultravioleta (UV) en el plumaje de las aves conllevó a la extensión de la hipótesis de selección sexual para explicar la evolución de los caracteres UV del plumaje. Sin embargo, no existen estudios evolutivos comparativos que hayan elucidado el origen de las señales UV en las aves. En este estudio, empleé un enfoque filogenético comparativo para investigar la evolución de la coloración UV del plumaje en el clado de los changos y chamones, que forma parte de la familia Icteridae. Con base en datos de reflectancia obtenidos a partir de pieles de museo, determiné que las señales UV han evolucionado repetidamente a partir de una condición ancestral que carecía de señales UV, con muy pocas reversiones no ambiguas. Aunque la coloración UV del plumaje ha evolucionado tanto en los machos como en las hembras, han existido significativamente más cambios evolutivos en los caracteres UV de los machos. Pruebas de cambios concentrados y correlaciones de contrastes independientes proveen evidencia de la existencia de selección sexual sobre algunos de los caracteres UV de los machos, y de un incremento en la coloración UV en las especies que habitan ambientes abiertos. Estos resultados apoyan el uso de mediciones objetivas de los colores de las aves (i.e. espectrofotometría) para interpretar los patrones de evolución del plumaje en general, y sugieren la necesidad de estudios de comportamiento que permitan elucidar la función de las señales cromáticas UV en varias especies de ictéridos.
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We report on mortality caused by an evening hailstorm to a night-time roost of Great-tailed Grackles (Quiscalus mexicanus) and European Starlings (Sturnus vulgaris) in Austin, Texas. The hailstorm was of short duration (6 min), and hail stones were not too large (most <20 mm in diameter). Approximately 7% of female grackles, 12% of male grackles, and 26% of starlings died. Greater mortality in male grackles suggests that preferred roost locations were more exposed to hail.
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1. Kirschfeld (1976) suggested that visual acuity is directly proportional to body length across a wide range of animal species. A survey of eye size, visual acuity and body size of birds and mammals that is consistent with Kirschfeld's suggestion is reported. Hypoallometry (scaling factor < 1) for eye size vs body size combines with hyperallometry (scaling factor > 1) for acuity vs eye size to produce roughly linear scaling between acuity and body size. 2. Kirschfeld (1976) also suggested that the distance at which important objects are typically viewed is a linear function of body length. ‘Subjective distance’ (viewing distance/body length) was therefore thought to be independent of body size across species. However, for prey detection by mammalian and avian predators, it is doubtful that subjective visual distances are size independent because prey size and visual acuity both scale by factors > 0·5 with predator body size; hence, detection distance should scale with size by a factor > 1. Scaling analyses also suggest that subjective visual distances for intraspecific social interactions are size dependent. 3. A positive association between body size and viewing distance has implications for the scaling of coat pattern features. In environments with fractal visual backgrounds (in which perceived sizes of background pattern elements do not change as distance from the background changes), larger animal species should have larger coat patches than smaller species if they are adapted to be cryptic at greater viewing distances than smaller species are.
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This study analyzed the occurrence of selected facial expressions, gestures, and postures, in relation to sex and rank of sender and receiver, context, and responses elicited in a large multi-male multi-female group of rhesus macaques (Macaca mulatta) living in captivity. The group was observed for 100 hr during the mating and the birth season. Data were collected with the behavior sampling method. The bared-teeth display and the hindquarter presentation were the most prominent signals in the rhesus submissive and affiliative repertoire. Both signals were primarily displayed in response to aggression and approaches; bared-teeth in response to approaches from the front, presentation in response to approaches from the rear. Lip-smack had a submissive component like baredteeth and presentation but was more likely to be displayed by approaching individuals and followed by affiliation than these behaviors. The distribution of hip-touch and mount was different from that of bared-teeth, presentation, and lip-smack, these behaviors mostly occurring between males, irrespective of their dominance rank. Other infrequent signals and behavioral sequences were limited to specific male-female and mother-infant interactions.
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The energetic expenditure of displaying male sage grouse, Centrocercus urophasianus, was measured for 18 individuals in the field using the doubly labelled water technique. Daily energy expenditure increased significantly with increased display rate, increased time spent on the lek, and decreased ambient temperature. Daily energy expenditure for the most vigorously displaying males was two times higher than for a non-displaying male and four times higher than basal metabolic rate. Estimates of the instantaneous rate of energy expenditure during display ranged from 13·9 to 17·4 times basal metabolic rate. The effort devoted to display differed markedly among males and was correlated with certain other male characteristics. Males that attended leks were in better condition (higher body weight relative to size) than non-attenders, but among lek attenders condition was negatively correlated with increased display effort. Active displayers lost less weight per day and foraged further from the lek than less active males, suggesting that differences in foraging and food intake affect daily energy output. Neither blood parasites nor the potential effects of other diseases as determined by haematocrit levels were associated with display effort.