Gray plumage color is more cryptic than brown in snowy landscapes in a resident color polymorphic bird

Camouflage may promote fitness of given phenotypes in different environments. The tawny owl (Strix aluco) is a color polymorphic species with a gray and brown morph resident in the Western Palearctic. A strong selection pressure against the brown morph during snowy and cold winters has been documented earlier, but the selection mechanisms remain unresolved. Here, we hypothesize that selection favors the gray morph because it is better camouflaged against predators and mobbers in snowy conditions compared to the brown one. We conducted an online citizen science experiment where volunteers were asked to locate a gray or a brown tawny owl specimen from pictures taken in snowy and snowless landscapes. Our results show that the gray morph in snowy landscapes is the hardest to detect whereas the brown morph in snowy landscapes is the easiest to detect. With an avian vision model, we show that, similar to human perceivers, the brown morph is more conspicuous than the gray against coniferous tree trunks for a mobbing passerine. We suggest that with better camouflage, the gray morph may avoid mobbers and predators more efficiently than the brown morph and thus survive better in snowy environments. As winters are getting milder and shorter in the species range, the selection periods against brown coloration may eventually disappear or shift poleward.Peer reviewe

Separating the effects of predation risk and interrupted foraging upon mass changes in the blue tit Parus caeruleus

The optimal amount of reserves that a small bird should carry depends upon a number of factors, including the availability of food and environmental predation risk levels. Theory predicts that, if predation risk increases, then a bird should maintain a lower level of reserves. Previous experiments have given mixed results: some have shown reduced reserves and some, increased reserves. However, the birds in these studies may have been interpreting a staged predation event as a period when they were unable to feed rather than a change in predation risk: theory predicts that, if the food supply within the environment is variable, then reserves should be increased. In the present study, we presented blue tits (Parus caeruleus) with a potential predator and compared this response (which could have been potentially confounded by perceived interruption e¡ects) with a response to an actual interruption in the environment during both long and short daytime lengths. During long (but not short) days, the birds responded in line with theoretical predictions by increasing their reserves in response to interruption and reducing them in response to predation. These results are examined in the light of other experimental manipulations and we discuss how well experimental tests have tested the predictions made by theoretical models

Human preferences for sexually dimorphic faces may be evolutionarily novel

This article has been made available through the Brunel Open Access Publishing Fund.A large literature proposes that preferences for exaggerated sex typicality in human faces (masculinity/femininity) reflect a long evolutionary history of sexual and social selection. This proposal implies that dimorphism was important to judgments of attractiveness and personality in ancestral environments. It is difficult to evaluate, however, because most available data come from largescale, industrialized, urban populations. Here, we report the results for 12 populations with very diverse levels of economic development. Surprisingly, preferences for exaggerated sex-specific traits are only found in the novel, highly developed environments. Similarly, perceptions that masculine males look aggressive increase strongly with development, specifically, urbanization. These data challenge the hypothesis that facial dimorphism was an important ancestral signal of heritable mate value. One possibility is that highly developed environments provide novel opportunities to discern relationships between facial traits and behavior by exposing individuals to large numbers of unfamiliar faces, revealing patterns too subtle to detect with smaller samples

An effect size statistical framework for investigating sexual dimorphism in non-avian dinosaurs and other extinct taxa

Despite reports of sexual dimorphism in extinct taxa, such claims in non-avian dinosaurs have been underrepresented recently (~the last decade) and often criticized. Since dimorphism is widespread in sexually reproducing organisms today, underrepresentation might suggest either methodological shortcomings or that this diverse group exhibited highly unusual reproductive biology. Univariate significance testing, especially for bimodality, is ineffective and prone to false negatives. Species recognition and mutual sexual selection hypotheses, therefore, may not be required to explain supposed absence of sexual dimorphism across the grade, likely a type II error. Instead, multiple lines of evidence support sexual selection and variation of structures consistent with secondary sexual characteristics, strongly suggesting sexual dimorphism in non-avian dinosaurs. We propose a framework for studying sexual dimorphism in fossils, focusing on likely secondarily sexual traits and testing against all alternate hypotheses for variation in them using multiple lines of evidence. We use effect size statistics appropriate for low sample sizes, rather than significance testing, to analyze potential divergence of growth curves in traits and constrain estimates for dimorphism magnitude. In many cases, estimates of sexual variation can be reasonably accurate, and further developments in methods to improve sex assignments and account for intrasexual variation (e.g., mixture modelling) will improve accuracy. It is better to compare estimates for the magnitude of and support for dimorphism between datasets than to dichotomously reject or fail to reject monomorphism in a single species, enabling the study of sexual selection across phylogenies and time. We defend our approach with simulated and empirical data, including dinosaur data, showing that even simple approaches can yield fairly accurate estimates of sexual variation in many cases, allowing for comparison of species with high and low support for sexual variation.Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: PLR 1341645 and FRES 192588

X-ray photoemission studies of rare earth hard magnets

From 19th conference on magnetism and magnetic materials; Boston, Massachusetts, USA (13 Nov 1973). An attempt was made to probe the electronic properties of the RCo/sub 5/ compounds by x-ray photoelectron spectroscopy studies of SmCo/sub 5/ and PrCo/sub 5/ and to relate the results to the properties o f the pure metals and to the picture developed to describe the magnetism of the compounds. Results indicate a valence band structure similar to that of Co metal; there is the suggestion that if there is charge flow it is off the rare-earth sites; there appears to be significant change in the 4f spectra from that of the pure rareearth metals; and there is a suggestion of f-- d hybridization. (auth