Experimental support for the makeup hypothesis in nestling tawny owls (Strix aluco)

Body condition can affect coloration of traits used in sexual selection and parent-offspring communication by inducing rapid internal changes in pigment concentration or aggregation, thickness of collagen arrays, or blood flux. The recent "makeup hypothesis” proposes an alternative honesty-reinforcing mechanism, with behaviorally mediated deposition of substances on body surfaces ("cosmetics”) generating covariation between body condition and coloration. In birds, the uropygial gland wax is actively spread on feathers using the bill and changes in its deposition rate may cause rapid changes in bill and plumage coloration. Using tawny owl nestlings, we tested 3 predictions of the makeup hypothesis, namely that 1) quantity of preen wax deposited accounts for variation in bill coloration, 2) an immune stimulation (induced by injection of a lipopolysaccharide [LPS]) impairs uropygial gland wax production, and 3) different intensities of immune stimulations (strong vs. weak stimulations induced by injections of either LPS or phytohemagglutinin [PHA], respectively) and high versus low food availabilities result in different bill colorations. We found that 1) preen wax reduced bill brightness, 2) a challenge with LPS impaired uropygial gland development, and 3) nestlings challenged with LPS had a brighter bill than PHA-injected nestlings, whereas diet manipulation had no significant effect. Altogether, these results suggest that a strong immune challenge may decrease preen wax deposition rate on the bill of nestling birds, at least by impairing gland wax production, which causes a change in bill coloration. Our study therefore highlights that cosmetic colors might signal short-term variation in immunological statu

Function of the uropygial gland in eiders (Somateria mollissima)

International audienceBackground: The uropygial gland is an exocrine gland located above the tail of birds that produces a diverse range of biochemicals. It has been hypothesized to be involved in chemical protection, water-proofing and maintenance of plumage brightness. Although these not necessarily mutually exclusive functions have received some empirical support , there has been little empirical research on the function of water-proofing. Methods: Here we analyzed data for 229 individual eiders (Somateria mollissima) collected by Danish hunters during 2016-2018. Results: The Eider is a sea-duck that spends almost its entire life in sea water emphasizing water-proofing of the plumage. The size of the uropygial gland increased with body mass in males, but not in females, and it increased with age. The size of the uropygial gland decreased during winter. Eiders with small uropygial glands grew their feathers at a fast rate. Eiders with large wing areas had large uropygial glands. Conclusions: These findings are consistent with large uropygial glands playing a role in water-proofing during molt and foraging, but also that uropygial glands may play a role in chemical defense

Métaux traces : réponses écophysiologiques et rôle dans le maintien du polymorphisme de coloration mélanique du plumage chez le pigeon biset

Trace metals, such as lead and zinc are mainly emitted by human activities, explaining their high concentrations in urban areas in comparison with rural environments. During my PhD, I first investigated the ecotoxicological effects of a chronic exposure to lead and/or zinc, two abundant metals in urban areas, in feral pigeons (Columba livia). I stressed deleterious effects of lead, while beneficial effects of zinc on immunity, body mass index maintenance and several parameters of reproduction. Because sensitivity to trace metals differs between individuals, trace metals may exert new selective pressures on urban populations and favour individuals with higher detoxification capacities and that are more tolerant to elevated environmental trace metals concentrations. My work puts ahead the role of melanin in the storage of zinc and lead in the feathers. Moreover, melanin-based plumage colouration seems to modulate the effects of lead and zinc on some of the physiological parameters measured and darker juveniles were more prone to survive than paler ones when exposed to lead. Whatever the underlying mechanism (i.e. the detoxification role of melanin or the pleiotropic effects associated with its synthesis), my results suggest a selective advantage of plumage melanism in environments polluted with trace metals, such as urban areas. This study brings key answers on the ecological impact of urbanization and on the mechanisms explaining melanin-based plumage colouration polymorphism maintenance.Les métaux traces comme le plomb, le zinc sont essentiellement émis par les activités anthropiques et se retrouvent de ce fait à des concentrations beaucoup plus élevées en milieux urbains qu’en milieux ruraux. Durant ma thèse, j’ai tout d’abord testé les effets écotoxicologiques d’une exposition chronique au plomb et/ou au zinc, deux métaux particulièrement abondants en milieu urbain, chez le pigeon biset (Columba livia). J’ai ainsi pu montrer des effets nocifs du plomb, et bénéfiques du zinc sur l’immunité, le maintien de la corpulence et plusieurs paramètres de la reproduction. Du fait de la variabilité des réponses écophysiologiques des individus, les métaux traces sont susceptibles d’exercer de nouvelles pressions de sélection sur les populations urbaines et favoriser les individus capables de se détoxifier ou de tolérer de fortes concentrations en métaux. Au cours de ma thèse, j’ai mis en évidence le rôle de la mélanine dans la fixation du zinc et du plomb au niveau des plumes. Par ailleurs la coloration mélanique du plumage semblent moduler les effets du plomb et du zinc sur certains paramètres physiologiques, et les juvéniles au plumage davantage mélanique survivent mieux dans un environnement pollué en plomb. Quels que soient les mécanismes sous-jacents (i.e. rôle détoxifiant de la mélanine ou effets pléiotropes associés à sa synthèse), mes résultats soulignent l’avantage sélectif potentiel de la mélanisation du plumage dans un environnement pollué en métaux traces, dont notamment le milieu urbain. Cette étude apporte des réponses essentielles sur l’impact écologique de l’urbanisation et les mécanismes permettant le maintien du polymorphisme de coloration mélanique du plumage, et plus largement des phanères

Plumage brightness and uropygial gland secretions in barn swallows

The uropygial gland has been hypothesized to play a role in sexual signaling through a "make-up" function derived from the effects of secretions from the gland on the appearance of the plumage and bare parts of the body. Here we show that plumage brightness of dorsal feathers of individual barn swallows Hirundo rustica was greater in mated than in unmated individuals. In addition, plumage brightness increased with colony size. Furthermore, plumage brightness was positively correlated with the amount of wax in the uropygial gland, negatively correlated with time of sampling of uropygial wax (perhaps because more wax is present early in the morning after an entire night of wax production without any preening), and negatively correlated with the number of chewing lice that degrade the plumage. Experimentally preventing barn swallows from access to the uropygial gland reduced plumage brightness, showing a causal link between secretions from the uropygial gland and plumage brightness. These findings provide evidence consistent with a role of uropygial secretions in signaling plumage brightness

Sexual selection and blue tit (Parus caeruleus) crown coloration

Conspicuous, sexually dimorphic plumage in birds is most likely a consequence of sexual selection favouring more ornamented males at obtaining a territory and/or a mate. Recent comparative analyses suggest that, among socially monogamous species, extra-pair paternity has also contributed to the elaboration of male ornaments. If females prefer more ornamented males as social or extra-pair mates this could translate into strong directional selection for ornament elaboration, since these males might sire more offspring in their own brood (within-pair success) or in broods of other males (extra-pair success). In this thesis I study the expression of the UV/blue crown coloration in the blue tit (Parus caeruleus) and investigate whether this trait could be selected through increased male within- or extra-pair success. Blue tits are socially monogamous passerines with relatively high levels of extra-pair paternity, and males in this species display more ultraviolet(UV)/blue reflectant crown feathers than females. Based on three years of data I found that crown coloration could be a cue used by females to assess male age since blue tits became more UV-ornamented as they aged. Crown coloration, however, did not correlate with survival to the next breeding season, suggesting that more UV-ornamented males are not necessarily of higher quality. While crown UV-ornamentation increased between years, it declined in the course of a year due to feather wear and dirt accumulation and this could affect female perception of male attractiveness. However, although the decline in UV ornamentation between winter and spring was large, it had no effect on male reproductive success, and winter and spring colour were still positively correlated. Using genetic paternity analysis I could show that more UV-ornamented males do not benefit through increased within-pair or extra-pair success. On the contrary, less UV-ornamented, adult males sired most of the extra-pair offspring. Hence the most successful males of the population were adult males that resembled juveniles in their crown colour. Accordingly, females seem to recognise less UV-ornamented males as highly successful, since they biased brood sex ratio towards male offspring if paired to these males. The causality of these patterns was tested in a colour manipulation experiment, where I treated males to become more (UV+) or less (UV-) ornamented within the natural range of variation. Against expectations UV(+) males sired significantly more extra-pair offspring than UV(-) males while the proportion of within-pair offspring was unaffected by the manipulation. Brood sex ratios did not differ between treatments but depended on male colour before manipulation. While these results do suggest that crown colour plays a role in paternity and brood sex allocation, they do not provide experimental support for the observed correlational patterns. I discuss the discrepancy between observational and experimental data, emphasising potential problems with the experimental manipulation of structural plumage colour. Finally, given that more UV-ornamented males did not sire more offspring, I explore the possibility that they would benefit by pairing with high quality females. High quality females in other species are often more ornamented, and birds of high quality pair assortatively based on ornament expression. This was not the case in this blue tit population, since female colour did not appear to indicate relevant female qualities (fecundity, seasonal reproductive success) and blue tits did not mate assortatively by crown colour in any of the three study years. To conclude, selection seems to favour older, less UV-ornamented males in this population. Whether this is due to female preference is unclear. Alternatively I hypothesise that being less ornamented may enable males searching for extra pair copulations to intrude into other territories without eliciting aggression by territory owners, perhaps by mimicking juveniles. Detailed behavioural observations in the wild coupled with choice chamber experiments in captivity are necessary to test this idea

The Abyssinian Art of Louis Agassiz Fuertes in the Field Museum

This book documents the paintings and drawings executed by Louis Agassiz Fuertes during the Field Museum of Natural History’s seven-month expedition to Ethiopia (Abyssinia) in 1926–27. During that time Fuertes completed 70 field watercolors that illustrate 55 species of birds and four species of mammals. He also executed 34 pencil drawings, which illustrate 13 species of mammals and 11 species of birds, plus numerous miscellaneous sketches and small watercolors. This book identifies and describes the biology of all 69 species of birds and mammals illustrated by Fuertes and includes 32 color reproductions of Fuertes’s watercolors that were published as a limited-edition album in 1930 by the Field Museum. The 60,000-word text provides brief summaries of all these species’ ecology, behavior, and reproductive biology as well as information about their current populations and conservation status. A review of Fuertes’s life, his influence on modern bird and wildlife art, and his participation in and artistic contributions to the Field Museum’s Abyssinian Expedition is also included, as well as more than 250 bibliographic citations.https://digitalcommons.unl.edu/zeabook/1083/thumbnail.jp