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Physiological preparations for migration generally reflect migratory strategy. Migrant birds fuel long-distance flight primarily with lipids, but carrying excess fuel is costly; thus, the amount of fat deposited prior to departure often reflects the anticipated flight duration or distance between refueling bouts. Seasonal pre-migratory deposition of fat is well documented in regular seasonal migrants, but is less described for more facultative species. We analyze fat deposits of free-living birds across several taxa of facultative migrants in the songbird subfamily Carduelinae, including house finches (Haemorhous mexicanus), American goldfinches (Spinus tristis), pine siskins (Spinus pinus) and four different North American ecotypes of red crossbills (Loxia curvirostra), to evaluate seasonal fat deposition during facultative migratory periods. Our data suggest that the extent of seasonal fat deposits corresponds with migratory tendency in these facultative taxa. Specifically, nomadic red crossbills with a seasonally predictable annual movement demonstrated relatively large seasonal fat deposits coincident with the migratory periods. In contrast, pine siskins, thought to be more variable in timing and initiation of nomadic movements, had smaller peaks in fat deposits during the migratory season, and the partial migrant American goldfinch and the resident house finch showed no peaks coincident with migratory periods. Within the red crossbills, those ecotypes that are closely associated with pine habitats showed larger peaks in fat deposits coincident with autumn migratory periods and had higher wing loading, whereas those ecotypes associated with spruces, Douglas-fir and hemlocks showed larger peaks coincident with spring migratory periods and lower wing loading. We conclude that population averages of fat deposits do reflect facultative migration strategies in these species, as well as the winter thermogenic challenges at the study locations. A difference in seasonal fattening and wing loading among red crossbill ecotypes is consistent with the possibility that they differ in their migratory biology, and we discuss these differences in light of crossbill reproductive schedules and phenologies of different conifer species.

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Climate change is expected to increase the prevalence and severity of extreme weather events like drought. For many opportunistically breeding tropical bird species, precipitation serves as a primary cue for onset of breeding, and sustained drought can have major impacts on reproductive fitness. The physiological effects of drought are poorly understood, but understanding physiological responses can help resolve the mechanisms underlying effects of drought on population demography. We used physiological data collected on a year-round breeding New Guinea endemic passerine, the White-shouldered Fairywren (Malurus alboscapulatus), during years with persistent rainfall and during the 2015-2016 El Niño drought event to assess patterns of breeding readiness, body condition, and molt. Many males lost their cloacal protuberances, a sperm storage organ they typically maintain year-round, during the drought period. Body molt, which also occurs year-round in this species, was higher in males during the drought period. Using a sliding-window statistical model approach, we identified a critical precipitation window of 0-40 days prior to capture for cloacal protuberance volume and a window of 8-53 days for molt, with lower precipitation associated with smaller cloacal protuberances and greater molt. Plasma androgens were predictive of variation in male cloacal protuberance volume and molt, thus potentially mediating transitions between life-history stages in response to environmental conditions. Female molt, androgens, and male mass varied with photoperiod, with longer but decreasing day lengths characteristic of the austral summer associated with increasing molt and decreasing androgens. Collectively, our results indicate the potential for photoperiod to cue some life-history stages, whereas reduced rainfall impacts male but apparently not female reproductive physiology and readiness to breed. Improving our understanding of environmental regulation of life-history transitions in tropical taxa is essential for identifying which taxa are most at risk under a changing climate. La sécheresse perturbe la préparation à la nidification tout au long de l'année chez un passereau tropicalRÉSUMÉ. On prévoit que les changements climatiques augmenteront la prévalence et la gravité des phénomènes météorologiques extrêmes tels que la sécheresse. Pour de nombreuses espèces d'oiseaux tropicaux qui nichent de façon opportuniste, les précipitations sont le principal indice du début de la nidification, et une sécheresse prolongée peut avoir des répercussions importantes sur la capacité de reproduction. Les effets physiologiques de la sécheresse sont mal connus, mais la compréhension des réponses physiologiques peut aider à résoudre les mécanismes sous-jacents aux effets de la sécheresse sur la démographie des populations. Nous avons utilisé les données physiologiques recueillies chez un passereau endémique de Nouvelle-Guinée se reproduisant toute l'année, le Mérion à épaulettes (Malurus alboscapulatus), au cours d'années avec des précipitations ...

Historic bias toward study of male sex hormones and sexual signals currently constrains our perspective of hormone-behavior-phenotype relationships. Resolving how ornamented female phenotypes evolve is particularly important for understanding the diversity of social signals across taxa. Studies of both males and females in taxa with variable female phenotypes are needed to establish whether sexes share mechanisms underlying expression of signaling phenotypes and behavior. White-shouldered Fairywren (Malurus alboscapulatus) subspecies vary in female ornamentation, baseline circulating androgens, and response to territorial intrusion. The moretoni ornamented female subspecies show higher female, but lower male androgens, and a stronger pair territorial response relative to pairs from the lorentzi unornamented female subspecies. Here we address whether subspecific differences in female ornamentation, baseline androgens, and pair territoriality are associated with ability to elevate androgens following gonadotropin releasing hormone (GnRH) challenge and in response to simulated territorial intrusion. We find that subspecies do not differ in their capacity to circulate androgens in either sex following GnRH or territorial intrusion challenges. Whereas pre-GnRH androgens were somewhat predictive of degree of response to territorial intrusions, higher androgens were associated with lower territorial aggression. Post-GnRH androgens were not predictive of response to simulated intruders, nor did females sampled during intrusion elevate androgens relative to flushed controls, suggesting that increased androgens are not necessary for the expression of territorial defense behaviors. Collectively, our results suggest that capacity to produce and circulate androgens does not underlie subspecific patterns of female ornamentation, territoriality, and baseline androgens.