Response to food restriction, but not social information use, varies seasonally in captive cardueline finches.

For songbirds, temperate winters can impose severe conditions on songbirds that threaten survival, including shorter days and often lower temperature and food availability. One well-studied mechanism by which songbirds cope with such conditions is seasonal acclimatization of thermal metabolic traits, with strong evidence for both preparative and responsive changes in thermogenic capacity (i.e., the ability to generate heat) to low winter temperature. However, a bird's ability to cope with seasonal extremes or unpredictable events is likely dependent on a combination of behavioral and physiological traits that function to maintain allostatic balance. The ability to cope with reduced food availability may be an important component of organismal response to temperate winters in songbirds. Here we compare responses to experimentally reduced food availability at different times of year in captive red crossbills (Loxia curvirostra) and pine siskins (Spinus pinus) - two species that cope with variable food resources and live in cold places - to investigate seasonal changes in the organismal response to food availability. Further, red crossbills are known to use social information to improve response to reduced food availability, so we also examine whether use of social information in this context varies seasonally in this species. We find that pine siskins and red crossbills lose less body mass during time-restricted feedings in late winter compared to summer, and that red crossbills further benefit from social information gathered from observing other food restricted red crossbills in both seasons. Observed changes in body mass were only partially explained by seasonal differences in food intake. Our results demonstrate seasonal acclimation to food stress and social information use across seasons in a controlled captive environment and highlight the importance of considering diverse physiological systems (e.g., thermogenic, metabolic, digestive, etc) to understand organismal responses to environmental challenges.

Tales of testosterone: Advancing our understanding of environmental endocrinology through studies of neotropical birds.

Studies of birds have greatly advanced our understanding of how testosterone modulates complex phenotypes, specifically its role in mediating male reproductive and associated behaviors. Yet most of the foundational studies have been limited to northern latitude breeding species despite the fact that they represent only a small fraction of worldwide avian diversity. In contrast, phylogenetic, life-history, and mating system diversity all reach their apex in neotropical avifauna and yet these birds, along with more southern latitude species, remain very poorly understood from an endocrine perspective. Despite the relatively limited previous work on taxa breeding in Central and South America, empirical findings have had a disproportionately large impact on our understanding of testosterone's role in everything from geographic variation to behavioral roles and neuroplasticity. Here, we synthesize how studies of neotropical breeding avifauna have advanced our understanding of how testosterone's actions can and are associated with the broad patterns of phenotypic diversity that we see in birds. In addition, we outline how these studies can be used individually or in a comparative context to address fundamental questions about the environmental endocrinology of testosterone and to understand the diversity of roles that testosterone plays in mediating behavioral variation, reproductive strategies, and associated life-history trade-offs.