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    Hummingbirds, a highly diverse avian family, are specialized vertebrate pollinators that feed upon carbohydrate-rich nectar to fuel their fast metabolism while consuming invertebrates to obtain protein. Previous work has found that morphologically diverse hummingbird communities exhibit higher diet specialization on floral resources than morphologically similar hummingbird communities. Due to the difficulties of studying avian diets, we have little understanding whether hummingbirds show similar patterns with their invertebrate prey. Here, we use DNA metabarcoding to analyze floral and invertebrate diets of 3 species of sympatric North American hummingbirds. We collected fecal samples from 89 Anna’s (Calypte anna), 39 Black-chinned (Archilochus alexandri), and 29 Calliope (Selasphorus calliope) hummingbirds in urban and rural localities as well as across an elevational gradient from sea level to 2,500 meters above sea level in California, USA. We found hummingbirds showed high dietary overlap in both invertebrate and plant resources, with few invertebrate and plant families common to most individuals and many families found in only a few individuals. Chironomidae was the most common invertebrate family across all species, and Rosaceae and Orobanchaceae were the most common plant families. Anna’s Hummingbirds had significantly higher invertebrate diet diversity than Black-chinned Hummingbirds when found at the same sites,more »but we found no difference in plant diet diversity among any of the 3 species. Hummingbirds in urban sites had higher plant diet diversity than in rural sites, but we found no effect of elevation on dietary richness. Our study shows how DNA metabarcoding can be used to non-invasively investigate previously unknown life-histories of well-studied birds, lending insight to community structure, function, and evolution.

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  2. Abstract

    Torpor, or a regulated drop in body temperature and metabolic rate, allows animals to inhabit energetically costly environments, but among torpor‐using species, we have a poor understanding of how plasticity in torpor use relates to the experienced environment.

    To better understand the ecology of daily torpor, we completed the largest study to date on the intraspecific variation of daily torpor use in hummingbirds by exposing 149 individuals of two hummingbird species to ambient or experimentally cooled temperatures in a field setting.

    The smaller species, a latitudinal migrant, used daily torpor frequently under ambient conditions. The larger species, an elevational migrant, also used daily torpor regularly, but further increased the frequency of daily torpor use when experiencing colder temperatures and prior to migration—indicating a facultative adaptation.

    To place our results within a broader phylogenetic context, we combined our experimental results with a meta‐analysis, including 31 species and all major hummingbird clades, and found a broad taxonomic pattern in which smaller hummingbirds are more likely to use daily torpor than their larger counterparts. Smaller hummingbirds may be physiologically constrained, requiring nearly obligate daily torpor use, while larger hummingbirds are physiologically more flexible and can facultatively respond to changing environmental conditions.

    Our results reveal how physiologicalmore »traits, such as the frequency and depth of daily torpor, can provide a mechanism to understand how hummingbird species have established and persisted across broad environmental gradients.

    A freePlain Language Summarycan be found within the Supporting Information of this article.

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  3. Abstract

    While there is huge promise in monitoring physiological parameters in free‐living organisms, we also find high amounts of variability over time and space. This variation requires us to capitalize on long‐term physiological monitoring to adequately address questions of population health, conservation status, or evolutionary trends as long‐term sampling can examine ecoimmunological and endocrine interactions in wild populations while accounting for the variation that often makes ecophysiological field studies difficult to compare. In this study, we tested how immune efficacy and endocrinology interact while accounting for ecological context and environmental conditions in two snake species. Specifically, we measured bacterial killing ability, steroid hormones, and morphological characteristics in multiple populations of the Western Terrestrial Gartersnake (Thamnophis elegans)and Common Gartersnake (T. sirtalis)for multiple seasons over 6 years. Leveraging this long‐term dataset, we tested how a broad immune measure and endocrine endpoints interact while accounting for individual traits, sampling date, and environmental conditions. Across both species, we found bacterial killing ability to be directly related to corticosterone (CORT) and temperature and greater overall in the spring compared to the fall. We found CORT and testosterone yielded relationships with individual sex, sampling temperature, and time of year. Wild populations can exhibit high amounts of variationmore »in commonly collected physiological endpoints, highlighting the complexity and difficulty inherent in interpreting single endpoints without taking ecological and environmental conditions into account. Our study emphasizes the importance of reporting the environmental conditions under which the sampling occurred to allow for better contextualization and comparison between studies.

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