Disentangling relationships between physiology, morphology, diet, and gut microbial diversity in American Kestrel nestlings

Gut microbiota are increasingly recognized as important drivers of host health and fitness across vertebrate taxa. Given that gut microbial composition is directly influenced by the environment, gut microbiota may also serve as an eco-physiological mechanism connecting host ecology, such as diet, and physiology. Although gut microbiota have been well-studied in mammalian systems, little is known about how gut microbial diversity and composition impact morphological and physiological development in wild birds. Here, we characterized both diet and gut microbial diversity of free-living American kestrel (Falco sparverius) nestlings throughout development to test whether gut microbial diversity predicts host morphological and physiological traits in either contemporary or time-lagged manners. Gut microbial alpha diversity on day 21 of nestling development was positively correlated with diet alpha diversity representative of the majority of nestling development (days 5–20). Gut microbial alp..., Sample Collection
We monitored American kestrel (Falco sparverius) nest-boxes in Berks, Lehigh, and Schuylkill Counties, Pennsylvania, USA beginning in early May 2018 and 2019 to document occupancy, egg-laying date, and hatching as described in Cornell et al. (2021). In 2018, we sampled 12 nestlings from 4 nests, and in 2019 we sampled 32 nestlings from 10 nests (n = 44 nestlings total). On days 7, 14, and 21 after hatching (hatch day = day 0), we removed nestlings from the nest and collected morphometrics, blood samples, and fecal samples between 8:00 and 12:00 hours (following university IACUC and US Fish and Wildlife Service banding permits). Birds were sexed on day 21 from coloration of primary feathers: blue for males and brown for females (Smallwood and Bird 2020). We measured mass to the nearest 0.01 g using a digital scale. We banded nestlings with uniquely colored temporary leg bands (Darvic Wraparound 1FB, 5.5 mm, Avinet) on day 7 for identification within nests and banded wit..., We have included scripts for QIIME2 (version 2021.11) and R (version 4.2.1). See READMe for more information.
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