Influence of habitat and climate on nest-site selection, reproductive success and fledgling health in cavity-nesting songbirds in California’s Central Valley

Jason Riggio, Andrew Engilis Jr., Hanika Cook, Evelien De Greef, Daniel Karp and Melanie L. Truan, Wildlife, Fish, and Conservation Biology, University of California, Davis, CA

Background/Question/Methods
Cavity-nesting songbirds provide an ideal model for exploring the influences of habitat and climate on reproductive success as they can be monitored over many nesting seasons at known sites in nest boxes. We tested four hypotheses relating habitat and climate to nest-site selection, reproductive success and fledgling health in four species of cavity-nesting songbirds (Ash-throated Flycatcher, House Wren, Tree Swallow, and Western Bluebird). Using a long-term dataset derived from nest boxes in California’s Central Valley (2004-2020), we built generalized linear mixed models to examine the effects of four habitat and three climatic variables on nest-site selection, reproductive success and fledgling health.
Results/Conclusions
Species-specific habitat characteristics predicted nest-site selection, and generally the same variables were positively correlated with reproductive success and fledgling health. Over the course of the study, average temperature during the nesting period increased while water year precipitation decreased. Conversely, precipitation during the nesting period increased. House Wren, Tree Swallow and Western Bluebird fledgling health was negatively correlated with temperature during the nesting period. Water year precipitation was generally positively associated with reproductive success and fledgling health across species. However, precipitation during the nesting period had differential effects for species. Ash-throated Flycatcher and House Wren reproductive success and fledgling health was positively correlated with precipitation during the nesting period, while Tree Swallow and Western Bluebird reproductive success and fledgling health was negatively correlated with nesting precipitation. Our findings suggest that nest-site selection in cavity-nesting songbirds is species-specific and does not result in ecological traps in our study system. However, increased temperature and decreased precipitation over time are resulting in lower reproductive success and fledgling health for all four species of secondary cavity-nesting songbirds.