Data from: The evolution of using shed snake skin in bird nests

Many species of birds use shed snake skin in nest construction, but this
behavior remains poorly understood. Ecological context is likely key for
understanding how this unusual, but widespread, behavior evolved. We use
comparative and experimental approaches to suggest that the evolution of
this behavior is mediated by nest morphology and predator communities.
First, we reviewed the literature and found that 78 species from 22
families have been reported to use shed snake skin in nest construction.
All but one of these species are passerines and, using comparative
analyses, we show that this behavior is disproportionately observed in
cavity-nesting species. Second, we examined a subsample of North American
species, all of which are reported to use snake skin in nest construction,
to see if the proportion of nests with snake skin differs between cavity
and open cup-nesting species. This analysis suggested that the proportion
of nests with snake skin is roughly 6.5 times higher in cavity than in
open cup-nesting species. Finally, we used a series of experiments and
comparisons to test four hypotheses whereby snake skin could award fitness
benefits (nest predation, nest microbiotas, nest ectoparasites, social
signaling) and found support for the predation hypothesis. Snake skin
reduced nest predation in cavity, but not open cup, nests. These unequal
fitness benefits highlight different ecological conditions between nest
morphologies and likely explains why, across species, cavity-nesting birds
show this behavior more frequently compared to open cup-nesting birds.