Abstract
Animals with dependent and vulnerable young need to decide where to
raise their offspring to minimize ill effects of weather, competition,
parasitism, and predation. These decisions have critical fitness
consequences through impacting the survival of both adults and
juveniles. Birds routinely place their nest in specific sites, allowing
species to be broadly classified based on nest location (e.g., ground-
or tree-nesting). However, from 2018–2020 we observed 24 American robin
(Turdus migratorius ) nests placed not on their species-typical
arboreal substrates or human-made structures but on the ground at a
predator-rich commercial arbor in Illinois, U.S.A. This behavior does
not appear to be in response to competition and did not affect nest
daily survival rate but was restricted to the early half of the breeding
season. We hypothesize that ground-nesting may be an adaptive response
to avoid exposure and colder temperatures at sites above the ground
early in the breeding season or a non-adaptive consequence of latent
robin nest-placement flexibility.
Keywords: microclimate, nest placement, predation, temperature