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.