Nonideal nest box selection by tree swallows breeding in farmlands: evidence for an ecological trap?

Animals are expected to select a breeding habitat using cues that should
reflect, directly or not, the fitness outcome of the different habitat
options. However, human-induced environmental changes can alter the
relationships between habitat characteristics and their fitness
consequences, leading to maladaptive habitat choices. The most severe case
of such nonideal habitat selection is the ecological trap, which occurs
when individuals prefer to settle in poor-quality habitats while better
ones are available. Here we studied the adaptiveness of nest box selection
in a tree swallow (Tachycineta bicolor) population breeding over a 10-year
period in a network of 400 nest boxes distributed along a gradient of
agricultural intensification in southern Québec, Canada. We first
examined the effects of multiple environmental and social habitat
characteristics on nest box preference to identify potential settlement
cues. We then assessed the links between those cues and habitat quality as
defined by the reproductive performance of individuals that settled early
or late in nest boxes. We found that tree swallows preferred nesting in
open habitats with high cover of perennial forage crops, high spring
insect biomass, and high density of house sparrows (Passer domesticus),
their main competitors for nest sites. They also preferred nesting where
the density of breeders and their mean number of fledglings during the
previous year were high. However, we detected mismatches between
preference and habitat quality for several environmental variables. The
density of competitors and conspecific social information showed severe
mismatches, as their relationships to preference and breeding success went
in opposite direction under certain circumstances. Spring food
availability and agricultural landscape context, while related to
preferences, were not related to breeding success. Overall, our study
emphasizes the complexity of habitat selection behavior and provides
evidence that multiple mechanisms may potentially lead to an ecological
trap in farmlands.