Nonideal nest box selection by tree swallows breeding in farmlands:
evidence for an ecological trap?
Abstract
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
relationship between habitat characteristics and their fitness
consequences, leading to a maladaptive habitat choice. 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, 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. Additionally, 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.