Ecological Trap Effects in Migratory European Pied Flycatchers (Ficedula hypoleuca) Nesting in Pest Outbreak-Affected Forests

When selecting a habitat, it is optimal for organisms to choose one that maximizes reproductive success through access to high-quality resources, particularly in species that engage in parental care. However, organisms may inadvertently select a habitat for breeding that would initially appear preferential and undamaged, but may, in reality, be detrimental to parent and/or offspring fitness. In this study, we tested whether migratory European Pied Flycatchers (Ficedula hypoleuca) nesting in forest patches affected by outbreaks of the great web-spinning sawfly (Acantholyda posticalis) experienced fitness reductions indicative of an ecological trap, compared to those nesting in unaffected forest patches. After installing nest boxes to attract breeding pairs and potentially combat the outbreak, we found that Flycatchers inhabiting areas with sawfly outbreaks had similar clutch sizes to pairs breeding in unaffected forest patches. Contrarily, the fledgling number and body condition were significantly lower for those nesting in the damaged forests. In providing nest boxes for migrating Flycatcher pairs in forest patches that were subsequently impacted by a pest insect outbreak, an ecological trap arose for those pairs choosing to nest in what appeared to be an unaffected forest at first. Given the inability of breeding pairs to distinguish habitat quality on initial inspection, we suggest that nest boxes be used with caution in areas with unfavorable habitat conditions when attracting migratory birds, given the trends of their declining global numbers.