Maladaptive habitat selection of a migratory bird in a human-modified landscape : from patterns to mechanisms

(eng) Habitat selection is an individual, behavioural, process during which organisms decide where to live and this decision-making ultimately affects their fitness. Organisms often exhibit preference for habitats that provide rewarding fitness consequences, but this adaptive link between habitat preference and habitat quality might become uncoupled in human-modified environments. Such ecological trapping has received both theoretical and empirical evidence, but the mechanisms leading to this form of maladaptive behaviour remain poorly understood. This thesis focuses on the habitat selection of a migratory bird, the Red-backed shrike (Lanius collurio), breeding in mixed farmland-forest landscapes of southern Belgium. Agricultural activities in farmland and harvesting practices in plantation forests provide structurally different open habitats for shrikes and other open-habitat wildlife. This offers the opportunity to test whether habitat selection is adaptive or if there is evidence for an ecological trap in this study species. A three-year dataset was collected to document habitat preference and habitat quality for the shrikes. A series of key environmental conditions and resources for the shrikes were sampled and compared between both habitat types to examine the mechanisms of habitat selection. Results indicate a preference for open areas in forest over farmland: the forest habitat was found to be valued as a territorial resource to a higher level by the shrikes and, on average, selected before farmland during the habitat selection phase. However, breeding shrikes showed lower reproductive performance in forest than in farmland. This ecological trapping pattern could be partly explained by two different functional components of habitat quality: predation rates and food resources. First, shrikes preferred to settle in the forest habitat with a lower amount of nest predators (i.e. corvids), but where nest predation rate was higher compared to farmland. Among the different factors that were tested to explain this pattern, the limited nest concealment in forest compared to farmland was found to be the best candidate. Second, food limitation offered an additional explanation for the mismatch between habitat preference and quality. Shrikes were shown to be unable to correctly evaluate and deal with the habitat quality in terms of food availability in the breeding sites. This study indicates that open areas in plantation forests may be a less favourable habitat for farmland birds in contrast to what has been assumed previously in the literature. Beyond this applied contribution, this thesis also contributed to the conceptual development of the ecological trapping framework as it draw attention to the importance of food in addition to nest predation as a part of the functional mechanisms underlying this form of maladaptive habitat selection in the wild.