Ph.D. Thesis Defense: Ms. Barbara Frei: Roles of maladaptive and evolutionary traps in the decline of a threatened woodpecker
pre-defense will be at 1:45 (room MS2-022A)
The Red-headed Woodpecker (Melanerpes erythrocephalus) is a widespread, once common but increasingly rare North American bird species. Consistent long-term population declines have resulted in the species’ threatened status in Canada and several states in the United States. Throughout most of its range, Red-headed Woodpeckers occupy habitats that have been heavily influenced by human presence and activities. Yet, there is little research quantifying the potential drivers of the species’ population decline, which constrains conservation or policy action. The overall objective of this research is to determine why the Red-headed Woodpecker, a once common, widespread species with apparently a high flexibility in habitat use is undergoing such large population declines. I hypothesize that rapid anthropogenic changes and ecological novelties are causing Red-headed Woodpecker fitness and its behavioural choices to have become disjointed. The specific objectives include: (1) to determine if Red-headed Woodpecker habitat use is adaptive or maladaptive, (2) to determine the influence of a non-native interference competitor, the European Starling (Sturnus vulgaris), on Red-headed Woodpecker breeding success, and (3) to compare the efficacy of global and local models of the relationships between Red-headed Woodpeckers and two possible competitor species over space and time, and explore local variations of these relationships. To test my hypothesis, I investigated Red-headed Woodpecker multi-scale habitat use and associations, and nest survival near the northern edge of the species range in southern Ontario, where populations are rapidly declining. In addition, I modelled interspecies abundance relationships across southern Canada and east-central United States using 45 years of survey data from the Breeding Bird Survey (BBS) for Red-headed Woodpeckers, European Starlings, and Red-bellied Woodpeckers (M. carolinus).
Field-based results demonstrated that Red-headed Woodpeckers exhibit maladaptive habitat use at multiple scales, suggesting the potential for an ecological trap for the species. Specifically habitat characteristics that promoted feeding potential such as canopy openness and greater limb length were consistently associated with Red-headed Woodpecker occupancy from nest tree to woodlot scales, despite correlations with lower reproductive success. Further investigation into Red-headed Woodpecker nest survival by modelling a suite of abiotic, biotic, temporal, and habitat-based drivers showed that European Starling abundance near active woodpecker nest sites was the strongest factors influencing woodpecker nest survival. Logistic-exposure nest success assuming constant survival dropped significantly from 68% to 13% when starling abundance was considered. When interspecies abundance relationships were investigated at a larger spatial scale, they were found to be spatially structured, and suggested evidence for interspecific competition between Red-headed Woodpeckers and starlings, and niche differentiation between Red-headed and Red-bellied Woodpeckers. This research demonstrates the importance of multi-scale, multi-factor studies when determining threats for species-at-risk and will help in the development of conservation, management, and policy-making decisions for the species.