White-headed woodpecker nesting habitat at multiple spatial scales: Are habitat preferences adaptive?

Abstract

Ecological theory predicts that animals will select habitats for breeding that confer an adaptive advantage through increased reproductive success. We therefore expect to see congruence between habitat preferences and measures of fitness. We studied abundance, nest site selection, and nest survival in white-headed woodpeckers (Picoides albolarvatus) in four forest types along an elevational gradient in the southern Sierra Nevada, California. Our primary objective was to ascertain what habitat features white-headed woodpeckers were selecting for nesting and at what scale, and whether those choices translated into increased reproductive success. We examined sets of models that included abiotic factors and habitat at three spatial scales: nest site (0.04 ha), local (~1 ha), and home range (~125 ha). White-headed woodpeckers were more abundant at higher elevations, with low abundance in low-elevation ponderosa pine forest, moderate abundance in mid-elevation mixed conifer forest, and reached their highest abundance in true fir habitat before becoming rare in high-elevation lodgepole pine forest. They both selected for and nested more successfully at higher elevations in true fir forest. White-headed woodpecker nesting ecology in the Sierra Nevada demonstrated a mixed pattern of congruence between characteristics important to nest habitat selection and nest survival. We found congruence for abiotic and home range scale models (agreement between preferences and nest survival), indicating adaptive selection. At the landscape scale, White-headed woodpeckers selected closed-canopy conifer forests with abundant edges. Habitat preferences at the nest site scale were negatively related to nest survival, suggesting maladaptive habitat selection at this scale. White-headed woodpeckers selected open forest with higher basal area of snags compared to available sites, but nest survival was higher in forest with higher canopy closure and lower basal area of snags. Local scale models were weak and did not help clarify habitat relationships. Our results highlight the importance of considering multiple spatial scales when examining habitat preferences. The primary management considerations for white-headed woodpecker habitat include retention of large, suitable snags and the need to consider forest heterogeneity. The close association with ponderosa pine forests and large-seeded pines found over most of their range did not hold in the Sierra Nevada, where white-headed woodpeckers were most abundant in true fir forests and selected and nested more successfully in true fir forests. Habitat models developed outside the area for which they were developed should be validated before they are applied to other locations.