Lewis’s Woodpecker nest success and habitat selection in floodplain and burned forests in western Montana

Lewis's Woodpecker (Melanerpes lewis) is a common breeder of the Bitterroot Valley and across western Montana, yet populations have been dwindling across its range since the 1970s. We do not know the causes behind this species downfall, but some researchers have found some populations exhibit low nest success. Systematic selection of nest sites with low success can occur when individuals cannot adapt fast enough to changes in their environment and cause populations to decline at a broader level. Hence, we tested the maladaptive habitat selection hypothesis in Lewis's Woodpeckers in the Bitterroot Valley by comparing Lewis's Woodpecker nest-site selection and nest success between cottonwood and burned conifer forests. We predicted that maladaptive selection would occur if we found the higher breeding density of Lewis's Woodpeckers in the forest type associated with the lowest nest success. Lewis's Woodpecker adult density in cottonwood forest was almost three times the density than in burned forest (Fig. A). In contrast, Lewis's Woodpecker had lower nest success in cottonwood than in the burned forest (Fig. B). However, nest success was still relatively high overall and promoted stable populations in our study area.

Furthermore, our results suggest that Lewis's Woodpeckers who initiate nests earlier in the season are more successful than later initiated nests (Fig. B). We observed that Lewis's Woodpeckers in cottonwood forest competed for cavities with European starlings (Sturnus vulgaris). The competition for nests early in the season may dictate nest success outcomes in an arms race between adult survival and juvenile survival. On the one hand, early returning adults at breeding grounds may better secure a nest site and successfully rear offspring against. But, on the other hand, the early returning adults may risk increased mortality from predation risk due to low canopy cover before the trees leaf out and lower foraging availability before insects and berries abound. We also found that cottonwood forests contain a much higher density of dead trees and snags than burned forests. Snag availability provides nesting substrate (i.e., cavities) for many cavity-dependent species. Our results suggest that land managers at Lewis's Woodpecker breeding grounds should promote the retention of tall trees and snags.