Ken A. Elliott

Predation by Bears on Woodpecker Nests: Are Nestling Begging and Habitat Choice Risky Business?

ABSTRACT. We evaluated hypotheses explaining risk of predation by American Black Bear (Ursus americanus) at 418 Yellow-bellied Sapsucker (Sphyrapicus varius) and Hairy Woodpecker (Picoides villosus) nests, on the basis of nestling begging and nest-site habitat features in Algonquin Provincial Park, Ontario. Ninety-three percent of Yellow-bellied Sapsuckers in stands dominated by Sugar Maple (Acer saccharum) nested in Sugar Maple or American Beech (Fagus grandifolia) trees that were dead or in declining health, whereas 86% of Yellow-bellied Sapsuckers in stands dominated by aspen (Populus spp.) nested in Quaking Aspen (P. tremuloides) that were in declining health. Black Bears depredated 17% of 315 nests of Yellow-bellied Sapsuckers in Sugar Maple stands, which accounts for 71% of all Yellow-bellied Sapsucker nest failures. Only 1 (2%) of 46 Hairy Woodpecker nests in the same Sugar Maple stands was depredated by a bear. None of 51 Yellow-bellied Sapsucker nests in aspen stands was depredated. In Sugar Maple stands, daily nest survival of Yellow-bellied Sapsucker nests was lowest when nestling begging calls were loudest and carried the farthest, in more recently harvested stands, and in trees other than American Beech (mostly Sugar Maple). Nest substrates were hardest at Hairy Woodpecker nests, followed by successful Yellow-bellied Sapsucker nests in American Beech and Quaking Aspen; Yellow-bellied Sapsucker nests were softest in stands that had been harvested within the past 30 years. Our study suggests that the risk of predation by American Black Bears at woodpecker nests is a combined function of nestling begging calls, which attract bears to the nest, and nest habitat characteristics, which influence accessibility to the interior of the cavity.

Effects of Forest Management on Postfledging Survival of Rose-Breasted Grosbeaks (Pheucticus ludovicianus)

ABSTRACT. Many studies have examined the effects of forest fragmentation and management on songbird nesting success, but few have quantified postfledging survival, which is a critical component of population productivity. In 2005–2006, we estimated daily postfledging survival of Rose-breasted Grosbeaks (Pheucticus ludovicianus) by radiotracking 42 fledglings in forest fragments that had been managed by single-tree selection, by diameter-limit harvest, or as reference (not harvested for at least 25 years). Survival probability over the 3-week fledgling period was 0.62, and 86% of total fledgling mortality occurred during the first week out of the nest. Despite large differences in forest structure between forest management treatments, there was no effect of forest treatment on fledgling survival. Date of fledging, shrub cover, and patch size also had limited influence on fledgling survival. For all sites combined, females produced an estimated 0.23–0.37 recruiting daughters per year for the worst- and best-case scenarios of female fecundity and annual juvenile survival, which is lower than the expected annual mortality rate of breeding females (0.40–0.55). Even reference sites did not produce enough offspring to offset annual female mortality, which suggests that forest fragments in this region are population sinks.

NEST-SITE SELECTION OF ROSE-BREASTED GROSBEAKS IN SOUTHERN ONTARIO

Abstract Rose-breasted Grosbeaks (Pheucticus ludovicianus) commonly breed in the deciduous woodlands of southern Ontario, but have become a species of conservation concern due to recent population declines (2% per year in Ontario from 1966 to 2004). We investigated whether habitat alterations may be contributing to these declines through decreases in nest survival at nest and randomly selected sites in 23 woodlots varying in the intensity of partial harvest. Rose-breasted Grosbeaks consistently selected nest sites with more sapling cover, less canopy cover, and a lower surrounding basal area than available. The best supported model of daily nest survival included a measure of nest concealment, with the top 15 models containing nest concealment indicating higher nest survival rates at less concealed nests. Model-averaged estimates produced positive slopes for canopy cover, sapling cover, and nest height indicating higher survival at higher canopy cover, sapling cover, and nest height. Heavy-cutting practices appear to create woodlots that act as ecological traps. These woodlots provide “preferred” nest sites that result in low nest survival probabilities for the Rose-breasted Grosbeak.