Effects of single-tree selection harvesting on Rose-breasted Grosbeak (Pheucticus leudovicianus) demography in a northern hardwood forest

Abstract

Single-tree selection harvesting is frequently used in the tolerant hardwood forests of North America, but little is known about how it affects the reproductive success of migratory songbirds. Many songbirds that breed in tolerant hardwoods, including the Rose-breasted Grosbeak (Pheucticus leudovicianus) are experiencing population declines across their breeding ranges. We studied habitat characteristics and reproductive success of Rose-breasted Grosbeaks in stands harvested 0–5, 16–20, and 21–25years previously and in reference stands (un-harvested for >50years) in Algonquin Provincial Park, Ontario, Canada (n=3 per age class). Recently harvested stands had higher cover from regenerative growth and lower sapling, understory, and canopy cover than other treatments, whereas reference stands had higher basal area and sapling cover. Pairing success was significantly lower in the reference stands than in all other post-harvest treatments, and the number of fledglings per successful nest was significantly lower in the reference stands than in the 0–5years post-harvest stands. Density and population growth rate were significantly positively correlated, suggesting that density may be an adequate indicator of habitat quality for Rose-breasted Grosbeaks in forested landscapes. Older males were present at higher densities, initiated their nests earlier, and produced significantly more fledglings per nest than younger males in all treatments. Habitat characteristics did not differ significantly between nests with second-year and after-second-year males, suggesting greater reproductive output of older males was likely due to experience rather than monopolization of better quality territories. We concluded that single-tree selection harvesting was beneficial to Rose-breasted Grosbeaks in our predominantly forested study area. Population growth rates were below replacement levels in the 21–25 years post-harvest and reference treatments, but populations were stable in the younger regenerating stands. Thus, in a continuously forested landscape this species’ declines are probably not attributable to single-tree selection harvesting.