The effects of partial cutting on the Rose-breasted Grosbeak: abundance, food availability, and nest survival

Abstract

Periodic partial harvesting of trees is an important economic activity within the highly fragmented woodlands of southern Ontario. We studied the population density, age structure, food abundance, productivity, and nest survival of Rose-breasted Grosbeaks (Pheucticus ludovicianus) nesting in 35 deciduous woodlots with varying intensities of harvest. Heavily cut woodlots contained higher densities of territorial males and greater abundances of fruit-bearing shrubs compared with standard cut and reference sites (uncut for >13 years). Results based on insect sampling were mixed, depending on the sampling technique and sample date. All treatments were demographic sinks, with populations in this landscape showing annual declines of 19%–24%. Though the proportion of parasitized nests tended to be higher in heavily cut sites, harvesting had little effect on nest survival, nest initiation dates, clutch size, age structure, or the number of young fledged from a successful nest. Our results indicate that within the fragmented woodlots of southern Ontario, partial harvesting does not further degrade breeding habitat for Rose-breasted Grosbeaks. However, further research is needed to determine the underlying causes of population declines.