SUCCESS OF MIGRATORY SONGBIRDS BREEDING IN HARVESTED BOREAL FORESTS OF NORTHWESTERN NEWFOUNDLAND

The consequences of forest harvest to birds nesting in spatially and temporally dynamic landscapes are poorly understood. The boreal forests of Newfoundland have a low density of nesting birds, are naturally heterogeneous, and experience extreme annual variation in weather. Against this backdrop, we tested whether breeding success of passerines was affected by forest harvest or whether natural heterogeneity masked potential consequences of harvesting. During 2004 and 2005, we monitored 98 nests and banded 439 hatch-year (HY) birds of three migratory passerines in landscapes that varied in the extent of natural or human-induced heterogeneity: the White-throated Sparrow (Zonotrichia albicollis), Yellow-rumped Warbler (Dendroica coronata), and Blackpoll Warbler (Dendroica striata). We monitored nest-initiation date, clutch size, hatching success, nests' daily survival rates, fledging success, and productivity (ratio of HY to adults captured) relative to proportion of forest harvested within radii of 20 m (local scale), 115 m (neighborhood scale), and 1250 m (landscape scale). Local habitat and year significantly predicted nest-initiation date. Hatching success, fledging success, and productivity were significantly influenced by year and proportion of harvest at all scales, although associations varied by species. Nests' daily survival rates were significantly related to proportion of harvest at all three scales for the White-throated Sparrow; for all species they were consistently higher in 2005, and the direction of the harvest's effect differed by species. Our results reveal that larger scales are important later in breeding and that spatial and temporal heterogeneity may not only conceal consequences of forest harvest, they may also have complex interactions that make predictions difficult in these dynamic landscapes.