Habitat Use by Three Breeding Insectivorous Birds in Declining Maple Forests

Abstract

We studied population variability and habitat use of the Least Flycatcher (Empidonax minimus), the Red-eyed Vireo (Vireo olivaceus), and the Black-throated Blue Warbler (Dendroica caerulescens) in sugar maple (Acer saccharum) forests of southern Québec in various state of decline. The Least Flycatcher was the most abundant species (1.7 pairs/ha) over the three-year study, although numbers were lower and showed higher interannual variability in declining stands compared to healthy stands. The flycatcher established its territory in areas where trees were tallest, sugar maple was in nearly pure stand, and sub-canopy was sparse. The Red-eyed Vireo (1.2 pairs/ha) was ubiquitous and populations were stable in all study sites regardless of decline. The Black-throated Blue Warbler, less abundant (0.4 pairs/ha), colonized areas of the stand that offered a high density of shrub growth under a closed canopy in both declining and healthy sites. Except perhaps for the flycatcher, there was no clear association between population change or pattern of habitat use and the level of forest decline in these three species. Confounding factors such as predisposing life-history characteristics and large scale population changes may explain some of our results.