Habitat occupancy patterns of a forest dwelling songbird: causes and consequences

We examined patterns of habitat use and reproductive performance of a migratory songbird, the black-throated blue warbler (Dendroica caerulescens (Gmelin, 1789)), within a 3160-ha forested landscape. We surveyed 371 sites over a 3-year period. Some sites were never occupied, while others were occupied for 1, 2, or 3 years. For these 3 years we found that warbler abundance increased with frequency of occupancy. Additionally, we found that (i) deciduousness and understory shrub density increased with frequency of occupancy; (ii) in 1 of 3 years, food abundance was higher at the most frequently occupied sites; and (iii) nest predators exhibited predator-specific abundance patterns across occupancy categories. We next used occupancy patterns documented in the first 3 years of the study to predict settlement, age structure, and reproductive performance at a subset of sites in the final year of the study. We found that males settled earlier in the breeding season at sites with a high frequency of occupancy. There were no differences in arrival times of females. Additionally, age structure did not vary for either males or females across sites with different occupancy levels. Although we found no difference in mean reproductive output across sites with different occupancy levels, over 50% of the young produced fledged from territories overlapping the high occupancy sites.