Ecology and behavior of migratory songbirds during stopover periods

Stopover habitat quality may influence the success of migration and ultimately affect songbird reproductive success or survival. Despite this, spatio-temporal patterns of stopover habitat use, relative quality, habitat relationships, and selection mechanisms are inadequately known within inland North America. During spring, breeding, and fall 1997–1999 in Pennsylvania, I surveyed birds within forest interior, forest-agricultural edge, and suburban, pole-stage, and early successional forest habitats. I used abundance, species richness, and migrant foraging behavior to identify important habitats. I measured leaf development and microhabitat to assess important habitat characteristics. Habitat use varied by year in both spring and fall. In spring, edge-dominated suburban forest and forest-agricultural edge had higher abundance of transient species and guilds and higher transient richness than early successional and pole-stage forests. Transient individuals of migrant species that bred locally primarily used edge-dominated habitats. During fall, forest-agricultural edge and early successional forest had higher abundance and richness of Nearctic-Neotropical migrants. Fall abundance and richness of mature forest-breeding migrants were highest in forest-agricultural edge, whereas early successional-breeders had highest values in breeding habitat. High prey attack rate and glean rate and low sally rate of Yellow-rumped Warblers (Dendroica coronata) in forest-agricultural edges suggested that food availability and quality were greater in that highly used habitat, relative to suburban forest and forest interior. However, high spring use of suburban forest by this species was not clearly related to foraging behavior. Transients were positively associated with >38 cm diameter trees and percent shrub cover in spring and fall. Canopy leaf development in early spring was negatively associated with transient abundance, suggesting preference for sites with trees at budburst, when lepidopteran larvae should be most abundant. However, there were no main effects of fruit availability on frugivores or Nearctic-Neotropical migrant abundance. The conservation value of forest edges and early successional forests may be higher than currently realized because these habitats are important to both early successional breeding birds and stopover migrants of mature forest-breeding species. I recommend maintaining or creating quality stopover habitats where a successful balance between needs of forest interior, forest edge, and early successional associated species can be achieved.