Many organisms use both vegetation structure and social cues in selecting habitats. Many species of songbirds use the presence of breeding conspecifics as a social cue and sign of habitat quality, and can be induced to settle in unoccupied habitats by artificially broadcasting breeding song, a process referred to as “conspecific attraction”. In our study, we tested response to conspecific attraction a low-density population of the threatened Golden-winged Warbler (Vermivora chrysoptera) in Highland County, VA. Response to broadcast song was observed, with a modest increase in mean male abundance at survey points within 250 meters of treatments, and mean abundance decreasing outside of this range throughout the study area. Recruitment to conspecific playback was lower in our study than observed in previous research on high-density systems. Our results suggest more research is needed of the effectiveness of conspecific attraction in low density species and that its use should be tailored to the spatial and demographic conditions of the managed population.

Adaptation to local environments via natural selection is a powerful mechanism for population divergence and likely one of the primary causes of speciation. To understand how specific habitats shape local adaptation, it is helpful to study closely-related populations from widely differing ecosystems that have not had sufficient time to diverge by genetic drift. Throughout the following chapters I examine the distribution of morphological, behavioral, and reproductive phenotypes within and between two subspecies of the swamp sparrow. These two populations, the tidal salt marsh endemic Melospiza georgiana nigrescens and the nominant inland subspecies, M. g. georgiana were incompletely isolated from each other following the retreat of the Wisconsin glaciation. Since that time the increased nest predation, temperature, season length, salinity and tidal flow of the coastal marshes relative to inland wetlands has resulted in a number of adaptations among coastal sparrows due to natural selection, sexual selection, and phenotypic plasticity. Specifically I examine the habitat preferences of the coastal plain swamp sparrow, the difference in clutch size between the two subspecies, the rates of extrapair fertilization relative to male quality, the ecosystem-specific interactions between natural and sexual selection on plumage badges, and the role of conspecific attraction in nest placement. The environmental differences of the tidal salt marsh have played strong roles in the local adaptation and divergence of coastal plain swamp sparrows from their freshwater ancestors. Many of these divergent mechanisms may be similar among other tidal marsh endemics, although some (especially those related to sexual selection) may be specific to the swamp sparrow. In general, however, we see that the added environmental challenges of tidal ecosystems strongly alter selection regimes on a terrestrial vertebrate inhabiting this dynamic ecotone. The swamp sparrow system can further increase our understanding of how the interplay between environmental resources, sexual selection, and natural selection affects the local adaptations leading to evolutionary divergence. / Ph. D.

Many grassland songbird species exhibit sensitivity to patch size in North America’s fragmented prairie ecosystems, but the mechanisms explaining this area sensitivity are not well understood. I tested the effects of patch size and artificial conspecific location cues (song playback and decoys) on grassland songbird abundance in 23 northern tall-grass prairies in Manitoba, Canada, in 2010 and 2011. Richness and relative abundances increased with patch area; this effect was not explained by differences in local habitat structure, patch configuration, and adjacent matrix. Artificial cues elicited putative territory prospecting in small, previously unoccupied treatment patches from two focal species, Savannah Sparrow (Passerculus sandwichensis; n=3 treatment sites) and Le Conte’s Sparrow (Ammodramus leconteii; n=4 treatment sites), but not in control patches (n=3 for both focal species). Social information may influence the focal species’ settlement decisions, but the lack of permanent settlement response suggests social cues are unable to reverse their area sensitivity.

Many grassland songbird species exhibit sensitivity to patch size in North America’s fragmented prairie ecosystems, but the mechanisms explaining this area sensitivity are not well understood. I tested the effects of patch size and artificial conspecific location cues (song playback and decoys) on grassland songbird abundance in 23 northern tall-grass prairies in Manitoba, Canada, in 2010 and 2011. Richness and relative abundances increased with patch area; this effect was not explained by differences in local habitat structure, patch configuration, and adjacent matrix. Artificial cues elicited putative territory prospecting in small, previously unoccupied treatment patches from two focal species, Savannah Sparrow (Passerculus sandwichensis; n=3 treatment sites) and Le Conte’s Sparrow (Ammodramus leconteii; n=4 treatment sites), but not in control patches (n=3 for both focal species). Social information may influence the focal species’ settlement decisions, but the lack of permanent settlement response suggests social cues are unable to reverse their area sensitivity.