Density, Abundance, and Habitat Associations of the Inland Swamp Sparrow (Melospiza georgiana georgiana) in Iowa

摘要

Wetlands continue to decline throughout North America and the Prairie Pothole Region, thus emphasizing the importance of understanding population trends and habitat associations of wetland species to ensure effective conservation and habitat management of those species. We estimated density and abundance and evaluated habitat associations of the Inland Swamp Sparrow (Melospiza georgiana georgiana) in Iowa. We conducted standardized distance sampling surveys for Swamp Sparrows and measured habitat characteristics at 307 wetlands in two regions of Iowa in 2009 and 2010. We used Program Distance to model detection probability and estimate region-specific breeding densities of Swamp Sparrows at Iowa wetlands. We then extrapolated density estimates to the total area of wetlands in each region to obtain estimates of breeding abundance. We correlated Swamp Sparrow counts to nine habitat variables using Poisson regression in Program R. Swamp Sparrow counts were positively correlated with percent cover of cattail (Typha spp.) and water depth (cm) and negatively correlated with percent cover of woody vegetation, vegetation size (m), and wetland size (ha). We estimated breeding densities of Swamp Sparrows to be 1.488 birds/ha (95% CI = 1.308 − 1.692) in region 1 (Des Moines Lobe landform) and 0.041 birds/ha (95% CI = 0.006 − 0.275) in region 2 (remainder of the state). Our results, in comparison to those of other studies, indicate that Swamp Sparrows associate with a variety of wetland characteristics depending upon what is available. Swamp Sparrows are relatively uncommon breeders in Iowa, and our work confirms that most occur in the Des Moines Lobe landform in north-central and northwestern Iowa. Biologists and land managers should incorporate our findings on this species’ habitat associations into management activities to ensure that Swamp Sparrow populations persist into the future.