Correlations in abundance of grassland songbirdsand prairie butterflies

Abstract

During 1992–1997, transect surveys simultaneously counting three declining grassland songbirds and all butterfly species were conducted at 109 prairie grasslands in Illinois, Iowa, Minnesota, Missouri, North Dakota, and Wisconsin, USA. Pairwise correlations in abundance between a songbird and a butterfly species were performed with the three songbird species—Henslow's sparrow Ammodramus henslowii, grasshopper sparrow A. savannarum, and dickcissel Spiza americana—and 17 butterfly species, chosen because they were the most frequently observed butterflies in each of three ecological groups (prairie specialist, grassland, generalist) or because they were taxonomically close to the prairie specialists in analysis. Butterfly species in the most restrictive ecological group (specialists) significantly and positively correlated most strongly with the three songbirds, especially at the scale of the entire study region and in subregions where both species in the correlation were more abundant. Grassland butterflies (occurring widely in native prairie and old fields) and generalist butterflies were similarly lower than specialists in degree of covariance with the birds. Correlations of the birds as a group with all observed butterfly individuals in each of the three ecological groups showed similar patterns. Other studies have shown that diversities of distantly related animal groups may not correlate well among habitats and regions. But this study suggests that, within a habitat and region, conservation programs benefitting grassland birds can be favorable for co-occurring prairie-specialist butterflies and that certain bird and butterfly species can be effective indicators of each other.