Correlations in abundance of grassland songbirds and prairie butterflies

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 Wisco nsin, USA. Pairwise correlations in abundance between a songbird and a butt erfly species were performed with the three songbird species-Henslow's spar row Ammodramus henslowii, grasshopper sparrow A. savannarum, and dickcissel Spiza americana-and 17 butterfly species, chosen because they were the mos t frequently observed butterflies in each of three ecological groups (prair ie specialist, grassland, generalist) or because they were taxonomically cl ose to the prairie specialists in analysis. Butterfly species in the most r estrictive ecological group (specialists) significantly and positively corr elated most strongly with the three songbirds, especially at the scale of t he entire study region and in subregions where both species in the correlat ion were more abundant. Grassland butterflies (occurring widely in native p rairie and old fields) and generalist butterflies were similarly lower than specialists in degree of covariance with the birds. Correlations of the bi rds as a group with all observed butterfly individuals in each of the three ecological groups showed similar patterns. Other studies have shown that d iversities of distantly related animal groups may not correlate well among habitats and regions. But this study suggests that, within a habitat and re gion, conservation programs benefitting grassland birds can be favorable fo r co-occurring prairie-specialist butterflies and that certain bird and but terfly species can be effective indicators of each other. (C) 1999 Elsevier Science Ltd. All rights reserved.