DICKCISSELS AND CROP DAMAGE IN VENEZUELA: DEFINING THE PROBLEM WITH ECOLOGICAL MODELS

Abstract

The Dickcissel (Spiza americana) is a neotropical migratory bird that has declined 40% over the years since it was first censused in 1966 throughout its breeding range in North America. The decline has been caused by excessive overwinter mortality resulting from control programs on the wintering range in Venezuela, where the bird is considered to be an agricultural pest. Rice and sorghum farmers kill the birds because they damage crops, but the relationship between the birds and crops has been poorly described. We use demographic, physiological, and ecological data to develop descriptive models that allow us to understand the scope of Dickcissel crop damage. These models show that Dickcissels actually consume relatively small proportions of Venezuela's rice and sorghum production, suggesting that farmers' general perceptions of the magnitude of the problem are exaggerated, even though some individual farmers do suffer greater than average losses. Our data and models can be used as the basis for negotiating a solution to the conflict between farmers and Dickcissels.