Vegetation Structure, Food Supply, and Polygyny in Bobolinks (Dolichonyx Oryzivorus)

Abstract

Territories of polygynous male Bobolinks averaged higher percent cover of several forb species than did those of unmated males. Some differences were also found between territories of polygynous and monogamous males, but not in all years. These differences were associated with differing soil moisture conditions on the various male territories. Vertical density of all vegetation types, vegetation biomass, and grass height were not correlated with the number of females attracted to each territory. Observed vegetation differences do not explain why some territories attracted two females while others attracted only one. Caterpillars constitute a major component of nestling diet. Caterpillar densities were higher on polygynous male territories than on adjacent, physiognomically similar monogamous male territories in mesic habitat. They were also higher on polygynous male territories than on physiognomically similar bachelor male territories in dry habitat. Grasshopper densities were higher on polygynous male territories than on monogamous male territories in mesic habitat, but not at the time second—mated females selected territories. They were lower on polygnous male territories than on monogamous male territories than on habitat. The nesting success of second—mated females was lower than that of first—mated females primarily because of higher nestling starvation. It is concluded that polygyny occurs in Bobolinks because it enables females to breed in areas with more abundant food resources.