Polygyny in the Dickcissel

Abstract

The mating patterns established in a color-marked population of wild dickcissels, Spiza americana (Fringillidae: Passeriformes) were studied during the summer in Kansas. There was an equal number of males and females in the breeding population. Daily censuses revealed that an average o f 42% of the males were unmated, 40% were monogamously mated, and 18% were polygynous. The territories of mated males were significantly larger than those of mateless males, but there was no difference in size between the territories of monogamous and polygynous males. The territories of unmated males were restricted in the vertical development of the vegetation, and the per cent coverage by f orbs in these t erritories was less than in the territories of mated males. The adaptive advantage of polygyny in the dickcissel appears to be based upon the differential availability of nest sites between the territories of the males. The territories of mateless males do not provide sufficient nesting substrate. Since a female is not preempted by another female already being mated to a male holding a territory wherein suitable nesting cover is available, she is not prevented from nesting. Polygyny allows all available females the chance to reproduce.