The maintenance and consequences of polygyny in Eastern Meadowlarks (Sturnella magna)

Stephanie Leah Brown, Purdue University

Abstract

Polygyny is rare in birds and females sharing a mate may be at a reproductive disadvantage due to increased competition for food on the territory, increased predation risk for nestlings, or reduced male aid in raising young. Females might be compensated for this disadvantage if they mate with males that defend high quality territories or provide high quality parental care. I examined the role of female choice, biparental care, and territory quality in the maintenance of polygyny in Eastern Meadowlarks. Males defend territories averaging over 2.7ha on which between 1 and 5 females nest. A female-biased sex ratio limits most females to mating with already-mated males. Female reproductive success is not diminished for females that mate with polygynous males, probably due to their discrimination among breeding sites. Both male and female reproductive success is correlated with the order in which females initiate their first nests. Females avoid each other temporally, but not spatially; females mate preferentially with unmated males, yet nests were clumped. Male size, as measured by wing length, was variable among males, and female reproductive success increased with the decreasing wing length of their mates. Short-winged males made fewer feeding trips to the nest and may spend more time in mate attraction or nest vigilance. Both male feeding rates and the latency to respond to a model predator varied among males; however, neither measure of parental care strongly influenced either female reproductive success or female choice. Vegetative composition and vertical cover, and arthropod abundance varied among territories. More females settled on territories with a lower proportion of bare ground, and higher proportions of both forbs and insects other than grasshoppers and caterpillars; however, no territory attributes clearly influenced either the order of female settlement or female reproductive success. Predation rates are influenced by gross rainfall and vegetation changes. Female discrimination of breeding opportunities may be based on a compromise between male parental care and habitat quality that shifts under different climatic conditions. Variation among both years and females may obscure any clear patterns of female choice.

Degree

Ph.D.

Advisors

Rabenold, Purdue University.

Subject Area

Ecology

COinS