Polygyny in the european starling: effect on female reproductive success

Abstract

Polygyny among European starlings, Sturnus vulgaris, a monoterritorial, colonially breeding passerine, was studied for 4 years. In nestbox colonies around Antwerp, Belgium, primary females did not breed less successfully than monogramous females. No aggressive physical interactions between primary females and prospecting secondary females were recorded. Some primary females ‘interfered’ (i.e. flew into the tree where the secondary nestbox was situated) when their mate was demonstrating a secondary nestbox to a prospecting female, but were chased off by their mate almost every time they interfered. Primary females ‘interfered’ more frequently before completing their clutch than afterwards. Secondary females generally fledged significantly fewer young than monogamous females. Secondary females could be classified into two categories. Category I females did not have the opportunity to select bachelor males at the time of mating, and these secondary matings may therefore be explained by the femalebiased sex ratio at that time. Category II females, which could choose between mated and unmated males, fledged only 68% as many young as did simultaneously laying monogamous or primary females and their young weighed less. These results conflict with the predictions of the polygyny threshold model and the sexy son hypothesis, that secondary females should gain evolutionary advantage in either the short or long term. On the present evidence, it is not clear why category II females mated with already-mated males. Circumstantial evidence that they might have been unaware of the male's marital status at mating is presented.