Polygyny in the European Starling

Abstract

1. The polygynous behaviour of male starlings breeding in nest box colonies around Antwerp, Belgium, was studied for 4 years in order to investigate whether polygyny is a widespread reproductive strategy in this species. 2. The proportion of breeding males occupying more than one nest box ranged from 44% to 72%. Some males (23%) apparently 'preferred' to mate monogamously since they occupied only one nest box despite one or more unoccupied neighbouring nest boxes being available. Generally, the occupation of more than one nest box was not related to arrival date, age or morphological characteristics. 3. On average 39% of breeding males tried to become polygynous. Of these males, 68% tried to attract a second female during the fertile period of their first one. By occupying nest boxes situated close together, male starlings can try to attract a second female at the same time that they guard their first female. Males varied considerably in the number of days they tried to become polygynous (range 2-11 days). However, most (85%) were trying during the laying period. The fact that all males trying to attract an additional female had permanently stopped their attempts at the latest when the nestlings were 10 days old suggests that after this point the possible benefits of trying to attract an additional female are outweighed by the costs incurred from not feeding their young at that time. 4. The frequency of polygyny in the starling was established for the first time and ranged from 20% to maximum 60%. These results indicate that the starling has to be considered as a regular polygynist (exceeding the limit of 5 % of male breeding records). Bigamy was the form of polygyny typical in our study areas. Older males were polygynous more frequently than yearlings, possibly because they alto tried to attract a secondary female more frequently and had higher success than yearling males. As regards arrival sequence, there was no significant difference in the proportion of early and late arriving males that were polygynous. Early males tried to become polygynous more frequently than late males, but did not have higher success. 5. Polygynous males produced significantly more fledglings per year than did monogamous males (7.9 vs 4.6), strongly suggesting that they achieved higher fitness compared to monogamous males. However, so far, accurate measures of the variance in male reproductive success are not possible, since the frequency of successful extra-pair copulations in the starling remains unknown.