Within-sason divorce rate in an urban population of European Blackbird Turdus merula

摘要

The within-season divorce rate of the European Blackbird Turdus merula was studied in 1997-2003 in two city parks in Szczecin (NW Poland). Within the population studied, 14 and 11% of pairs in each of the park were observed to divorce, the early-mated pairs divorcing more seldom (I I and 10%) than the late-mated pairs (48 and 15%). Females that switched males did not pair up with larger males. Individuals initiating the divorce did increase their breeding success, as opposed to the deserted partners. The causes underlying within-season divorces may be divided into the following two groups: usurpation (22%) and. escape from the territory (78%). The frequency of various divorce causes was found to be plot quality dependent. Usurpation caused 39% of divorces in plots having the highest fledgling production, while in areas with poor success only 11% of the divorces had this cause and escape from the territory was predominant. No statistically significant relationships between the within-season divorce rate and the number of single males and the number of broods in a given year was found.