Seasonal Changes In Group Size And Foraging Activity In An Urban Population Of Magpies ( Pica Pica )

Abstract

We studied seasonal variation in group size and feeding activity in an urban population of Magpies in Zielona Góra, Western Poland. Each month from 1984 to 1987 we counted the species along a 10 km transect across the city and noted the number of single birds, pairs and flocks as well as flock size. In 1999 and 2000 we regularly observed Magpies foraging on the lawns of a park of Zielona Góra and recorded the number of pecks, as a measure for feeding activity. Magpies were most often encountered as single birds in April and May, as pairs in March, and in flocks in August. This pattern is predominantly dictated by the constraints of the breeding season and by reproductive success. The mean flock size was highest in August. Pecking rate showed a minimum in the summer months, with no sex-specific difference. However, males were much more active in foraging during winter, probably due to their larger body size and the respective higher energetic requirements.