Numbers and Arrival Dynamics of Communally Roosting Magpies (Pica Pica) in the Dendrological Park of the University of Forestry—Sofia, Bulgaria

Abstract

ABSTRACTThis is the first annual study of a Eurasian magpie communal roost in Bulgaria. The roost is situated in the Dendrological Park of the University of Forestry—Sofia. The study was carried out in 2007–2008. We ascertained that magpies used to visit the communal roost all year round. The maximum number of birds recorded on one visit was 1405 birds (December 2007) and the minimum number was 139 birds (July 2007). The number of birds sleeping in the communal roost declined in the beginning of the breeding season because the birds started sleeping in their nests or near to them. The average number of birds sleeping in the communal roost during the summer was 32,33% from these in winter. We suggest these were non-breeding and birds whose breeding territory overlapped with the area of the communal roost. Despite significant fluctuation in the number of roosting birds during different seasons, the arrival dynamics of magpies were markedly uniform across all seasons with the exception of spring. The number of birds increased gradually in the first intervals of the study and they reached their peak in the interval 30–15 minutes before sunset and then decreased similarly. However, in spring proportionally more birds arrived on the roost in the interval 15 minutes before to 15 minutes after sunset without any decrease after sunset. Having arrived on the communal roost before sunset, the magpies perched in the crowns of the tallest trees and concentrated in the highest NE part of the roost (altitude 591 m). In the twilight period the birds were shifting their place to the lowest parts (altitude 587 m) which were highly overgrown with dense shrubs. We suggest that the Park has become important for the magpie because of lack of exploitation and we think that returning the intensive exploitation might force the birds to change the roost.