The effect of poisoning on the movement of rooksCorvus frugilegusL. in southern Hawke's Bay, New Zealand

Abstract

Abstract The effect of poison bait at a rookery on the movement of rooks (Corvus frugilegus L.) was studied using marking and radiotelemetry at five rookeries in southern Hawke's Bay, New Zealand. In November 1987 and 1988, before poisoning, rooks were retrapped near rookeries other than those near where they were marked, showing that feeding areas overlapped. Birds marked in 1987 were located north and north-east of original rookeries in 1988. In spite of extensive searches throughout the study area, no southward movement was seen. Between July and November 1988, 12 marked rooks moved to rookeries in a south-east direction. Poisoning at the rookery in November 1988, using DRC-1339, killed 38 rooks, including 10 birds marked near that rookery and 4 marked near other rookeries. At least six marked birds and one with a transmitter survived, as well as three birds with transmitters released after the poisoning. These 10 rooks were seen at other rookeries in 1989, including 2 marked rooks that moved 3 km south-east. The surviving rook with a transmitter moved 4km south-west. A search of rookeries south of Dannevirke failed to reveal marked rooks, so there was insufficient evidence to suggest that poisoning was responsible for the recent southward extension of their range.