Flock, pair and group living lifestyles without cooperative breeding by Australian Magpies Gymnorhina tibicen

Abstract

The social behaviour of Australian Magpies Gymnorhina tibicen was studied at Linton in the Manawatu district, New Zealand, from June 1978 to November 1982. Territorial magpies defended all‐purpose areas averaging 5 ha in size, and there was no correlation between territory size and the number of occupants. The mean adult survival rate was 0.85, and average annual productivity was 0.96 juveniles per breeding female. Nomadic flocks formed in the spring and foraged on open, treeless pasture. They mainly comprised 1–3‐year‐old magpies which did not breed. Territories were defended by monogamous pairs, and by groups ranging from three to six individuals. Some territorial groups probably originated in the flock, and may therefore have consisted of unrelated birds. Other territorial groups formed when juveniles did not disperse away from the natal territory, and were called family groups. Non‐breeders did not help at the nest in any group, and there was no difference in the production of young by females breeding in group‐defended territories compared with those in pair‐defended territories. The opportunity to disperse into non‐territorial flocks may have liberated Australian Magpies from cooperation.