SIGNIFICANCE OF BACK COLOR IN TERRITORIAL INTERACTIONS IN THE AUSTRALIAN MAGPIE

In eastern Australia, two forms of the Australian magpie occur: a whit e-backed form and a black-backed form. These two forms hybridise acros s northern Victoria and into South Australia. In this study the respon se of territorial magpies to caged intruders was examined. Pairs of ad ult male magpies were introduced into territories. Both were adult bla ck-backed birds, but in each case one of them had its back painted whi te. The pair was introduced to each territory twice, with the bird tha t was painted white differing between times. The experiment was run in a population of black-backed birds and a population in the hybrid zon e containing white-backed, black-backed and hybrid birds. In both case s, the residents were more aggressive towards the intruder with the wh ite-back than they were to the black-backed intruder. We suggest that this may be because a white-backed bird posed more of a threat to resi dents than a black-backed bird.