Greenfinch feeding behaviour and impact on a rapeseed crop in Oamaru,New Zealand

Abstract

Feeding behaviour of greenfinch flocks on a rapeseed crop was both organised and coordinated. The birds caused minor damage to a large number of plants. They ate approximately half of the rapeseeds from the pods they attacked, and the remaining seeds subsequently fell to the ground. Ripe pods were preferred, and early-ripening plants sustained the heaviest damage. Seed loss calculations from transect data were unsatisfactory because of the high variability of damage levels. Maximum consumption estimates (6.8 g rapeseed per bird per day) and the feeding pressure exerted over the damage period indicated a total seed loss over 16.2 ha of 1.44 tonnes. Earlier planting of the rapeseed crop is suggested as the best method of reducing damage due to birds.