Relationships of Food to Spatial and Temporal Breeding Strategies of Mallards in Sweden

Abstract

The function of poor and rich breeding habitats of mallards (Anas platyrhynchos) was studied in an oligotrophic forest lake area in southwestern Sweden during 1975-79. The lakes were ranked according to an increasing degree of fish competition for food. Mallard pair density during egg-laying was highest in small lakes lacking fish. From ice breakup until June, adults and larvae of water insects formed abundant potential food for laying female ducks. However, the number of some invertebrate groups, and especially their mean individual size, was lower in lakes containing fish. Duckling hatching coincided with the peak of insect emergence. Experimentally-released young ducklings obtained significantly more food in lakes without fish. Although the size of the emerging insects increased during the duckling hatching period, flying insects were significantly smaller in lakes with fish. The size and number of food items for laying females and small ducklings were reduced because of fish competition. During other phases of reproduction when the protein demand was lower, the seed and vegetative production was adequate. As a result, there is a shift between different food resources and the breeding mallard may use two types of lakes, the hatching lake and the rearing lake. In optimal habitat, breeding mallards adapt well to temporary and fluctuating food resources in a home range composed of lakes with and without fish. These lakes must be managed in different