Aspects of the Feeding Ecology of Mallard and Black Swan in a Small Freshwater Lake

Section 1. Limnological and waterfowl food supply characteristics of Pukepuke Lagoon are described. Emphasis is placed on describing how the balance between macrophytes and phytoplankton is established (these two forms of vegetation tend to dominate alternately in the lagoon). The question of whether heavy swan grazing may potentially shift this balance in favour of phytoplankton dominance is examined. Section 2. The year-round patterns of feeding exhibited by mallards are described on the basis of scan counts taken at one or two-hourly intervals from dawn to dusk. These feeding patterns, graphically depicted, are then interpreted and discussed against the background of what is known of the food content of the lagoon. Reference is made to the behavioural and physiological adaptability of the birds, and to the reserve capacity of the wetland complex - not just Pukepuke Lagoon - to sustain them. The relevance of these findings and interpretations, to New Zealand in general is discussed. Section 3. An hypothesis is developed to account for the way in which black swans use various waters in the Pukepuke-centred wetland complex.