Factors Affecting Selection of Nitrogen-Fertilized Grassland Areas by Breeding Wigeon Anas penelope

Abstract

In a choice between different experimental plots, Wigeon initiated grazing bouts in fertilized vegetation plots in late April and early May, but switched to clipped plots at the end of May. There was a positive correlation between the frequency of plots first visited and time spent grazing in these same plots, as well as between the mean length of grazing bouts in different plots and the time spent grazing in those plots. Wigeon spent more time grazing in fertilized plots during the mid afternoon and evening in the early breeding period (late April and early May) than in the late breeding period (late May and early June). The mean peck rates in different plots did not differ during the early period, but later decreased as a result of increasing vegetation height. There was a positive correlation between the mean nitrogen concentrations in leaf tips and time spent grazing. Furthermore, there was a positive correlation between nitrogen concentration and the mean duration of grazing bouts. The extrinsic and intrinsic factors affecting the birds' selection of particular plots during the breeding season are discussed.