The feeding ecology and behavior of wigeon (Anas penelope)

The aim of the project was to investigate the behavioural and physiological strategies used by wigeon to maximise their nutrient intake during winter. The reasons for selecting this species were its totally herbivorous diet, its simple digestive physiology and its small body size, all of which should lead to problems in gaining sufficient nutrition during the winter. The daily energy expenditure of this species was estimated from faecal output studies to be 150 kcal bird-1 day-1. This figure was compared with estimates for the larger grazing geese in order to assess the effect of body size on energy intake. The strategy of feeding for long periods (as much as 17 hours per day) to increase food intake seems to be very important in this species. Feeding site selection was investigated as this is an obvious way to increase nutrient intake. Wigeon show clear preference for particular feeding sites both in terms of amount and timing of use. Grass biomass, grass protein content and proximity to water are all important factors in site selection, reflecting the requirements for efficient feeding and safety from predators. Fertilization of a site increased its use by a factor of 2.5 A spectrophotometer for grass biomass assessment was designed and built for this part of the work. The behavioural changes resulting from differences in grassland type were studied. An increased biomass (and protein content) of grass on a site resulted in higher peck rates, slower walking rates and increased defaecation rates. These changes increased the efficiency of food intake on high biomass areas and allowed birds to exploit optimally a patchy food resource. The effect of grass height on peck rate was also investigated. Wigeon grazing has a great effect on the biomass, height and spring production of grass on their feeding sites. Of more importance is the fact that winter grazing can signficantly affect the protein content of grass in the spring. This effect is caused by the increased turnover rate of leaf material on grazed sites. The pressures leading to the tight feeding flocks, characteristic of this species, were studied. The flock-feeding strategy is likely to be important for nutrient intake since it leads to an increased protein intake in spring, and may also allow information regarding good feeding sites to be exchanged. Studies on vigilance activity showed that a decrease in vigilance time is important in small flock formation. This would have advantages for both feeding efficiency and safety from predators. The reduced likelihood of individual predation is also important in producing larger flocks. Finally, the physiology of wigeon digestion was studied. Wigeon have a very rapid throughput time and a low digestive efficiency. The storage of protein in the form of gut -tissue may also be important for breeding reserves in female birds.

Level dc:type.qualificationlevel

PhD

Grantor dc:publisher.institution

University of Glasgow

Year dc:date.issued

1985

Author dc:creator

• Mayhew, Peter Watts

• QL Zoology

Language dc:language

en