Effects of feeding patterns on body mass loss in moulting Greylag Geese Anser anser

Abstract

Capsule Body mass loss was mainly affected by daily travel distance between roost site and feeding patches. Aims To determine the effects on the rate of body mass loss caused by differences in daily travel distance, frequency of disturbance events and return intervals to feeding patches. Methods A stochastic model was constructed using empirical data on daily energy intake and expenditure to predict daily body mass change in moulting Greylag Geese. Results The model predicted that male and female Greylag Geese would lose on average 35 g and 31 g/day, respectively, corresponding to an overall body mass loss of 1085 g and 961 g during the 31-day moult period. Model simulations showed that the frequency of disturbance events did not affect daily energy budgets of geese provided that geese remained on the feeding areas. Even in the absence of severe disturbance events on the study area, daily travel distance potentially ranged between 0 and 6 km, and differences in this distance were shown to have a significant impact on daily body mass loss. The model predicted that the difference in daily travel distance between 0 and 6 km was equivalent to a daily body mass loss of 1.7 g (a 5% change), or 53 g throughout the moult period. It would be most profitable energetically for geese to completely avoid feeding and remain at the roost throughout the moult period as they could thus reduce their daily body mass loss by up to 7.3 g (20%). Conclusions Geese were never observed to remain at the roost site all day, probably because they needed to fulfil nutritional needs other than those for energy (e.g. protein or possibly specific amino acids for feather renewal). The importance of keeping moult sites free from disturbance was confirmed as disturbance events that displace geese away from feeding areas would impose further increases in daily travel distance and hence body mass loss.