Co-occurrence with Greylag Geese Anser anser and other factors affecting vigilance in White‑fronted Geese Anser albifrons during their spring staging in Central Europe

Abstract

Vigilance, a crucial factor affecting the behaviour of birds, is key to the safety of migratory animal flocks against predators and other threats. We examined the vigilance of White-fronted Geese in the Biebrza Basin (NE Poland), one of their major stopover sites in Europe. The study took place during their spring staging, from the end of February until the beginning of April. We found that the vigilance of White-fronted Geese decreased in the centre of mixed flocks with Greylag Geese. This may be associated with the larger size and wider field of view of Greylag Geese, as well as their territorial behaviour, as some of them belong to the local breeding population. White-fronted Geese can benefit from the group-size effect when they form larger flocks. In the presence of a vigilance stimulus, the individuals in the centre of a flock raised their alertness levels. As the probability of detecting danger is higher in large groups, flock size negatively affected the birds’ vigilance. Owing to their different experience and roles (adults care for their broods by being vigilant), adult birds appeared to be vigilant on both grassland and arable land, whereas immatures were vigilant only on arable land, where exposure to predatory pressure was greater. We believe that the lower level of vigilance of White-fronted Geese in large and mixed flocks may give them more time for foraging and, therefore, improve their chances of survival and breeding success during the oncoming spring.