Farmers in northern- and mid-Norway are threatening to scale up efforts to scare the birds off their fields, which the geese use as a staging post on their migration north, unless they are compensated for the damage to crops and grassland.
Together with colleagues in Denmark and Norway, Klaassen used data from ringed geese collected between 1991 and 2003 to model the impact of organised scaring of pink-footed geese. They found that any rapid escalation of bird scaring could be catastrophic for the birds, especially for less experienced individuals.
According to Klaassen: "The model predicts that if scaring on a large scale is implemented abruptly, it will have severe consequences for the population because the geese will not have time to adjust their behaviour to their dramatically changed environment. We are already seeing signs of decreasing annual breeding success and decreased summer survival as a result of poor body condition when the geese depart from the spring staging areas. Our model shows that naïve geese have much lower fitness than experienced geese, which are able to anticipate and adapt to changes in their environment."
There are two discrete populations of pink-footed goose: the Greenland/Iceland population, which breeds in Iceland and Greenland and overwinters in Britain; and the Svalbard population. The Svalbard group overwinters in Denmark, Belgium and the Netherlands and migrates to breeding grounds in Svalbard (an archipelago hundreds of miles off the north coast o f Norway) in spring. On their migratory route north, the geese stop to feed on sheep pastures and emerging crops at Vesterålen in northern Norway so that they arrive in Svalbard in good enough condition to breed successfully.
Populations of the goose have almost doubled over the past twenty years, from between 23,000 and 30,000 in the 1980s to 45,000 today. This growth, coupled with loss of natural habitats, has forced geese to break their migration on farmland, and into conflict with farmers.
"While conditions on the breeding grounds have generally remained unaffected by human activities, the staging and wintering grounds have undergone dramatic changes as a result of human development. As a result, most wintering populations have changed from feeding on natural or semi-natural habitats to agricultural land," Klaassen says.
As well as helping to develop strategies to manage the conflict between farmers and geese, Klaassen's model could help ecologists predict how other species might respond to climate change. According to Klaassen: "We need tools to predict how organisms will respond to local and global changes, and such tools would be particularly useful if they could take into account adaptive behaviour. In the case of migratory birds, the implications of environmental change may be particularly difficult to predict because these animals use a succession of sites during their annual cycle."