Barnacle geese wintering here spend less and less time caring for their young. Moreover, geese stay here longer and longer before migrating to breeding grounds in Russia. Goslings make use of this 'extra' time to explore their surroundings.
Birds of prey
Migratory behaviour in geese is culturally determined, i.e. they learn from their parents. Such behaviour has changed tremendously in the last decades. Geese migrate nowadays only in mid May, a month later than in the 1980's. Jonker says that this is due to less favourable conditions along the way. Reduced food supplies and more birds of prey make it more attractive for geese to stay longer in our country. This is shown in his model studies.
In search of
Jonker next examined if a longer stay in the Netherlands can cause parents to take longer care of their young. This is not the case. What's more, parents spend less time caring for their young. Jonker thinks that geese do that for their own good. 'Young geese which are weaned off their parents can find their own way about in search of new territories.' The more time they have, the more chances they have of finding new breeding grounds.'
'From the point of view of the fitness of the parents, this is a positive development', Jonker thinks. 'The young explorers do have a bigger chance of perishing, but if the going is good and a young goose becomes the founder of a new colony, its parents can cash in on this too. It can therefore be beneficial when parents let their young ones roam about at an early stage.' Moreover, migrating parents are not the only ones who take shorter care of their young; those who stay do that too. The latter go to the extent of caring twenty percent less for their young than those who migrate. Jonker says that this shows an extremely quick adjustment to their new status as 'stayers'.