The decline on the island is a combination of several factors. The most important are:
- change of habitat, the dunes becomes more vegetated with bushes and trees makes it more suitable for the stronger Marsh Harrier
- because of the change of habitat the total number of Rabbits drops sharply the last years. Young Rabbits are a very important part of the diet.
- lack of males. For unknow reasons (illegal killing on the wintergrounds?) there are to less males when you compare the number with the females present.