I think there are many reasons. This area, Brandenburg, looses more and more wetlands. Instead there is more intensive farming.
You find strawberry fields covered with plastic, asparagus fields, covered with plastic, and lot of former wet meadows are now used for corn and other energy plants. The storks do not find enough food.
And we have the clima change. This area is very dry now and there is not enough rain anymore. This is also a reason that the storks do not find enough food.
My fingers are also crossed for a breeding stork couple next year.
Here you find a list of all European stork cams.http://storchencam.eu/