Foraging strategy in the spoonbill (Platalea leucorodia)

The aim of this study was to find factors that made the spoonbill colony in the Zwanenwater decrease so drastically. Three to four hundred pairs of the spoonbill Platalea leucorodia bred in the Zwanenwater around 1930 against 60 pairs in the last years. Foodintake rate is determined in five different areas of the spoonbill in the north of the province of Noordholland. Five different types of prey can be distinguished with different weight and density. This study shows that weight of prey is much more important for high foodintake rate than density of prey. The stickleback is the most important prey for the spoonbill of the Zwanenwater. There is much variation in size between fish of different stickleback populations. The areas with populations with big sticklebacks are the ones that are visited most by the spoonbill (Wieringerwaard). The exclusion of migrating 3-spined sticklebacks from the polders might have caused the decline in number of spoonbills in the last fifty years.