Insects in the diet of urban kestrels from central Europe: An alternative prey or constant component of the diet?

Abstract

During the years 1996-1998, the diet composition was assessed from pellets of kestrels in České Budějovice. Within the total number of 5226 prey individuals, insects made up 15.2% by numbers and 0.3% by weight. In the summer and early autumn, the abundance of insects was highest. It was partially caused by including pellets from juvenile kestrels that contained more insect remains than pellets from adults in general. Two main insect groups were found in the diet - beetles (mostly medium-sized Carabidae) and Ensifera (large Tettigoniidae). In the low vole year, the intake of beetles was higher in comparison with high vole year, whereas the intake of Ensifera was rather stable in both years. Our results support the "alternative" role of beetles in the diet of kestrels. However, the beetles are energetically incomparable with voles and are partially at least caught during the hunting on voles. Ensifera were more likely hunted with purpose. Contrary to beetles their proportion at individual roosting sites was balanced.