Feeding behaviour and diet composition of Marsh Harriers Circus aeruginosus in agricultural landscapes

Abstract

Capsule Diet composition and feeding behaviour of breeding birds differed between areas of high and low agricultural intensification. Aims To analyze diet composition and feeding behaviour of Marsh Harriers Circus aeruginosus in agricultural landscapes with different degrees of agricultural intensification. Methods Diet composition and feeding behaviour was assessed by focal observations at nests during breeding seasons in 2001-03 in two agricultural areas within the eastern Ebro Basin (on the northern Iberian Peninsula) which differed in their degree of agricultural intensification: a traditional non-irrigated and non-intensively managed farmland area; and an irrigated and intensively managed farmland area. Results Marsh Harriers in the intensively managed area took higher percentages of small mammals than harriers in the traditional area managed at low-intensity, where they also had a more diverse diet. Male delivery rates increased throughout the breeding season in the intensively managed area. On the contrary, no significant trend in delivery rates was observed in the traditional area, where harriers turned to larger prey late in the season. Conclusion Marsh Harriers probably took advantage of different prey types in intensively managed and traditional farmland according to prey availability. Differences in diet composition seem to be related to different foraging strategies adopted by harriers in traditional and intensively managed farmlands. In the traditionally managed farmlands, harriers responded to increases in the energy requirements of the brood over the course of the breeding season by taking larger prey, whereas in the intensively managed farmlands harriers increased feeding rates. © 2012 British Trust for Ornithology.