VERVOORT MPJ & KLAASSEN RHG (2016) Foraging behaviour of wintering Hen Harriers Circus cyaneus in Eastern Groningen. LIMOSA 89 (4): 145-153.

Recently, a small breeding population of Hen Harriers established itself in the intensively-farmed agricultural landscape of Eastern Groningen, possibly as a result of agrienvironment schemes (set-aside habitat) implemented for Montagu’s Harriers Circus pygargus. A few breeding Hen Harriers equipped with GPS-loggers revealed that in winter the birds predominantly forage over grassland instead of set-aside, despite the fact that set-aside generally harbours higher densities of voles, the harriers’ main prey in the study area in winter. In order to explain this paradox, in September November 2015 we studied foraging success of harriers hunting above grassland and set-aside. Harriers more frequently attempted to capture prey (more encounters and strikes per hour hunting time) on set-aside compared to grassland. However, the number of prey captured per hour hunting time was similar across habitats. Indeed, strike success was lower for set-aside compared to grassland. We conclude that because prey are more difficult to capture on set-aside, presumably due to a more complex vegetation structure, grassland is a favourable alternative foraging habitat. Thus, not prey abundance per se but prey availability dictates foraging habitat selection. An interesting new concept in this respect are so-called bird fields where strips of set-aside (aimed at boosting vole numbers) are combined with strips of alfalfa (to make voles available after harvest).

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