BOEDELTJE G & ZIJLSTRA, M (1981) Territoriality, habitat and prey of wintering Hen Harriers Circus cyaneus. LIMOSA 54 (3): 73-80.

This paper describes the hunting habitat and hunting behaviour of the Hen Harrier Circus cyaneus in Flevoland (fig. 1) during the winters of 1976/77 and 1977/78. The main results are:
(1) The total number of wintering Hen Harriers was the largest in the beginning of February; adult males formed a small minority (fig. 2).
(2) Hen Harriers mostly hunted in extensively managed, trenched hayfields. Reeds and recent afforestation were also important as hunting habitat. There were hardly any Hen Harriers in arable areas (fig. 3).
(3) Adult males prefered hunting in vegetations that were little structured (especially grasslands), the other birds however also often hunted in reeds, recent afforestation and rough vegetations (fig. 3).
(4) The main part of the pellets consisted of Microtus arvalis (86%) and Passeriformes (6%) (tab. 2).
(5) In areas where Hen Harriers more often hunted in reeds and recent afforestation, less Common Voles Microtus arvalis occurred in pellets than in areas where they mainly hunted in grasslands (fig. 4).
(6) Eight female coloured Hen Harriers, individually recognizable, defended a hunting territory. The territorial behaviour hitherto unknown in wintering Hen Harriers is described (fig. 5).
(7) Adult males are not sighted defending a winter territory. The average size of a hunting territory was 35.5 ha in one area and 8.0 ha in an other one (tab. 3). This difference is supposed to be related with the density of Microtus arvalis (tab. 1).
(8) In the area with the largest territories less conflicts with conspecifics were recorded than in the area with small territories (tab. 3).
(9) The hunting success of the Hen Harrier averaged 8.1% (for adult males 12.0%; tab. 4). The hunting yield (the number of voles caught per hour of hunting) averaged 1.40, that of the adult males 1.56.
(10) Daily food intake was on average 10.5 voles (cf. Microtus arvalis in tab. 5). If the average weight of Microtus arvalis is put at 16.8 g (after catches in the winter 1976/77), the daily food-intake amounted to c. 176 g of Microtus arvalis. Since the prey is not eaten completely, the real quantity will be less.
(11) A female coloured Hen Harrier spended about 27.8% of the available time for hunting (25.5% flight hunt, 2.3% ground hunt) (tab. 6). Hen Harrier Circus cyaneus

[free pdf] [dutch summary]