Vegetation height selection in Montagu’s Harriers Circus pygargus breeding in a natural habitat

Abstract

The selection of an appropriate site for nesting is of vital importance in birds, especially in ground nesting species as Montagu’s Harrier Circus pygargus. This raptor mainly uses cereal crops as nesting habitat, although natural vegetation is also used in some European areas. Vegetation height is one of the main factors affecting nest location in cereal crops but there is no data on its importance in natural habitats. In Castellon province (NE Spain), the species uses shrublands as breeding habitat, which provides the opportunity to explore the importance of vegetation height in birds breeding in natural areas. In this study, we compared vegetation height at nests with vegetation height in the surrounding of the nests, and at random points within patches occupied by harriers. Mean vegetation height at nests was 83.5 cm (SD 17.2), which corresponds to observations in other natural vegetation sites and cereal crops. At one metre from nests, the vegetation was higher, with a mean value of 109 cm (SD 16.0). Mean vegetation height at random points was also 109 cm. This contrasts with observations in cereal crops, where nests are located in sites where vegetation height is equal or higher than the surrounding vegetation. In our study area vegetation height seems to play an important role in determining the exact location of nests within a patch, but in terms of vegetation height the areas used by harriers for nesting do not differ from the rest of the patch. This suggests that most sectors of the patches are potentially suitable for nesting, with the selection of shorter vegetation for the exact location of the nest probably resulting of a trade-off between nest protection and nest accessibility. As populations breeding in cereals need human intervention to be sustainable, and in the absence of conservation measures breeding output is higher in natural habitat than in farmland, the protection of populations inhabiting natural habitats may be important for the conservation of the species in a wider context, as they may act as sources of harriers for other areas.