Comparative breeding biology of Hen Harrier and Montagu's Harrier: an 8-year study in north-eastern France

Hen and Montagu's Harriers breed in the same cultivated areas of eastern France. We present data from an extensive study conducted in three adjacent areas where 757 nests of the two harriers were monitored between 1993 and 2000, with the aim of comparing the breeding ecology of these two species and to evaluate their possible future trends. Breeding habitat for harriers consisted nearly exclusively of winter cereals, causing great conservation concern in this intensively farmed region. The Hen Harrier was almost absent from two of the study areas. This species showed significantly larger clutch size and higher breeding success than the Montagu's Harrier, and an earlier breeding phenology. It was thus less adversely affected by harvesting activities than Montagu's Harrier. Both species showed a reduced breeding success with increasing laying date. There was a large diet overlap between the two species, possibly leading to competitive interactions. Overall, the Montagu's Harrier should be considered as the more vulnerable of the two species, necessitating conservation measures, such as protection of nests from early harvesting activities. Nevertheless, to maintain both species in agricultural habitats, farming practices that preserve sufficient food should also be promoted.