SCHLAICH A & KLAASSEN R (2019) Ecology of Montagu's Harriers Circus pygargus wintering in the Sahel revealed by a combination of high-tech GPS-tracking and old-fashioned fieldwork. LIMOSA 92 (3): 175-183.

Population regulation in migratory birds is complex as they depend on several widely separated areas. Often relatively little information is available from the wintering grounds, despite the fact that migrants yearly spend up to half a year at their wintering quarters. Here we provide an update on the knowledge on the ecology of Montagu's Harriers wintering in the Sahel, building on analyses of GPS-logger and satellite tracking data, and old-fashioned fieldwork in Senegal. We show that Montagu’s Harriers use on average three different sites during the winter, in which the timing of the movement to the subsequent site is determined by local conditions; in dryer years birds move earlier. At the last wintering site the birds are faced with deteriorating conditions as the Sahel continues to dry out. Harriers compensate by flying more hours per day. Previous studies showed that relatively few birds die during the winter period. However, new data indicate that mortality rates have doubled, suggesting that the winter period has become a more challenging period in the harriers' annual cycle.

[pdf only for members] [dutch summary]