First results of year-round tracking of Hen Harriers Circus cyaneus breeding in the agricultural landscape of East-Groningen

A small breeding population (3-5 pairs) of Hen Harriers recently established in the east of the province of Groningen, the Netherlands, in large scale arable farmland. We equipped three adults, two males and one female, with UvA-BiTS GPS loggers to study home ranges and habitat use throughout the year (Fig. 1). One breeding male could be tracked during two subsequent summers (late nestling phase in 2012, prebreeding and incubation phase in 2013 (Fig. 2)). Although he nested in the same area, he used different home ranges in these subsequent years (overlap only 21%). Habitat use was similar between years. Most time was spent in (winter) cereals (60%) and grassland (22%), two crops that dominate in the study area (availability is 42 and 24%, respectively). Moreover, set-aside habitats, which are especially created and managed for breeding harriers, were preferred (4% used, 1% available). One breeding pair was tracked after their nest failed (Fig. 4). These non-breeding birds occupied much smaller summer home ranges. In addition, they used set-aside habitat much more intensively (up to 22%), until the start of the cereal harvest when they switched to using cereal stubbles. During the summer the female made three subsequent trips to Northwest Germany (Fig. 3). One male spent the winter in Spain, in an agricultural area near Olivenza (Fig. 6). Autumn and spring migration took 98 and 14 days, including 81 and 1 stopover days, respectively. The other individuals (one male and one female) spent the winter near the breeding area (Fig. 5). Loggers could not record positions during mid-winter as solar panels could not keep the batteries charged. Habitat use in winter was dominated by grassland (62%). Set-aside was also preferred (5%). The female made an 8-day mid-winter excursion to a nearby wetland area (Weerribben, Fig. 5).