Grauwe Kiekendieven Circus pygargus in Nederland in 2005

In 2005, 39 pairs of Montagu’s Harriers were located in The Netherlands, i.e 30 in Groningen, 1 in Drenthe, 3 in Friesland and 5 in Flevoland (Fig. I). This indicates a stable population during the past decade, probably thanks to protection of nest sites in crops (only a handful of pairs nowadays breeds in semi-natural vegetation). Most nests were built in winter wheat (24 out of 38). As in previous years, many nonbreeding individuals were recorded, among which 9 males in their 2nd calender-year in Groningen (one of which carried a colour-ring, the first 2nd-cy male seen in The Netherlands and known to have hatched in The Netherlands). Bigamy was recorded in at least three males (none of which 2nd-cy) in Groningen, but as this phenomenon is difficult to reliably notice in harriers without radio tags, the proportion may have been higher. Overall mean laying date was 21 May (long-term average 1990-2004 = 24 May, Appendix 1), and noticeably earlier in Lauwersmeer (11 May) than in Flevoland (21 May) and Groningen (23 May). Mean clutch size averaged 3.3 eggs (Appendix 1). Slightly more than half of the nests (54%) was successful in raising at least one chick; Flevoland and Lauwersmeer showed better nest success than Groningen. On average, pairs produced 1.3 chicks/pair and 2.4 chicks per successful pair (Appendix 1). Compared with the long-term trend, these figures are average or less, reflecting a poor vole year. Pellets, prey remains and observations resulted in a prey list with 1155 items (Appendix 2), dominated in numbers (62,4%) and biomass (60,0%) by voles (Fig. 3). An increasing proportion of adult breeding birds carries a ring, including a colour-ring (in use since 1999). In 2005, 13 resightings and recaptures were registered on average 5.7 km from the ringing site (Table 1: 6 males and 7 females). Five male Montagu’s Harriers were fitted with radio-tags in order to collect data on habitat use and hunting efficiency. Two adult females were provided with a satellite transmitter, and were followed into Africa (Morocco and Niger respectively) until their signal faded (for details see www.grauwekiekendief.nl). In Jabuary 2006, a team of Dutch Monty aficionados travelled to Niger 2006 to study the winter ecology in the region where one of the tagged females had resided for some time.