Oliver P.J. (2005) Roosting behaviour and wintering of Eurasian Marsh Harriers Circus aeruginosus in south-east England. ARDEA 93 (1): 137-140

Eurasian Marsh Harriers Circus aeruginosus used roosting sites in tidal salt marshes and a reed-filled fleet for 13-15 winters, other sites in reed and crops occasionally. Most wintering birds were female, with males consistently accounting for 10% of winter totals (but doubling from 2003/04). Pre-roost gatherings, including group-circling, were typical. The increase in wintering numbers paralleled a similar trend in local breeding numbers, as also recorded in The Netherlands and Belgium. This indicates that local conditions are probably not the driving force behind the increase.