Hen Harriers (Circus cyaneus) are highly mobile raptors that exhibit distinct wintering behaviour, often forming communal roosts in open landscapes such as moorlands, coastal marshes, and lowland heaths. In contrast to their territorial breeding behaviour, wintering Hen Harriers may gather in loose groups at traditional roost sites, where they seek shelter from harsh weather and reduce predation risk through collective vigilance. In England, roosting typically occurs in areas with dense vegetation, such as reedbeds, rush pastures, or heather moorland, which provide both concealment and protection from the elements. Birds generally arrive at the roost around dusk and depart at dawn, with timing influenced by weather conditions and daylight length. 

Estimates of the number of non-breeding Hen Harriers in England based on data from systematic surveys in the 1980s and 1990s give a broad range of approximately 200 to 700 individuals. Hen Harriers are listed under Section 41 of the Natural Environment and Rural Communities Act 2006 (Species of principal importance for conserving biodiversity in England) and are currently Red-listed by the UK Birds of Conservation Concern due to historic and ongoing persecution, particularly on their upland breeding grounds. 

As communal roosting makes them more conspicuous, concerns persist that these sites are particularly vulnerable to persecution and habitat loss. There are currently 13 Special Protection Areas (SPAs) in England where non-breeding Hen Harrier is a classified feature. Only two SPAs in England are classified for breeding Hen Harriers: the Forest of Bowland and the North Pennines. In contrast, the other UK SPAs for Hen Harrier comprise 12 sites (10 in Scotland and two in Wales) for breeding Hen Harriers and just four (all in Scotland) for non-breeding Hen Harriers.

There are two main sources of data where information on Hen Harrier distribution in winter can be obtained: the Hen Harrier Winter Roost Survey, which is a dedicated survey focusing on traditional roost locations in England, and BirdTrack, which is a general repository for records submitted by members of the public.