One of the most striking things about the Hen Harrier is that the male and female differ remarkably in size and colour. Adult males are a pale grey colour, females and immature birds are brown with a white rump and a long, barred tail. Females and immature birds are hard to tell apart and are collectively called 'ringtails'. Hen Harrier also have a distinctive flight, with wings held in a shallow 'V', usually seen gliding low in search of food.
There are many aspects of the Hen Harriers' life history and behaviour that make it an extraordinary and alluring species.
To claim territory and a mate in Spring (around March and April), male Harriers engage in spectacular courtship displays (the sky dance). Males fly very high into the sky, then free fall, spinning and somersaulting. Sky dances are an effort on behalf of the male to advertise his prowess, skill, strength, agility and stamina to potential mates.
The Hen Harrier is a ground nesting bird adapted to open moorland and marginal grassland habitats. The traditional nesting habitat of Hen Harrier across Britain and Ireland has been predominantly Heather. When the pair forms, they chose their location very carefully. Nest site selection for birds is chiefly associated with safety, shelter and proximity to food resources.
Another amazing and spectacular trait of the Hen Harrier is the food pass. The male, carrying prey in his talons will call to the female as he approaches the nest area. The female will rise to meet the male and as she comes near him, will somersault upside down, and the food is passed from his talons to hers in mid-air.
Outside the breeding season Hen Harriers gather at communal roost sites at night. Hen Harrier roost sites can be communal (frequently used by several individuals) or solitary (used by individual birds regularly and/or infrequently. Roosts are used as safe bases from which to radiate out to hunt the surrounding landscape during the daytime. Hen Harrier select sites with suitable cover, low ambient levels of disturbance and presumably close to suitable foraging areas to roost.
The national Hen Harrier population has been declining for the last 40 years with only an estimated 108 – 157 pairs remaining. Within the SPA network the breeding population of Hen Harrier has declined by 27% since 2005.The semi-natural habitats that the Hen Harrier depends on have decreased in area as demographic, economic and regulatory factors have driven changes in land use.