The hen harrier is a specialist of moorland habitats in northern Britain and so the heathland in the Poole basin makes a good wintering alternative location and a small number of these magnificent birds can be seen here outside of the breeding season. Sadly they are a much persecuted species in their breeding areas where they are perceived to be a threat to commercial grouse shooting and so numbers in Britain are now very low and consequently the numbers in Dorset in winter are inevitably low as well.
Hen harriers start to be reported in Dorset during late August from week 33 onwards but the number of reports starts to pick up from week 40 in October. This might imply that earlier sightings are birds intent on moving further south and are just passing through whereas the October birds are possibly staying long term. Reports are fairly consistent right through the winter until week 7 in late February and then they start to tail off. By week 16 at the end of April they are all but gone and are back in their nesting territories.
The distribution map shows that the various sites around Poole Harbour are a popular place with hen harriers being seen in the harbour over reed beds and also on the adjacent heathland. There are reports from along the Dorset coast as well, especially along the Fleet, and these are possibly more likely to me migrant birds leaving or arriving whereas the Poole Harbour birds are more likely to be long staying.
Finding hen harriers in Dorset is a little unpredictable but if there are wintering birds in the area then the hide at MIddlebere Farm is as good a place to lie in wait as any.