Like so many of Dorset's special birds the short-eared owl (Asio flammeus) breeds in northern regions and comes to us for the winter months. In Britain they nest mainly, but not exclusively, in upland moorland regions of northern England and Scotland but they also breed throughout northern Europe as far south as France. The more northerly areas are not suitable for them in winter so they migrate south and a small number turn up in Dorset every year but the numbers vary depending on the severity of the weather further north and the abundance of suitable prey available to them.
The weekly reports chart shows a small number of records of short-eared owl during the summer months but it is week 42 in mid-October that the reports start to increase and then there are frequent reports right through the winter until week 10 in mid-March and a few remaining reports come in until week 16 at the end of April by which time they have returned to their breeding grounds.
Portland produces by far the most records for short-eared owl with three of four birds usually over-wintering there each year and they are often quite visible being seen hunting by day. There were reports from twenty five other sites during 2017/8 but just odd sightings and nothing quite as regular as on Portland and it does seem that many of the Dorset sightings are birds on the move south, or returning north, rather than those staying with us for any length of time.
Experience would suggest that the upper reaches of the fields at Portland Bill in mid-winter around dusk is your best chance of seeing short-eared owl in Dorset.