The Sedge Warbler in Dorset

Whilst the sedge warbler (Acrocephalus schoenobaenus) is a summer breeding visitor to Dorset a significant number of the reports of this species are of those on passage to elsewhere in Britain to breed. As with many summer migrants they arrive over a short period of time generating a peak in reports but the outward journey is spread over a much longer period and so it becomes less obvious to detect from the number of reports. The names of most, not all, warblers are fairly descriptive of their preferred habitat or of their appearance and this is so with the sedge warbler as they nest in deep sedge or reed beds and as Dorset has a number of reed beds the sedge warbler is not uncommon in the locations where suitable habitat exists. Birds seen elsewhere will, in general, be passage migrants.

The Twitter reports would suggest that the sedge warbler arrivals begin quite early in spring in week 12 in late March but the peak for arrivals is between weeks 16 and 19 in April. By early May they are back on their patch and singing in territories and this is when they are most evident as a breeding species. Once their chicks hatch the singing stops and the frantic feeding of young deep in the reed bed starts and so reports tail off and so there are few records between week 23 and week 28 in June and July. Autumn migration south to Africa seems to start around week 29 and continues with the latest report we have being in week 39 in late September but most seem to go in August.

There are records from thirty nine sites in Dorset and the bulk are from river, lake or harbour locations where there are reedbeds; not always large reed beds but size does not seem to be a criteria for the sedge warbler. Given there are few, if any, reed beds on Portland it may seem surprising that Portland produces the most records but it seems Portland is a popular landing point for incoming birds and many are ringed at Portland Bird Observatory each year.

Ticking off sedge warbler on your Dorset list should be quite easy if you visit any reed bed in May where you will hear the sedge warbler's grating song coming from within the reeds.