The bar-tailed godwit is far less common in Dorset than its black-tailed cousin. This may be partly due to lack of recording due to difficulties some less experienced birders may have in identifying them as the two species are superficially similar but, despite this, there are far, far less bar-tailed than black-tailed godwits seen here. The bar-tailed godwit is, apparently, much more common further north in Britain with less coming down to the south coast from their breeding grounds in the Arctic regions of Scandinavia and Siberia.
Some bar-tailed godwit migrate to the coastal waters of southern and western Europe and some go as far as north Africa. This may be reflected in the weekly reports chart which shows a pronounced spike during weeks 16 to 20 in April and there also seems to be higher level of reports from week 35 to 40 around September time. Outside of these peaks the reports show that you can see bar-tailed godwit at any time of year with not only birds wintering here but a very small number of non-breeding birds staying for the summer too.
This species has a slight preference for more sandy areas exposed at low tide and Ferrybridge and Sandbanks are good places to find them but any tidal region with mudflats also provides reports, especially during the two migration periods. With this in mind all of the Poole harbour sites and those along the Fleet are likely to yield bar-tailed godwit at some point.
If you are looking for bar-tailed godwit for your list first learn the differences between it and the black-tailed godwit and then keep an eye on the news to see where and when the most reports are coming from.