The woodlark is considered to be a resident species in south west England but its scarcity in Dorset in winter indicates that our breeding population is inclined to move further west in cold weather or some may head across the Channel into Europe. There does not appear to be any noticeable passage migration at specific times of the year here. As a breeding species it is most likely to be encountered on heathland featuring scattered areas of open woodland, usually conifers such as Scots pine. It is a ground feeding bird eating seeds in autumn and winter but insects in spring and summer. It is an early breeding species with nests containing eggs found as early as March in some years and pairs often have two or three broods during the breeding season.
The tweeted reports in the Nature of Dorset database indicate a general absence of woodlark between week 48 at the end of November and week 2 in mid January but from week 3 onwards reports are more frequent as birds begin to take up territories prior to nesting. There are a good number of reports throughout the spring until week 27 in early July and then there seems to be a break with just the odd record until week 40 in October. Where the woodlarks go during this time in late summer is not clear, maybe they are just harder find during this period, possibly because of the moult? Occasional records during this time might indicate that the woodlark is here but elusive during this period.
Forty three sites have records of woodlark with about a half having just the one record which might indicate that those sites do not have a breeding population but have seen winter dispersed birds. The bulk of the sites are from the Purbeck and east Dorset heathlands which are known as a stronghold for the species. Other records are from further west and coastal so that might indicate some migrational movement. Arne and Wareham Forest, especially around Morden Bog, are good sites for woodlark.
The best chance of woodlark for your Dorset list would seem to be the newly opened Hyde Heath Trail at Arne, possibly in spring or autumn.