Roosting Skylarks

As the cold weather begins to bite, I cannot help wondering how ground roosting birds cope with the cold. There are still plenty of skylarks feeding on the stubble and as they are here late into the day, it seems clear that they roost in situ. I have seen flocks of twenty or more. I presume that they group together to benefit from the body heat generated by each individual bird. But, do they then, as some other roosting birds have been seen to do, move around so that the birds on the outside of the group get a turn within the heated space?
In the distant past, this roosting behaviour was what led to their downfall. For, when the birds were commonly kept as cage birds, the trappers would drag a net across an open field during the hours of darkness. No doubt they first observed the birds to see where they roosted. On hearing the weighted back of the net scrape along the ground, the birds would rise into the air and get caught. As they roosted in groups, quite a number of birds could be caught in a single drag.
It is interesting to note how disputational the skylarks can be. Fiercely territorial during the breeding season, you might anticipate that they would become placid in the winter, but in their loose flocks , they seem to be forever involved in minor skirmishes with other birds.