Territorial singing during the summer gives way to a period of relative quiet in late July and early August, after which they start up again and sing through the year. I have also noticed occasional aggression between neighbouring males during the winter. Territory is fundamental to breeding success - they don't sing for fun, and as the males I find here in the winter can sometimes stay to breed in the same territory, it is easy to see why they want to keep hold of their ground. If your Trog trogs are migrating away to breed, then it is less obvious why they need to sing, but if they are singing then they are certainly holding a territory. Winter survival for these guys is dependent on intimate knowledge of a patch of ground, with associated undergrowth in which they can find shelter and food.
Females seem to be oblivious of the territory boundaries in winter.
I agree with Norman van Swelm that the bird in the photo is a Lesser. There is much individual variation. I would add that it may be tough to judge what the final pattern will be on a 2nd-generation scapular while it is still growing. The diffuse appearance and blunt shape of the indicated feather suggest that it might have a bit of growing to do yet. There is much individual variation.