Its possible they were part of a larger roost. There is a very large roost near Hopwood College, Middleton. It has been there for a number of years now and tends to move around from Glade Wood to Oaken Bank Wood. It consists of over a thousand birds, mainly Jackdaw and Crow but with some Rook. The numbers were estimated a few years ago by another birder who posts on this site (Bill Myerscough). He reakoned that there were groups of 150 to 400 birds at a time joining it on a day he was watching. Check the thread for 'Hopwood Woods LNR' from around 2012. Its one of my favourite sights at this time of year. I tend to watch it from 'dead mans hill' in Lord Wood just behind the lake. I've noticed lots of birds coming in from the east Oldham area.
I'm relatively new on the forum but rapidly learning its value.
Does anyone keep track of corvid roosts over winter?
I ask because I've been following Jackdaws that roost from the East Oldham area. So far I've tracked them down to what I thought was a roost near to Fitton Hill/Park Bridge, Oldham. I've visited the 'roost' for about three weeks and watched about 600 mainly Jackdaws settle in trees there. Today though I visited on the first day when it has not been a clear sky with a lovely sunset, it was overcast. No Jackdaws came only a small group of Carrion Crows.
I'd be interested in whether you think that the 'roost' I've been watching is actually part of a much larger roost and I've simply missed this large group moving on, or whether some other reason prevented them coming today. There were certainly no travelling birds on my return home which would suggest they had already gone to roost somewhere.
