Swallow in Aberdeen (1 Viewer)

Posted this elsewhere but maybe better here. Work at hospital in aberdeen and have watched a pair raise 2 broods this year (outside kitchen window). About a week ago they all left apart from 1 bird (dont know if its an adult or youngster) Where they nested is undercover and reasonably warm but why would it be left? seems to go out during the day and come back to roost, but its very cold here now (snow yesterday) so what will it be finding to eat? Anyone shed any light for me? can i somehow leave food for it (thinking not)

Bird was roosting in its usual spot last night and left for i presume foraging at about 7.45am

I wonder what's the latest a Swallow has been reported in Aberdeen, it does seem awfully late for this cold weather, doesn't it.

Now... I wonder how long it'll stay?