Bue tit on my bird feeder

This was quite early today as I was watching the Sunday morning re-run of Match of the Day, a programme much loved by all football loving insomniacs. All of a sudden the feeder was visited by a flurry of these non-sparrows, alighting, sometimes three at a time from adjacent bushes. They seemd puzzled that the seeds were not accessible through the perspex. I got the impression that they were just passing through. What's happened to that blasted window cleaner?