more Firecrest on the patch

upper two shots Andy's bird from yesterday and the rest the bird I came across in a different area this afternoon; I am convinced they are different birds, both singing males, but today;s bird had much more buff colour on the chin and throat and a less white super BUT the main thing that struck me was its unusual song addition -- on about 50% of the occasions when it sang it preceded the song trill with a very distinct tseeeuuu note that it sometimes also added to the end of the song; I have never heard this before from a Firecrest but it was usually associated with the raised crest ( no playback going on) and suggested aggression but there were no other Firecrests about that I could ascertain although there was a singing Chiffchaff nearby