Great Tit Bill Deformity

This morning I had things to do around the house and so opened a net in the garden. The session was ticking along steadily with mainly blue and great tits, a couple of nuthatches and a goldfinch, and then I caught this...

Adult Male Great Tit with Extra Long Upper Mandible

I have caught birds with deformed bills before, and in fact have posted on this blog images of a blue tit with a deformed and crossed over bill, but this bird was amazing. The upper mandible measured an amazing 28.5mm, greatly overlapping the lower mandible, which also appeared longer than the norm. 

Long Billed Adult Male Great Tit

Given the extent of the overlap, it was difficult to image how this bird could successfully feed, and unfortunately it turned up in the net before I saw it trying. However, it had clearly adapted to its deformity, since the bird was an adult, had a fat score of 1, a muscle score of 2 and a very healthy weight of 20.4 grams. Out of interest this weight was the heaviest of the four great tits I have trapped by 2.3 grams.

Under side of Long Billed Adult Great Tit

The British Trust for Ornithology are currently carrying out a Garden Beak Watch Survey the link to which is here. There are several suggestions as to why beak deformities occur in birds, on their website the BTO state that they "could be influenced by disease or may be inherited genetically and while research continues to investigate these possibilities, current evidence is not comprehensive". Whatever the cause the result, as in this bird, can be quite spectacular and you can only admire how the individual has adapted to survive with its deformity.