It doesn't fit the bill

While photographing the new crop of young birds in the garden I noticed this woodpecker on a feeder.  His lower mandible is elongated and decurved.  His plumage looks OK but perhaps lacking in preening.  I haven't seen him before and I don't usually see woodpeckers on this feeder - they prefer peanuts or suet and fat in the log feeders.  It is is difficult to see how he survives - he presumably can't feed like a normal woodpecker, either from hunting for grubs under bark or from a peanut feeder.

I have reported the sighting to the BTO Big Garden Beak Watch.  Running since 2010 (I think), the survey collects information on beak deformities in all British birds

I previously reported the crossed-bill deformity in this stock dove which at the time was the only one the BTO had come across, although affected woodpigeons and collared doves have been seen.  The pictures were taken on a trail camera.

I also reported this blue tit which had a crossed-bill deformity plus very obvious feather abnormalities.  It was puffed up and lethargic and presumably didn't survive long.  It would be a reasonable guess that the abnormalities are connected in some way as both feathers and beaks are made of β-keratins.

More than three quarters of birds with beak deformities in the BTO results had normal plumage - which is odd when you might think they would have difficulty preening and looking after their feathers.  Only 6% appeared ill with lethargy and fluffed up feathers like my blue tit.  Raw data from the BTO survey showed that blue tits, blackbirds, starlings and great tits were most commonly affected.  When corrected for frequency of reporting the birds most commonly affected by beak disorders were rooks, blue tits, blackbirds and pheasants (my pheasant is OK I'm pleased to say).

The cause of most beak deformities is not known.  They are not seen in birds less than six months old.  Probably only a few result from injuries such as collision with a window while genetic abnormalities, exposure to toxic substances, nutritional deficiencies or a combination of factors have all been suggested without any real evidence for each.  The BTO are comparing their findings with research from Alaska where beak deformities seem particularly common in black-capped chickadees (1 in 15) and north-western crows(1 in 6!).