Crossbill, Avocet or Wrybill?

Beak deformities in wild birds are unusual, with fewer than one in 200 adult birds thought to be affected. As long as the bird can feed and preen once a bill is deformed enough that the tip isn't constantly worn away, it can grow to amazing lengths.

Juvenile Blue Tit with the a bill deformity. Ipsley Alders Nature Reserve, Mike Barstow

Whilst ringing at Ipsley Alders Nature Reserve, Redditch, Mike Barstow retrapped a Blue Tit on 25/11/2013 that he previously ringed on 19/01/2012 with no deformity noted. This bird now had a severely deformed bill (below). The bird appeared healthy with good plumage, muscle and even had a trace of fat. There are therefore two birds (above and below) that have been recorded at this site which have developed a beak deformity within a few years.The research continues.

Adult Blue Tit. Ipsley Alders Nature Reserve, Mike Barstow

Measuring bill length to investigate growth rate for future captures- Mike Barstow

 Types of beak deformities in the wild:

• Crossed mandibles: similar to that of a Common Crossbill perhaps caused by slight asymmetry of the jaw. Straight beaks have been recorded as a deformity in Crossbills.

• Decurved upper mandible: can occur when the tip of the lower mandible is damaged so that the beak does not close correctly.

• Upcurved lower mandible: may occur when the tip of the upper mandible is missing (i.e. broken off).

• Elongation of both mandibles: produces ‘Curlew-type’ beaks, although the degree of curvature varies considerably between individuals.

• Bent to the side: seemingly uncommon, with one or other mandible warping sideways.

• Gapped: where the upper and lower mandibles do not close fully leaving a visible gap.

For more information click here

Another Curlew Tit is spotted

The life of a wild bird is not an easy one. The BTO get quite a few reports of 'unusual' looking birds with abnormal plumages and deformities. The types of deformity vary widely but the most commonly reported are of the legs and especially the beak.

The most common bill deformities reported by Garden BirdWatch members are:

• Upper mandible over grown
• Upper and lower mandible crossed over
• Upper and lower mandible elongated together
  
• Lower mandible over grown
• Bill fractured
  

Ringers are in the unique position of being able to record abnormalities by measuring and by taking photographs. John Griffin from Devon recently caught this adult Blue Tit with an 18mm long bill! The cause behind this abnormality is unknown but this bird was at a healthy weight so was able to feed and take care of its plumage to some extent.


Ringers have reported ringing birds (Blue Tits in particular) with normal beaks and then, on re-catching these birds again months later, they have varying abnormalities. This proves that the abnormalities in birds can occur at any time in their lives. The most common bill deformities in Blackbirds are fractured bills, however this is rarely reported in Blue Tit, Great Tit or Starling. More information can be found on the Garden Birdwatch pages.

Thanks to John Griffin for letting us know and the photo.