Last weekend Rob H. sent me a photo of a first-calendar year Black-headed Gull Chroicocephalus ridibundus that he had seen in Leiden. Bizarly, the photo showed an extra ‘foot’ on the tarsus of the left leg, complete with nails. Unfortunately the gull flew away before Rob could take a series of photos.
Today I came across the gull again in Leiden and was able to document this strange phenomemon in detail.
The video shows that the left leg seems to lack enough strength to fully support the gull, making it difficult to scratch its head with the right leg. Hopefully it’s able to do this while floating on the water so that he can get rid of any feather lice.