A case of polymelia in the Black-headed Gull Chroicocephalus ridibundus

Polymelia is a malformation consisting of the presence of supernumerary limbs. Although relatively common in farm animals and anurans, it is quite rare in wild vertebrates and, especially, birds. I describe here the case of a Black-headed Gull Chroicocephalus ridibundus seen in Barcelona (Catalonia, NE Spain) in January and February 2023 that had an atrophic leg originating from the distal posteromedial part of its right tibiotarsus. It was a healthy-looking bird, apparently in its second winter, and showed normal behaviour with no visible signs of any other pathology or malfunction. We are only aware of one previous case of polymelia in gulls and this is the first time it has been reported in a Black-headed Gull. It is also good example of survival in a bird affected by polymelia.