During an evening search for ringed Sooty Terns in the Bird Island colony on 8 June, the youngest member of our team, Dylan Savy, found an incubating adult with its tongue extending below the lower mandible, having pierced the skin and other tissues in the bottom of the mouth. This condition is called a sub-lingual fistula. This is the first time that we have seen it on Bird Island, despite the handling of tens of thousands of Sooty Terns here over the past almost 50 years.
It has been found very rarely in birds. First reported in a New Zealand Stitchbird (local name Hihi), the condition has subsequently been recorded in a Masked Booby on Ascension Island (south Atlantic) and in some adult Sooty Terns, also on Ascension.
Neither the cause of the condition, nor its effect on the feeding abilities of the affected birds, are known. Any reports of this condition in any species are requested by Jim Reynolds, University of Birmingham, UK (https://ornithologyexchange.org/forums/topic/29310-seeking-records-of-birds-with-bill-abnormality/)