As part of its Garden BirdWatch survey, the British Trust for Ornithology (BTO) has been collecting records and photographs of birds with beak deformities. To date they have reports relating to 32 species and the suggestion, surprising given that this is a garden bird survey, is that Rooks are the birds most likely to be affected. Blue Tits and Blackbirds are also high on the list.
Several different kinds of deformity have been recorded and there are apparent differences between species as to how they are most frequently afflicted. A Blackbird, for instance, is more likely than most to have an overgrown lower mandible, while an overgrown upper mandible is the most common deformity in Blue Tits.
Similar research by the U.S. Geological Survey (USGS) has been in progress in Alaska since 1999. There, more than 2,000 deformed Black-capped Chickadees have been identified, claimed to be the highest concentration of such abnormalities ever recorded in a wild bird population anywhere. More recently, rapidly increasing numbers of other species in Alaska, including Northwestern Crows, Downy Woodpeckers, Steller’s Jays and Black-billed Magpies have also been reported with beak deformities.
There are no firm conclusions yet about the causes of these deformities but contaminants (industrial pollutants, insecticides, herbicides and fungicides), nutritional deficiencies, disease, parasites and genetic abnormalities are all on the list of suspects.
Our interest in this research was sparked by these two gulls that we saw yesterday at Olhão.
For more information about the BTO research and the consequences and odd behaviours resulting from beak deformities, go to their website. You can follow links from there to read about the USGS research.
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