Guillemot (Uria aalge) Science Article 1
When ashore, a Guillemot Uria aalge usually walks with the tarsus in contact with the ground and this results in severe wear of rings. Even the change from soft to hard metal rings in the early 1960s only increased the useful life of a ring placed on a Guillemot to around 10 years, after which the ring numbers still became illegible if the ring had turned or had been put on upside down. During the early 1980s the British Trust for Ornithology (BTO) developed a special ring for use on Guillemots in an attempt to reduce the adverse effects of wear on the longevity and legibility of rings. […].
M. P. Harris and P. Rothery, Ringing & Migration (2004) 22, 61-62