Wear and loss of rings used on Razorbills Alca torda – further caution in the estimation of large auk survival

Abstract

On Græsholmen in the central Baltic Sea, 3,583 Razorbill Alca torda chicks were ringed with triangular Incoloy rings, and about half the birds were subsequently resighted. The resightings were used to calculate rates of turned rings, and 119 retrieved rings were used to calculate rates of wear and ring loss. At 1.7%, the rate of turned rings was much lower than reported among Common Guillemots Uria aalge in Britain, most likely because the Razorbill rings were fitted with soft wax at the time of ringing. The mean annual rate of metal loss of rings on birds for 3–9 years was 1.51%. Ring loss due to abrasion was 50% by year 14 with no ring lasting longer than 24 years, thus severely biasing survival estimations based on ringing data.