Bird ringing in Britain and Ireland in 1999

Abstract

This is the 63rd annual report of the British Trust for Ornithology's Ringing Scheme presenting work carried out and data received in 1999. A study of long‐term trends in songbird productivity using constant effort ringing showed that changes have been markedly synchronised through time for some groups of ecologically similar species (eg resident insectivores, Blackbird and Song Thrush, Blue Tit and Great Tit). Significant decreases were found in the productivity (juvenile: adult ratio) of 15 of the 26 species, and no significant increases. For 14 species, higher temperatures over the summer months resulted in lower productivity, and greater total summer rainfall was associated with higher productivity for 11 species. Significant differences between regions of Britain & Ireland were detected for 11 species, highlighting the importance of maintaining sufficient numbers of monitoring sites to carry out analyses at the regional level. Comparison with nest record data showed that, for three species, the falling productivity may be a result of a decline in the number of nesting attempts or the immediate post‐fledging survival of young. Some changes in productivity were linked to changes in abundance; for others a density‐dependent negative change in productivity may have taken place and, for at least two species, changes in survival rates may be driving the observed population decline. Survival rates of adults of two declining species, Blackbird and Song Thrush, were measured using Constant Effort Sites (CES) data from 1983 to 1998. The annual survival of Blackbirds declined significantly and a strong relationship between annual survival rates and winter temperatures was found. A study of the declines in populations of Oystercatchers and Knot on the Wash found that winter survival rates of adult Oystercatchers have remained approximately constant (98%) from 1990 to 1998, except during three years of unusually low survival when both cockle and mussel stocks were low. Adult winter survival rates of Knot were more variable (70–97%). Indices of mussel and cockle stock size were significant in determining the over‐winter survival rate of Oystercatchers but did not influence those of Knot. An analysis of ring‐recovery and nest record data for Spotted Flycatcher showed that increasing mortality in the first year of life is likely to be responsible for the recent acceleration in the decline of this species. Data collected by the CES Scheme suggested that weather conditions during the 1999 breeding season resulted in mixed fortunes for Britain and Ireland's common songbirds. Adult numbers were significantly greater in 1999 than in 1998 for two species (Wren and Sedge Warbler) and significantly lower for three species (Chiffchaff, Willow Warbler and Blue Tit). Productivity (the percentage of juveniles in catches) was significantly lower for two species (Blackcap and Redpoll). 1999 was the second year of the Retrapping Adults for Survival (RAS) Project and 85 datasets covering 34 species were received. The number of birds ringed in 1999 (700,387) represents a 16% decrease from the five‐year mean 1994–1998. The recovery total (10,586) was 13% lower than the mean of the previous five years (1994–1998). Recoveries of 183 BTO‐ringed birds and 110 birds ringed abroad are presented in the report, including a number of significant movements of an unusual nature. Particularly noteworthy were two Storm Petrels found in Switzerland following a hurricane and a Pied Flycatcher ringed in the nest in Asian Russia (85° E) in late June and recaptured less than three months later in Yorkshire.