Bird ringing in Britain and Ireland in 1998

Abstract

This is the 62nd annual report of the British Trust for Ornithology's Ringing Scheme, presenting research carried out and data received in 1998. A study offish‐eating birds, initiated because of a perceived increase of predation on fish populations in inland waterbodies, established that there has been an increase in the proportion of ringed Cormorants that are found inland and that this increase took place before the increase in continental Cormorant populations or the establishment of inland‐breeding in Britain. The rise was coincident with the main period of stocking of inland waterbodies for angling. In addition it was established that birds found in each inland area were from a variety of breeding sites, so control at a particular breeding site will not be effective at controlling predation levels at a particular water body. A major project on habitat fragmentation and woodland birds, which particularly investigated the role of dispersal, was completed. Recovery data were used to calculate mean natal (away from the nest) and breeding (away from the breeding area) dispersal distances for 75 terrestrial species. In addition, recovery data were used to estimate survival rates used in studies of density dependence and to examine the influences of reproduction, mortality and dispersal on the size of bird populations. Research on farmland seed‐eaters suggested that changes in survival, probably as a result of changing agricultural practices, are likely to have led to changes in population trend for Goldfinch and House Sparrow. A study of Reed Buntings showed that population declines have been largely driven by declines in survival rates; the study suggested that this may be the result of decreases in the availability of grass and weed seeds on farmland in winter. Continuing studies of Song Thrush led to the development of a method for analysing survival not just in terms of adult and first‐year survival but splitting the first year of life into the immediate post‐fledging period and the rest of the first year so that the part of the life cycle where survival rates are changing can be defined more clearly. Fieldwork for the Retrapping Adults for Survival Project began. This project will gather survival information on a wide range of species in Britain and Ireland using targeted trapping for specific species for mark‐recapture analysis. By the end of 1998 75 datasets covering 32 species had been received. Data collected by the Constant Effort Sites (CES) Scheme showed that the mild winter of 1997/98 had allowed good numbers of resident birds to survive; there were statistically significant increases for both Wren and Robin. These early breeding residents also produced good numbers of young, in contrast to species that breed later in the season. The population of Blackcaps was at an all‐time high on CE sites but nine species (Sedge Warbler, Lesser Whitethroat, Whitethroat, Garden Warbler, Chaffinch, Linnet, Redpoll, Bullfinch and Reed Bunting) were at their lowest level since CES ringing began. The declines of Linnet, Redpoll, Bullfinch and Reed Bunting are of particular conservation concern. The number of birds ringed in 1998 (777,002) was three percent down on the total for 1997 and eight percent down on the five‐year average (1993–1997). The recovery total(11,628) was four percent greater than for 1997 but remains low (six percent below the five‐year average for 1993–1997). Recoveries of 174 BTO‐ringed birds and 130 birds ringed abroad are presented in the report, including a number of significant movements of an unusual nature. Particularly noteworthy were: a Blue‐winged Teal from Newfoundland, a Knot from Italy, a Short‐eared Owl in Morocco, a Swallow in Iceland, a Wren from Sweden and a Willow Warbler to, and Chiffchaff from, Rybachy in Russia.