Whitethroat Sylvia communis population studies during 1981–91 at a breeding site on the Lincolnshire coast

More than 3000 Whitethroats, including almost 500 adults, were ringed during 1981–91 at Crook Bank, on the Saltfleetby‐Theddlethorpe Dunes N.N.R. Adult captures peaked in 1982 and 1987–89, with a population ‘crash’ in 1984. Annual adult survival rates, estimated from between‐year recaptures, varied from 10.8% in 1983–84 to 67.7% in 1988–89, with a mean of 55.1% during 1984–85 to 1988–89, when the population was increasing. The annual ratios of juveniles:adults captured were positively correlated with April‐August rainfall. Juvenile return rates varied from 2.0% in 1991 to 10.3% in 1987, with an overall mean of 5.7%. Differences were found in return rates in the year after ringing for birds ringed either as juveniles or as adults, with significantly more males than females returning. However, there were no differences for Whitethroats returning for their second or later breeding season at Crook Bank. Estimates from ringing data suggested that there were 23–27 pairs breeding on the 8.5 ha study area infive of the years, dropping to 11 pairs in 1984–85, but peaking at 46 pairs in 1989. A mapping survey in 1987–91 recorded densities of 27–34 territories/10 ha in three years, also with a peak in 1989 (of 45 territories/10 ha). Whitethroat breeding density at Crook Bank thus appears to have been higher than recorded elsewhere in Britain, even prior to the 1968–69 ‘crash’.