Methods for estimating the proportions of icelandic and british redshanks tringa totanus in mixed populations wintering on british coasts

Abstract

Both British and Icelandic Redshanks may be found in Britain in the non-breeding season. They are indistinguishable, though their average measurements differ. Samples of breeding Redshanks were caught in Iceland and Britain to collect biometric information to he used to estimate the proportions of Icelandic and British Redshanks in mixed winter populations. Wing, bill and foot were the only structures whose lengths were significantly different between the 2 populations and which could be measured with reasonable precision. Two methods were used to estimate the proportions in mixed samples: Discriminant analysis and a maximum likelihood analysis of Mixtures of Normal distributions. A simple graphical method based on the discriminant analysis was devised. The methods resulted in similar estimates of the proportions of Icelandic Redshanks when used on mixed samples. Estimates from captured samples in eastern Scotland indicated that there is an equal mix of Icelandic and British Redshanks in autumn, but that almost the entire winter population is Icelandic. Variability in measurements between and within observers was quantified and is discussed in relation to future work. © 1988 Taylor & Francis Group, LLC.