The breeding biology and population history of the DipperCinclus cincluson a Scottish river system

Abstract

The Dipper population of the Esk river system, Lothian, Scotland, has been surveyed at intervals over a period of 60 years up to the present day, with detailed population surveys and studies of breeding biology taking place between 1979 and 1991. Although the population has fluctuated up to 6-fold, there is no evidence of any consistent trend in population size. Currently, maximum breeding densities are higher than in most other studied Dipper populations. The breeding season begins significantly later than in populations further south and west in the British Isles, but clutch and brood sizes and the incidence of second broods are all typical of other British and European populations. Unusually in comparison with other studies in Britain and Ireland, there is no evidence of any significant decline in clutch and brood sizes towards the end of the breeding season. Although clutch size did not differ with the age of parents, breeding success of adult pairs was higher than that of pairs with at least 1 first-...