Duckling mortality in the Shelduck, in relation to density, aggressive interaction and weather

Abstract

The daily mortality rate of ducklings of the Shelduck Tadorna tadorna increased significantly with density of broods on the Ythan estuary, Aberdeenshire, in two of four years (1975-1978). Aggressive interaction between broods increased significantly with brood density in both of two years and this was confirmed by crowding experiments. The daily mortality rate of ducklings also tended to increase with increasing frequency of aggressive interaction between broods. The overall survival of ducklings in any year increased significantly with increasing number of warm days in the season and decreased significantly with more windy days. There was no correlation between survival and either the number of rainy days or the number of ducklings hatched. The daily mortality rate of ducklings increased significantly with adverse weather in all four seasons. Although different weather variables were involved in different years, duckling mortality increased significantly with low temperature in all four years, with high wind speed in three, but with rainfall in only one year. Duckling mortality tended to increase with worsening weather only in years when that weather factor was more severe than average and the mortality tended to follow one day after a worsening of the weather, rather than occurring immediately.