The distribution and feeding ecology of gulls on the tidal reaches of polluted rivers in North East England

Abstract

The study was concerned with investigating the manner in which six species of gulls utilized a tidal river habitat and with studying the factors that influence their distribution in this habitat. The study areas were on the tidal reaches of the Rivers Tyne, Wear and Tees. Regular censuses were taken of the numbers of gulls of each species in the study areas and their distribution was studied in relation to a number of factors which included the amount of sewage entering the section, the amount of mud exposed along the banks at low tide, the degree of urbanization along the banks of the sections, and the width of the river. The various species were found to be affected differently by the factors studied. From the census data observations were made on the seasonal variations in the number of gulls along the rivers. An investigation was made of the feeding behaviour and food preferences of the gulls frequenting the rivers. The study indicated that the species concerned had specialized in their food preferences and feeding methods so that the food sources present were used by one or more species. Detailed work was done on the effects of tide and time of day on the feeding patterns of Common and Black-headed Gulls and some detailed studies were made on the distribution of gulls feeding on the rivers in relation to sewage outfalls. Observations were also made on the preferred resting places of the gulls along the rivers. The relative importance of sewage outfalls as feeding sites gives a means of predicting the effects of proposed reduction of sewage pollution of the river. Such sections are likely to affect the Black-headed, Herring and Greater Black-backed Gulls to the greatest extent and the Kittiwake least.