The feeding ecology of young Mallard (Anas platyrhynchos) and Tufted Duck (Aythya fuligula) in wet gravel quarries.

Abstract

The drainage of natural wetlands for agricultural and other purposes continues to reduce the breeding habitat available for wildfowl in Great Britain. Flooded gravel quarries provide the largest single factor acting to reverse this trend. There is great public pressure for recreational facilities on these new inland waters and wildfowl breeding sanctuaries must be integrated into multi-purpose schemes. A detailed investigation of the factors causing juvenile mortality in this specialized environment is therefore essential. The invertebrate faunas of flooded gravel quarries are usually restricted in both numbers of species and numbers of individuals when compared with similar natural waters. The food eaten by and available to young mallard and tufted duck is discussed with specific reference to the diverse environments which can be provided by the gravel industry. The gut contents of individual ducklings were examined and related to the potential food organisms found to be present in the environment. Fauna sampling was by means of timed pond-net sweeps and quantitative grab samples of the bottom deposits. Very young mallard ducklings fed mainly on insect imagines while older ducklings adopted a largely vegetarian diet which reflected the composition of the local flora. The food of very young tufted ducklings consisted mainly of molluscs and planktonic crustacea. The Gastropod mollusc Potamopyrgus jenkinsi is an important food item throughout the life span of the tufted duck in this environment. Wet gravel pits form a more favourable environment for breeding tufted duck than for mallard though the deliberate creation of wildfowl areas during extraction and subsequent restoration can supply the needs of a diverse wildfowl fauna