Nationally important wintering populations of up to 2700 Pochard Aythya ferina and 2000 Tufted Duck A. fuligula feed around Salford Docks in the upper reaches of the Manchester Ship Canal. The system is grossly organically polluted and devoid of aquatic macrophytes, but holds high densities of oligochaetes and other pollution-tolerant invertebrates. The species fed together and differences in feeding distributions were more apparent between day and night than they were between species or winter period. We related the spatial patterns of feeding by ducks to water depth, channel width, total organic benthic carbon levels, and invertebrate densities. Separate analyses were performed for each species, during nighttime and daytime, and for different periods of the winter. In only half these analyses could feeding patterns be explained by differences in the microhabitat variables. However, feeding by both species was concentrated in the wider portions of the docks, in areas with high densities of oligochaetes, but particularly in areas of high total benthic organic carbon. These were areas where large amounts of sewage matter are deposited in the benthos. There are plans to improve water quality in the docks by modernizing sewage treatment systems upstream and by oxygenating the water within the docks. These may generally improve the biology of the system , but they may have a serious impact on the numbers of diving ducks by reducing the densities of their invertebrate prey.

A variety of organic contaminants can potentially have impact on aquatic birds by their affecting surface tension. Avian plumage constitutes a porous barrier to water and the air trapped between the feathers serves as thermal insulation. When the air is displaced, the birds expend extra energy to maintain a normal body temperature, but this response cannot be sustained for long, especially at low environmental temperatures. When energy stores are depleted, hypothermia and death ensue. Surface tension is the force that resists infiltration of water into the plumage. The critical surface tension for feather wetting is conservatively estimated to be in the range 38–50 mN m-1. The hypothesis that surface-active organic contaminants can have significant detrimental effects on aquatic birds was evaluated. New data obtained in a study of water penetration pressures in Lesser Scaup contour feathers show that the 'wettability safety factor' is reduced by about half during moult. That is, the critical surface tension was raised to approximately 49–58 mN m-1 in moulting Lesser Scaup. The energetic and behavioural effects of oil contamination are reviewed, and it is concluded that even small quantities of organic material may confer significant physiological cost. The available data generally support the hypothesis that waterfowl face a potential risk associated with chronic or periodic mild depression of water surface tension due to organic pollutants, including oils and detergents. However, much of the evidence is indirect and further research, especially long-term assessment of surface tension in marine, estuarine and freshwater habitats, is needed to determine whether a real environmental problem exists.

The purpose of this study was to adapt the ethoxyresorufin O-deethylase (EROD) assay to the microplate technique. In addition to showing the practical advantages related to the intrinsic properties of such systems, we wished to demonstrate their potential value for biological monitoring of contamination in natural environments. A simpliffed procedure was developed for the preparation and fluorimetric assay of EROD activity using only basic laboratory equipment. The use of plate readers allows measurements to be done rapidly and provides numerous advantages in comparison with traditional methods. Within the context of our study; this test could be substituted to advantage for the enzymelinked immunosorbent assay (ELISA).