EFFECTS OF OIL AND OTHER SURFACE-ACTIVE ORGANIC POLLUTANTS ON AQUATICBIRDS

A variety of organic contaminants can potentially have impact on aquat ic birds by their affecting surface tension. Avian plumage constitutes a porous barrier to water and the air trapped between the feathers se rves as thermal insulation. When the air is displaced, the birds expen d extra energy to maintain a normal body temperature, but this respons e cannot be sustained for long, especially at low environmental temper atures. When energy stores are depleted, hypothermia and death ensue. Surface tension is the force that resists infiltration of water into t he plumage. The critical surface tension for feather wetting is conser vatively estimated to be in the range 38-50 mN m(-1). The hypothesis t hat surface-active organic contaminants can have significant detriment al effects on aquatic birds was evaluated. New data obtained in a stud y 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 approximate ly 49-58 mN m(-1) in moulting Lesser Scaup. The energetic and behaviou ral effects of oil contamination are reviewed, and it is concluded tha t even small quantities of organic material may confer significant phy siological cost. The available data generally support the hypothesis t hat waterfowl face a potential risk associated with chronic or periodi c mild depression of water surface tension due to organic pollutants, including oils and detergents. However, much of the evidence is indire ct and further research, especially long-term assessment of surface te nsion in marine, estuarine and freshwater habitats, is needed to deter mine whether a real environmental problem exists.