The assessment of pesticide hazards to birds: the problem of variable effects

The hazard presented to birds by the use of a particular pesticide is dependent on many factors and may therefore vary in its severity. Even effects which occur very infrequently may sometimes be sufficiently severe to warrant regulatory action. The potential for variability is illustrated by the effects of carbophenothion on geese and of fenitrothion on forest songbirds. Potential for the movements and behaviour of birds to vary their exposure to pesticides is illustrated using data on Tree Sparrows Passer montanus and Brent Geese Branta bernicla . Methods used in the assessment of pesticide effects are reviewed, and their ability to cope with variability is discussed. Further research is required to extend understanding of the mechanisms which cause variability, and to assess the sensitivity of methods for monitoring the effects of pesticides during commercial use.