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products can then be compared and confirmed with laboratory toxicity studies
or limited, but highly focused, field investigations. Sheehan et al. (1987), for
example, used field data on the effect of carbaryl (specifically the ability of
ducklings to obtain enough invertebrate prey for adequate growth and maintenance
after an overspray of their pond habitat) to rank a number of insecticides
with regard to their hazard to young waterfowl. This required modeling
duckling growth as well as the persistence and partitioning of insecticides in
a pond environment. The toxicity of the insecticides to a few indicator species
in the laboratory was also factored into the final assessment.
In Canada, fenitrothion is used as a forestry benchmark compound against
which other cholinesterase-inhibiting insecticides are assessed (Busby et al.
1989).
Crop and use-pattern enquiries
It is not always possible to focus a wildlife investigation on a single pesticide.
In a number of cropping situations, a variety of different pesticides is used in
quick succession making the identification of compound-specific impact difficult.
This is especially true in crops where the cosmetic appearance of the
product is deemed to be important and no amount of damage is considered
permissible.
Where treatment is so complex that it is difficult to assess exposure to any one
pesticide, two approaches are possible: treated sites or landscapes can be
compared to untreated areas; and the "severity" of treatment (the a priori
expectation of toxicity) for any given site can be used as a variable against
which a number of different parameters (such as reproductive success) can be
assessed through regression analysis. Caution must be exercised in comparing
treated and untreated areas because they are likely to differ in several ways
making interpretation difficult. In Canada, these approaches have recently
been used to investigate the impact of multiple sprays on the bird fauna of
fruit orchards and to compare the number and diversity of wildlife in conventional
farms and "organic" farms (where synthetic pesticides or fertilizers are
not used).
Population enquiries and baseline wildlife surveys
Regional or national survey data of wildlife population levels are rarely
adequate to demonstrate pesticide impacts. However, in the case of some
particularly damaging compounds (e.g., DDT and dieldrin), it has been possible
to document regional and near-global population effects. Granular formulations
of carbofuran may also have the potential to affect population levels
of a number of bird species (EPA 1988).
Although systematic survey data are not usually available in the developing
world, local lore and indigenous knowledge of the local fauna should not be
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