Impact of - IDL-BNC @ IDRC - International Development Research ...

upon or scavenged. Generally, the use of these products should be restricted
to human dwellings and grain-storage areas. Other strategies should be
employed for field-control of rodent pests.
The use of endrin to control rodents in orchards in North America has severe
consequences for raptors (Blus et al. 1983) and is clearly unacceptable. The use
of DDT to control bats is also ill-advised and resulted from the mistaken notion
that bats were more sensitive to DDT than other mammals. This is true only
when bats are awakened from their hibernacula and have low levels of body
fat. Moreover, DDT does not always provide lethal control and can actually
increase the risk that humans will be bitten by debilitated bats.
Some products that potentially give rise to secondary poisoning can be used
safely under conditions that restrict the availability of the affected target to
predators or where the predator, through its normal feeding practice, discards
the dangerous body part(s). Strychnine, for example, is likely to be dangerous
only when the predator consumes the gastrointestinal tract of the affected
target. This characteristic limits exposure of some raptor species even though
they may consume large numbers of contaminated prey.
To limit secondary poisoning, zinc phosphide is probably the best product
available. Its use should be encouraged where it is of sufficient efficacy. Again,
on ecological grounds, care should be taken to preserve the raptor population
of any given area because they are an integral part of a long-term rodentcontrol
strategy.
Studying and monitoring the impact of
pesticides on wildlife in the field
Compound-specific enquiries
Because of the requirements for registration, compound-specific enquiries are
the most common type of wildlife investigation used to demonstrate the safety
of a particular pesticide. However, no single strategy is adequate for all
situations. It is often best to start with testable hypotheses, then devise ways
to prove or disprove these hypotheses.
In probabilistic terms, type I errors (i.e., concluding that there has been an
effect from a pesticide when there have been no effects) are uncommon. For
example, when wildlife mortality is encountered in a treated field, the probability
that this mortality resulted from reasons unrelated to the application are
small for the simple reason that it is uncommon to witness random wildlife
mortality under normal circumstances.
On the other hand, the probability of type H errors (i.e., failure to detect an
occurring problem) is much higher. Often the implicit assumption is that all
effects are observable. In practice, however, this belief is not always tenable.
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