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e more stringently reviewed. In Canada, the forestry insecticide fenitrothion
is currently under regulatory review. Although fenitrothion is not as acutely
toxic as a number of other anticholinesterase insecticides used in agriculture,
its impact on birds may make the product unacceptable for broad-scale forest
spraying (Busby et al. 1989). Evidence against this product is primarily in the
form of data indicating severe and widespread inhibition of brain acetylcholinesterase
in several songbird species. Similar levels of inhibition have
been associated with a number of sublethal reproductive effects as well as
some mortality. Fenitrothion is readily absorbed dermally and birds may be
at risk merely through exposure to the spray cloud (Mineau et al. 1990).
Avicides
The use of avicides in North America is limited and most bird control in
agricultural areas is nonlethal. However, one product, fenthion, is widely used
in Africa for the control of the Red-Billed Quelea (Quelea quelea). Fenthion
(queletox) is an organophosphate with exceptional dermal penetrating properties.
The common method of applying this avicide is by spraying roosts at
night using aircraft. In Canada, it is registered to control Rock Doves (Columba
livia), House Sparrows (Passer domesticus), and a variety of icterid species
(primarily Agelaius phoeniceus). However, fenthion spraying is not permitted,
and exposure must be achieved by means of a fenthion-impregnated perch.
Target birds have only to land briefly on such perches to contract a lethal dose,
but may fly for several hours before dying.
Even under these conditions, which minimize contact, raptors are extremely
vulnerable to secondary poisoning if they should prey on a contaminated bird
(Hunt et al. 1991). Furthermore, target birds that have come into contact with
treated perches are much more vulnerable to predation than unexposed
individuals, thus increasing the risk of secondary poisoning (Hunt etal. 1992).
The use of fenthion as an avicide is likely to have serious consequences on the
local raptor community as well as on any scavenger.
Rodenticides
Rodent control is a relatively minor agricultural practice in the developed
world. In developing countries, however, people are often in direct competition
with rodents for both stored and standing crops. Rodenticides are not
specific to their intended targets and can have a significant impact on nontarget
species. Only detailed knowledge of the habits of the target species and
use of specific baiting locations or specialized bait holders can reduce the
taking of "innocent" species.
More problematic is secondary poisoning. The newer, more efficacious anticoagulants
present an even greater hazard to predators than the older products
(Wenz 1984; Hegdal and Colvin 1988). Compounds such as difenacoum,
brodifacoum, flocoumafen, and similar "super" coumarin-type products
should not be used in situations where the target species is likely to be preyed
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