Impacts of carbofuran on birds in Canada and the United State - Carbofuran and Wildlife Poisoning: Global Perspectives and Forensic Approaches - page 238

were in poor body condition and had probably just returned from migration. They may also have
been feeding on food contaminated by the insecticide. However, nearby cornfi elds were treated with
granular carbofuran, which was another potential source of the insecticide (Roth 1986).
8.4.4.2.2 June 1986, grasshopper control, Moose Jaw, Saskatchewan
Field personnel found an estimated 45 gulls convulsing after feeding on grasshoppers in a fi eld that
had been treated with carbofuran a few hours earlier. Carbofuran residue levels in grasshoppers
retrieved from the oesophagi of the birds ranged from 4.2 to 7.2 ppm (Leighton and Wobeser 1987;
Leighton 1988).
Residue levels measured in the dead gulls in this incident were on the high end of the range
of levels expected from a normal application to control grasshoppers. Irvine and colleagues (refer
to Section 8.4.2.2) reported peak grasshopper levels ranging from 0.45 to 6.6 ppm after an aer-
ial application with 132 g ai/ha. Two samples of grasshoppers collected after an experimental
ground application contained a mean of 2.5 ppm, but a gullet (i.e., oesophageal) sample from a gull
shot and collected from the plot contained 5.7 ppm carbofuran.
8.4.4.2.3 August to September 1985, Alberta
Two other incidents involving gulls and possibly linked to carbofuran use in Alberta are not very
well documented. About 70 ring-billed gulls (Larus delawarensis) died in August 1985 after eat-
ing grasshoppers. Carbofuran was suspected because of its popularity for grasshopper control but
investigators did not analyse the samples for residues. Another 11 ring-billed gulls died at a different
Alberta location in September, and their gut contents contained 2.7 ppm carbofuran. September is
unusually late for grasshopper spraying, and the circumstances surrounding the kill remain unclear
(Somers, Khan and Hawley 1988). During 1985, there was extensive spraying for grasshoppers in
the Canadian prairies.
8.4.4.2.4 May 1988, corn, Le Bayou Noir, Louisiana
A biologist from the Louisiana Department of Fisheries and Wildlife reported that approximately
(the birds were badly scavenged making an exact count diffi cult) 200 cattle egrets ( Bubulcus ibis )
died in a fi eld seeded three weeks previously (Mullins 1988). The farmer, when questioned, related
that he had sprayed liquid carbofuran directly into the seed furrows. However, the Commissioner
of Agriculture for Louisiana (Odom 1988) contested this version of the facts and suggested that
the farmer had instead treated his corn seed directly with the insecticide. He surmised that the
egrets had actually fed directly on badly incorporated seed. The record does not indicate who was
proven right. Problems resulting from the use of carbofuran as a seed treatment were outlined in
Chapter 7.
8.4.4.2.5 April 1991, corn, King George and Isle of Wight Counties, Virginia
Fite, Randall, Young et al. (2006) reported that observers collected 51 carcasses from 22 different
species near a corn fi eld sprayed with carbofuran. This incident stands out for the sheer diversity of
species killed by the pesticide. Given the timing and prevailing use pattern, this would have been a
soil application, probably associated with seeding. Fite and colleagues report that brain cholineste-
rase levels and residues in the gastrointestinal tracts confi rmed the diagnosis.
In a similar incident, also confi rmed by residue identifi cation and cholinesterase assays, observers
reported another 51 birds and one small mammal carcass from more than seven different species.
8.4.4.2.6 April 1992, alfalfa, Caroline County, Virginia
Observers found two common grackles and four mourning doves by a watering hole in proximity
to a treated fi eld (Fite, Randall, Young et al. 2006). A combined sample of the grackle's gizzards
contained 15 ppm carbofuran but no residues were detected in the only two doves tested. A water