Impacts of carbofuran on birds in Canada and the United State - Carbofuran and Wildlife Poisoning: Global Perspectives and Forensic Approaches - page 242

The arrival of dead or moribund birds appeared to follow periods of rain, conditions documented
as being conducive to waterfowl mortality in fi elds treated with granular carbofuran. Laboratory
personnel either forcibly removed crop contents by hand or surgically emptied the crop in most of
the birds, who recovered very rapidly after this procedure. Again, this is consistent with poisoning
with a carbamate insecticide. In all cases, hawk and eagle crops contained duck or gull body parts.
Only nine birds were available for a proper postmortem and, for logistical reasons, it was only
possible to chemically analyse crop contents of two bald eagles and two red-tailed hawks (Elliott,
Langelier, Mineau et al. 1996). One bird contained no detectable residues, one bird had residues of
fensulfothion, and two had carbofuran. One bald eagle had levels of 200 ppm; a red-tailed hawk had
2 ppm. Ironically, the hawk with 2 ppm had signifi cantly depressed brain cholinesterase; the eagle
with 200 ppm did not. In a well-documented bald eagle kill related to the use of granular carbo-
furan in maize, one bird with a 58.6% inhibition of brain cholinesterase (diagnostic of ingesting a
potentially lethal dose) had crop content residues of 0.64 ppm carbofuran. This bird had scavenged
remains of rock doves ( Columba livia ) and blackbirds (Hill and Swineford 1985; Thomas 1985;
Patterson 1986). Chapter 2 provides a discussion of the frequent lack of correspondence between
cholinesterase levels and carbofuran exposure.
Finally, the presence of duck and gull feathers in all the birds and the apparent association of the
kills with periods of rain suggest that the birds were able to locate kills of waterfowl resulting from
insecticide use including carbofuran.
Furadan is one of the few modern pesticides toxic enough to cause secondary toxicity in birds
that scavenge primary casualties, killed from the use of the liquid formulation. In one of their own
studies, the manufacturer (FMC 1989a) reported affected (paralysed) northern harriers both in their
Texas/New Mexico study in maize and in the alfalfa study in Kansas. In the latter case, the bird was
still clutching its prey, an eastern cottontail found to contain 0.1 ppm carbofuran residues. In a 1995
incident (see 8.4.4.2.9 above) use of the liquid formulation in-furrow at seeding resulted in kills of
waterfowl, songbirds and of bald eagles that scavenged the songbird carcasses. In a 2006 incident
documented previously in Section 8.4.4.2.11, FMC personnel reported two red-tailed hawks that
died along with 100 blackbirds in an alfalfa fi eld.
8.6 Impacts resulting from abuse cases regardless of formulation
Over the years, those individuals intent on poisoning unwanted wildlife have recognised carbofuran
as an ideal toxicant. Its extreme toxicity to both birds and mammals and variation in formulation
type makes it a popular product for illegal usage. The variety of cases in terms of the bait type and
method of presentation to the target wildlife is only limited by the imagination of the perpetrator.
The subject of carbofuran abuse/misuse is dealt with extensively throughout the rest of this topic and
only major trends and tendencies will be reviewed here.
Cases of pesticide abuse are more likely to be reported than cases resulting from the legal regu-
lated use of pesticides. Perpetrators of abusive poisoning often use highly concentrated baits which
render the victims unable to venture far from the site of poisoning (the so-called 'circle of poison'
with the bait at the centre). Birds able to fl y away from a site of exposure are less likely to be
recovered and analysed for residues; authorities typically investigate cases of abuse more vigor-
ously, given the legal requirements and statutes in North America. Abuse cases are considered less
'sensitive' in that they do not refl ect on that jurisdiction's agricultural operations and they are more
likely to be publicised. The local citizenry may be reluctant to report problems stemming from
normal labelled use of pesticides if they believe the pesticide implicated to be essential to their liveli-
hood or that of someone in their community.
In a review of pesticide poisoning of birds of prey between 1985 and 1995, Mineau and col-
leagues (1999) estimated that, where this could be determined, 69 and 67% of the carbofuran incidents