Environmental Engineering Reference
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that egg survival and hatching rates did not differ between control and treated nests. Nestling
mortality was signifi cantly higher in treated nests than in control nests in one of the two site pairs
only, but no dead nestlings were found. Predation was higher in treated sites, but abandonment was
higher in control sites. Several nestlings sacrifi ced for analysis contained residues of carbofuran.
Taken together, these studies did not demonstrate any convincing effect of carbofuran at
132 g ai/ha on nesting Brewer's blackbirds. There were too few data on the other species in Horstman
(1985) to reach any conclusions. The following factors limited the usefulness of these studies:
1. No grasshopper outbreak occurred during the 1987 study, and birds may therefore not have
been exposed to large numbers of contaminated prey. Although the birds principally foraged
in the ditches in the 1985 outbreak year, in 1987 they mainly foraged in adjoining fi elds.
2. During the 1987 study, it rained soon after spraying. This affected both nests in the egg stage
(1.5 to 5 hours between spray and rain) and those in the nestling stage (12 to 16 hours between
spray and rain). In the fi rst case in particular, the incorporation of the insecticide into the local
insect biomass may have been reduced.
3. Due to unforeseen delays, in 1987 the spray truck was fi lled the day before spraying. Although
the water used in the truck likely was not alkaline enough to cause signifi cant degradation
of the carbofuran, it is likely that insuffi cient agitation caused uneven application of the insec-
ticide (L. Horstman, personal communication). The investigators did not take samples to
confi rm the uniformity of the concentration of carbofuran in the spray solution.
8.4.2.2 Irvine 1987, 1990, Forsyth et al. 1989, Forsyth and Wescott 1994
These three reports and this publication summarise the available data on a large-scale experimen-
tal carbofuran spray, carried out in 1987, and a smaller application, made in 1988. Field personnel
sprayed a large grazed pasture with native grasses (259 hectares) with fl owable carbofuran at a low rate
(140 g ai/ha). Forsyth, Jackson, Westcott et al. (1989) also established a control site for comparison. The
impact work consisted of looking at small mammals and birds from the central cores of the two blocks.
Field personnel used a series of 24 randomly positioned transects monitored with spray deposi-
tion cards. Average droplet numbers ranged from one to 24 per square centimetre.
Pooled samples of dead grasshoppers collected with forceps from the same area contained
average carbofuran residues of 2.1 ppm one to three hours post-spray and 2.5 ppm six to nine hours
post-spray (Forsyth and Westcott 1994). Grasshoppers collected in sweep net samples (which
included both living and dead grasshoppers) contained residues ranging from 0.45 to 6.6 ppm carbo-
furan on the day of spraying, which declined rapidly on successive days.
Residues on vegetation samples taken from 0.25 square metre quadrats averaged 13.3 ppm one to
three hours post-spray and 5.9 ppm ten to 11 hours post-spray. Overall, on the spray day (18 June),
vegetation samples had residues ranging from 1.1 to 21.8 ppm. On 19 June, the residues ranged from
1.2 to 21.7 ppm. A light rain (3 millimetres) fell on 19 and 20 June, likely reducing the pesticide
residues on the vegetation. Samples taken on 20 June ranged from 0.1 to 1.1 ppm.
Field personnel fi rst searched the area between eight and nine hours post-spray. They searched
less than 1% (about 0.7% or 1.9 hectares) of the total spray area, over a three hour period
and repeated the search 32 and approximately 150 hours post-spray. The searchers did not fi nd any
dead or moribund birds. However, the small area searched, the minimal amount of time devoted
to this activity, and the breeding density (approximately four breeding pairs per hectare for all the
regular bird species combined) would have made it diffi cult to fi nd carcasses even if there had been
mortality. Furthermore, it does not appear as if the investigators determined search effi ciency or
carcass disappearance rates.
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