Environmental Engineering Reference
In-Depth Information
Field personnel conducted three pre-treatment and three post-treatment surveys on three centrally
located plots of 300 by 600 metres. The personnel also tried to fi nd nests and collected some birds
(by shooting) for cholinesterase measurement.
Two of 11 common breeding species showed a signifi cant decline in the post-spray period rela-
tive to the pre-spray period. Although declines in those species were also seen in the control plot,
they were not signifi cant. Nest success rate was 46% (17/37) for treatment nests versus 83% (10/12)
for the controls. This difference is statistically signifi cant (X
2
5.12, P
0.024). The researchers
believed that most of the nest losses were due to predation. However, nest losses did not seem to
peak on days one to three post-spray, when, based on the characteristics of carbofuran, one would
expect to observe a toxic effect on the adults or young.
As one can best determine from the data provided, the researchers collected seven songbirds
by shooting on the day of spraying (four horned larks, two red-winged blackbirds (
Agelaieus
phoeniceus
), and one brown-headed cowbird (
Molothrus ater
)). Because spraying occurred over an
extended period, it is impossible to determine whether the researchers collected all birds from areas
already sprayed. Four of the seven exhibited a reduction in brain cholinesterase of more than 20%
(three of the four horned larks and one red-winged blackbird). Maximum cholinesterase depres-
sion was 61% in the larks, and the blackbird showed a 52% reduction in activity relative to control.
None of the three birds sampled one day post-spray (one red-winged blackbird, one vesper sparrow
(
Pooecetes gramineus
), and one eastern kingbird (
Tyrannus tyrannus
)) exhibited brain cholinesterase
depression greater than 20% (refer back to the discussion in Chapter 2).
The researchers established and ran a live-trap grid for ten nights pre-spray and seven nights post-
spray and placed snap traps away from the grids to collect individual mammals. Irvine (1987) stated
that there did not appear to be any day-to-day shift in the relative ratios of new to recaptured animals
during the post-spray period. However, the data presentation does not allow one to look specifi cally
at the survival of animals marked before the spray in the post-spray period. Also, inconsistencies
between the tabular data and a fi gure preclude meaningful interpretation. The populations studied
appear to show a very high rate of turnover in both the pre-spray and post-spray periods. Despite ten
consecutive nights of trapping, recapture numbers remained consistently below the number of new
captures for most of the pre-spray period.
The researchers snap-trapped only one deer mouse (
Peromyscus maniculatus
) on the night after
the spray, and it had a brain cholinesterase inhibition level of about 45% relative to control. The
researchers sampled three more small mammals about one week post-spray. One sagebrush vole
(
Lagurus curtatus
) exhibited a low cholinesterase level, but not to the extent of being diagnostic.
8.4.2.3 Fox et al. 1989
At the time of this study, burrowing owls were offi cially listed as 'threatened in Canada'; their
status has now been upgraded to 'endangered'. In 1986 and 1987, the Canadian Wildlife Service
commissioned fi eldwork to investigate the impacts of operational grasshopper spraying on the
species. The following summary is from the fi nal report by Fox, Mineau, Collins et al. (1989) that
outlined the research and resulting analyses in great detail.
The data of Fox and colleagues showed conclusively that, in 1986, carbofuran applied at
132 g ai/ha had a signifi cant impact on the survival and reproductive success of burrowing owls.
There were signifi cant declines in nesting success (P
0.002) and brood size (P
0.006) with
increasing proximity of carbofuran spraying to the nest burrow. In this case, Fox, Mineau, Collins
et al. (1989) defi ned nest success as the proportion of burrows that fl edged at least one young. No
trend of lowered reproductive indices with increasing proximity of spray was observed either for the
insecticide carbaryl or for all insecticides other than carbofuran pooled together. Overspraying of
the burrows with carbofuran caused an 83% reduction in brood size and an 82% reduction in nesting
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