Environmental Engineering Reference
In-Depth Information
iv) falling of seeds on compacted ground or on surfaces with no organic matter
v) large concentrations of birds in the immediate area
For example, during experiment 6, birds often concentrated within the treatment plot in areas
some distance from where tractors were actually operating. It is important that, while there is sown
seed on the soil surface, farm machinery must be used in a way that does not scatter (or scare) birds
into areas where carbofuran treated seed is exposed and readily available.
In addition, in areas of forest that have recently been cleared (as was the case in experiment 3),
or, when no tillage is used, waste vegetation, roots, thickets, branches and logs may all hinder seed
burial, again increasing the risk that birds will be exposed. Zero tillage has been used widely in
Brazil, where seed is sown onto un-ploughed land (which maintains remnants of the previous crop).
Also, in order to attain better germination, farmers may adjust their sowing machines so that seeds
are buried only a few centimetres (~5 cm) below the surface.
Sowing machine operators will also often manoeuvre machines whilst still spreading seed. This
means that seed volume per unit area can be excessive, or seeds are spread outside the planting area,
i.e., onto compacted dirt roads lacking organic matter. Seeds are then far more visible to birds, and
stand out. This increased conspicuousness results in high mortality, which is often recorded near the
roadside.
In experiment 2, adjacent to the experimental plot, was a recently harvested rice crop. This
area offered abundant food, attracted a large number of birds, and hence mortality in our experi-
mental plot was not mitigated (to an acceptable level) by camoufl aging the seeds (Almeida 2006).
Depending on the site and time of year, very high numbers of birds can be attracted to rice, wheat
and sugarcane plantations. The latter can be especially attractive to eared doves which fl ock there
in search of overnight refuge, and a place to nest. Thus, when there are known to be high numbers
of birds in an area immediately surrounding a proposed planting site, farmers should ideally delay
seeding, or harvest the crop which is attracting the birds (Hawthorne 1987).
Where eared dove fl ocks were present, the minimum number of birds poisoned was between
25 and 183 (excluding experiment 3, where no dead birds were found, which we view as atypical;
see Table 7.3). Thus, in plots where there was mortality, the average plot size was 8.54 hectares (n
6; standard deviation 7.8). The estimated number of birds expected to be poisoned was therefore
77.5 ± 55.7 (n 6; standard deviation 69.6, 0.05). Therefore, we would expect an average of
approximately nine deaths per hectare, at a minimum rate of 2.5, and a maximum rate of 15.6 birds
per hectare.
Such estimates need to consider that the mortality caused by carbosulfan was probably not accu-
rate because birds escaped into the surrounding habitat before dying. Moreover, counts did not
provide a full tally of secondary poisoning mortality rates of predators who left the area or those
carcasses removed by scavengers before being counted (as described by Mineau 2005). The above
estimates are therefore conservative. They are, however, similar to those made for North America in
corn crops, where carbofuran was used in granular form. Here, in Iowa and Illinois, between three
and 16 dead birds were estimated to die per hectare (Mineau 2005). Such a comparison is valid, since
similar methods were used when searching for dead birds. Also, consumption rates for rice, wheat
and corn seed by birds on such farms is often similar (Almeida, Couto and Almeida 2010b).
These estimates regarding the number of birds potentially poisoned on Brazilian farms are very
worrying. Agrotoxins like carbofuran are used on a very large scale in Brazil, and improper use
occurs throughout the agricultural landscape. Governmental control is severely lacking and mil-
lions of hectares are devoted to rice, wheat, and corn production. Species such as the eared dove
are abundant in some regions, and they may be both victims and vectors, effectively passing
the agrotoxin legacy up the food chain to predators (some of whom may be rare) as the poisoned
doves are predated or scavenged.
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