Environmental Engineering Reference
In-Depth Information
completely covered with soil during mechanical seeding, are eaten by granivorous birds foraging for
food. This can then lead to direct mortality by deliberate ingestion or secondary poisoning, if preda-
tors ingest these poisoned birds. This problem is not confi ned to Brazil, but is also an issue in many
countries where agrotoxin-laden seeds are used.
The majority of alternative methods used to mitigate bird mortality, due to poisoning from car-
bofuran and other pesticides and/or to avoid damages in several types of plantations, have involved
scaring birds away from the area and preventing them from ingesting seeds with the use of acoustic,
tactile, visual and/or gustative repellents. However, these measures, which add to the operational
and fi nancial burden of the agricultural operations, are not entirely satisfactory, and can themselves
cause serious suffering to wild birds (Dolbeer, Ingram, Seubert et al. 1976; Avery, Humphrey, Primus
et al. 1998).
Notwithstanding these fi ndings and critical public opinion, studies have been developed
to identify suitable chemical repellents and/or repelling colours (Tobin 2002; Hartley, Waas,
O'Connor et al. 1999; Hartley, O'Connor, Waas et al. 2000) in an attempt to minimise the risk
of poisoning wildlife with pesticides (Avery 2002). Preferences and aversions of animals for
food are often related to the taste or appearance of the possible alimentary item (Zuberbuehler,
Messikommer and Wenk 2002). Nevertheless, the fact that birds have a poorly-developed gus-
tatory sense is a plausible reason for the limited results obtained by Avery, Humphrey, Primus
et al. (1998) and Moran (2001), both of whom used chemical repellents in the absence of alterna-
tive food sources.
Birds tend to avoid primary repellents because they irritate their peripheral senses (i.e., taste,
touch, smell, and hearing). Repellents that cause gastrointestinal injury are deemed secondary
repellents. In this case, animals potentially learn to avoid such substances after an initial ingestion/
exposure period. Secondary repellents are generally derived from agricultural pesticides, and are
more effective. Primary repellents are commonly derived from natural products, and are pro-
moted as causing less environmental impact, although they may also be less effective (Sayre and
Clarck 2001).
Birds often use agricultural areas to feed on the abundant and accessible food resources available.
If food is diffi cult to fi nd, chew or digest, birds will spend more time and energy foraging. If birds
are fi nding it diffi cult to maintain a positively-balanced ratio between energy spent over food gained
(the theory of optimum foraging), they will search for new areas where food sources are more readily
available (Avery 2002; Begon, Townsend and Harper 2006).
Camoufl age is an evolutionary adaptation that can decrease an individual's chance of being
detected within its environment (Zug, Vitt and Caldwell 2001; Frankel, Sousa, Cowan et al. 2004;
Merilaita 2003). By using this principle a seed of wheat, corn or rice could fi rst be treated with a
systemic defence (e.g., a pesticide), then be treated with a dye to make it similar in colour and texture
to the soil. This measure may ensure that any seed not fully buried by mechanical sowing, though
technically exposed to a bird, is effectively camoufl aged against the soil backdrop by other organic
matter and surface irregularities. Thus, if effective, camoufl aging could prevent the identifi cation/
detection of toxic seeds by birds in that area actively searching for them on the ground.
The camoufl aged coated seed that we used in previous work had a surface that was dark brown,
rugged and opaque. The use of this seed resulted in reduced consumption, and, consequently, reduced
mortality of birds when compared with wheat and rice seed dyed with Rhodamine B (Almeida,
Couto and Almeida 2010a). In addition, the camoufl aged corn seeds were removed less frequently
from the agricultural fi elds, in turn benefi ting the farmer (Almeida, Couto and Almeida 2010b).
These fi ndings can be explained because the brown seeds were probably absent or less obvious
in the avian search image (Begon, Townsend and Harper 2006). Also, the seeds contrasted less
against the soil background, hence their contours were less visually evident. The brown colour and
the powder dye used, which is rich in iron oxide, decreases the spectral refl ectance of the seed
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