Environmental Engineering Reference
In-Depth Information
Outbreaks of eared doves in South America have occurred where two common/anthropogenic
factors meet. Firstly, waste from mechanical harvesting provides abundant grain based food through-
out the year, and secondly, the mosaic landscape with large homogeneous patches of dense vege-
tation is highly suitable for colonial breeding. This commonly occurs close to cropped fi elds, for
example in sugarcane plantations in the southeast of Brazil (Bucher and Ranvaud 2006). In addition,
large-scale deforestation in southeast Brazil has swept away 92 to 97% of the native vegetation
(Ranvaud, Freitas, Bucher et al. 2001). Such factors can favour vast breeding colonies, some cover-
ing 40 to 1 000 hectares, and fi ve and ten million breeding birds may be located in such sugarcane
fi elds (Ranvaud and Bucher 2006).
Over the past 30 years, eared dove numbers have risen dramatically throughout such regions.
Farmers in the 1980s reported widespread damage to crops, as birds fed on emerging soybean
seedlings and enormous fl ocks landed in rice and wheat plantations (Ranvaud, Freitas, Bucher
et al. 2001). Control measures were initiated which included the intensive destruction of nests.
Eggs and chicks were collected during the day, and adults were caught at night, with the help
of torches. Chicks and eggs were buried alive and adults were collected and consumed by farm
workers. Although Brazilian wildlife protection laws do not allow hunting (Federal Law 5197 of
1967), expeditions to gather doves were organised by the Brazilian Institute of Environment and
Renewable Natural Resources (IBAMA). The IBAMA authorised the gathering and consumption
of the doves, but not the sale or direct poisoning of them (Ranvaud, Freitas, Bucher et al. 2001, and
authors' personal observation).
However, during the 1990s, many farmers did deliberately poison the eared doves, offering
them carbofuran plus Rhodamine B treated wheat grain along the soybean plantation lines. This
caused the deaths of thousands of eared doves and of many other granivorous birds (
Columbidae
,
Emberezidae
,
Icteridae
) and predators (through secondary poisoning), mainly owls (
Strigidae
and
Falconiformes
). Such intentional poisoning continued for circa ten years (personal observation).
Besides disrupting the ecological balance within affected regions, human and animal consumption
of eared doves that were deliberately poisoned or exposed to dangerous pesticides (like carbofuran
and others in agricultural fi elds) represented a real risk of intoxication via secondary poisoning for
rural workers and predatory/scavenging fauna. These practices have been undertaken for circa 20
years (until recently), yet efforts to eliminate the eared dove have proven ineffi cient. Their popula-
tion density remains high in certain regions, and they continue to seriously damage crops (Ranvaud,
Freitas, Bucher et al. 2001; Bucher and Ranvaud 2006; Ranvaud and Bucher 2006).
Evidence from other locations (Bucher and Ranvaud 2006) suggests that a lower food supply
maintains smaller populations of eared doves with no damages to the agriculture, but, for this, it is
necessary to keep the agricultural landscape under less intensive uses, with a lower proportion of
areas producing grains throughout the year.
In States such as São Paulo, Paraná, and Goiás, the conservation of biodiversity ( just like the
ecological balance in agriculture) greatly depends on the permeability of the landscape to native
species in the private properties, because areas of semi-deciduous Atlantic Forests and Cerrado (a
savannah-like biome) are now extremely diminished, fragmented and selectively harvested (Alho
and Martins 1995; Durigan, De Siqueira and Franco 2007; Diniz-Filho, Oliveira, Lobo et al. 2009;
Ribeiro, Freitas, Bucher et al. 2009). Likewise, the Federal and State protected areas are few, small,
badly-distributed, and managed with rather poor resources (Almeida and Almeida 2003; Lairana
2005; Olmos 2005; Fonseca, Lamas and Kasecker 2010; Melo, Pinto and Tabarelli 2010). Even in
some large and well-managed North American parks, species fragmentation and isolation, driven by
an increasingly anthropogenic landscape, which is scarcely permeable to wildlife, may cause local
extinction, as is the case for 14 mammal species (Newmark 1987).
Thus, in order to avoid exceeding pest outbreak thresholds (Bucher and Ranvaud 2006) and
biodiversity extinction thresholds (Andrén 1994; Fahrig 2002; Fahrig 2003; Radford, Bennett and
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