The temperate Grasslands of South
America are home to a unique assemblage of Bird species, which are increasingly
being affected by habitat modification as wild Grasslands are converted to
agricultural usage. As a consequence many South American Grassland Bird species
are now at risk, with 50 species considered to be threatened in Brazil and 24
in Uruguay. While conservation in South American tropical forests has become a
matter of international interest in recent years, very little attention has
been paid to the fate of South American grasslands, with a consequence that
they have received relatively little protection; only 2.2% of all protected
areas in Brazil cover temperate Grasslands and only 1.7% in Uruguay.
Wild Grasslands are being
converted to a variety of usages in South America, including arable
monoculture, particularly Soy (Glycine
max), but also corn (Zea mays),
Oats (Avena sativa), Ryegrass (Lolium multiflorum), Wheat (Triticum vulgare), Barley (Hordeum vulgare), Sunflower (Helianthus annuus) and Rice (Oryza spp.). Many
areas have also been converted to Cattle pasture; these areas are considered to
be more natural and likely to provide a better environment for Grassland Bird
species, but are also seeded with introduced Grass species to improve the
pasture, particularly Ryegrass (Lolium
multiflorum) and Lovegrass (Eragrostis
plana). Significant areas of Grasslands have also been converted to
forestry, particularly of Eucalyptus
and Pine (Pinus spp.).
Previous studies of these
environments have suggested that natural grasslands are better environments for
native Birds than Barley or Sunflower fields or Cattle pasture in Uruguay and
that Cattle ranches were better habitats for Birds than croplands in Argentina.
In a paper published in The Condor on 14 January 2015, Thaiane Weinert da Silva of the Laboratório de Ornitologia at the Museu de Ciências e Tecnologia and Programa de Pós-Graduação em Zoologia at the Pontifícia Universidade Católica do Rio Grande do Sul, Graziela
Dotta of the Laboratório de Ornitologia at the Museu de Ciências e Tecnologia
and Programa de Pós-Graduação em Zoologia at the Pontifícia Universidade
Católica do Rio Grande do Sul and of the Conservation Science Group at the
Department of Zoology at the University of Cambridge, and Carla Suertegaray
Fontana, also of the Laboratório de Ornitologia at the Museu de Ciências e
Tecnologia and Programa de Pós-Graduação em Zoologia at the Pontifícia
Universidade Católica do Rio Grande do Sul describe the result of a study of
Bird abundances and species diversity on Cattle ranchlands and Soybean farms in
Uruguay and Brazil.
All of the sites chosen were
areas with deep soil layers with essentially flat topographies and occasional
undulating hills (coxilhas). These sites were chosen for their similarity, in
order to exclude variations in Bird populations caused by topography rather
than land-use. The Cattle ranchlands were considered to be semi-natural, with a
range of native Grasses. The Soybean sites were all former Cattle ranchlands in
their second and third years of arable cultivation. At these sites genetically
modified Soybeans were grown as a monoculture with treatment with glyphosate
(N-(phosphonomethyl)glycine); a systemic herbicide which kills non-immune plants by inhibiting amino acid synthesis, and which is widely criticized by environmentalists for its environmental persistence and ability to enter water systems, particularly since the advent of resistant crops which can encourage heavy use.
Soybeans were grown in the spring and summer at these sites, with
Wheat being grown at the two Uruguayan sites during the autumn and winter,
while Ryegrass was grown out of season at the Brazilian sites. None of these
sites was ploughed, and the Soybean sites contained variable amounts of uncultivated
Grassland deemed unsuitable for Soybean production and standing fallow; this
ranged from 8% Grassland at a site in Santana do Livramento county in Rio
Grande do Sul, Brazil, to 17% grassland at a site at Vichadero in Uruguay.
Da Silva et al. found 75 species of Birds living at Cattle ranch sites, of
which 38 species are considered to be South American Grassland species (the
remainder being more generalist species able to survive in a variety of
environments). The Soybean sites were found to host 57 species, including 30
South American Grassland species. Where more than 30 individuals were present
it was deemed possible to measure the comparative population densities between
the two environments; of the 56 species for which this was done 50 species
showed no preference, while five, the Rufous Hornero (Furnarius rufus), Firewood-gatherer (Anumbius annumbi), Great Kiskadee (Pitangus sulphuratus), Grassland Yellow-finch (Sicalis luteola) and Rufous-collared Sparrow (Zonotrichia capensis) favoured Cattle ranchland while one species,
the Eared Dove (Zenaida auriculata),
was present at higher densities in Soybean cultivation sites.
Only five species classified as
Threatened or Near Threatened were observed during the study. The Greater Rhea
(Rhea americana), Burrowing Owl (Athene cunicularia) and Black-and-white
Monjita (Xolmis dominicanus), were
observed on both Cattle ranches and Soybean plantations, whereas the Sedge Wren
(Cistothorus platensis) and
Saffron-cowled Blackbird (Xanthopsar
flavus) were seen only on Cattle ranches.
Sedge Wren (Cistothorus platensis).
Graziela Dotta in da Silva et al. (2015).
The species composition in the
two environments was essentially similar, but the Cattle ranches had a greater
number of Bird species, higher population densities of more species and more Threatened
species than the Soybean plantations, suggesting that this environment was more
favourable. Da Silva et al. note that
this was the first such study of Birdlife in Soybean plantations in South
America, despite the fact that this is the fastest growing form of cultivation
on the continent. They suggest that future studies should seek to incorporate
areas of Soybean cultivation which lack natural Grassland areas, in order to
determine how Birds fare in these areas.
See also…
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