Distributional changes of landbirds species in agroecosystems of

Distributional changes of landbirds species in agroecosystems of central Argentina
Codesido, M.a,b, González-Fischer, C.M.a,b and Bilenca, D.N.a,b
a
Departamento de Ecología, Genética y Evolución, Facultad de Ciencias Exactas y Naturales – Universidad de Buenos
Aires. Intendente Güiraldes 2160 - Ciudad Universitaria - Pabellón II - Cuarto piso. Ciudad Autónoma de Buenos Aires
(C1428EGA), Argentina.
mcodesido@ege.fcen.uba.ar
dbilenca@ege.fcen.uba.ar
cfischer@ege.fcen.uba.ar
b
Consejo Nacional de Investigaciones Científicas y Técnicas - CONICET- Argentina
Key words:agricultural intensification, agroecosystem, grassland birds, pampas, argentina
Introduction
In the Pampas of Central Argentina, land use practices have deeply modified the original land cover of temperate
grasslands in a relatively short period of time (Bilenca and Miñarro 2004).In spite of the many recent studies regarding
the effects of agricultural practices on avifauna in the Pampas, there are no studies comparing changes in bird
assemblages with baseline data.We offer the first quantitative comparative study of actual landbird species distributions
(2006–2008) with those recorded prior to the massive introduction of transgenic soy bean crop at Buenos Aires
province in the pampas of Central Argentina (Narosky and Di Giacomo 1993, hereafter N&DG study).
Materials and methods
Surveys of landbird species were conducted along 18transects covering 23 counties of Buenos Aires province,
Argentina. Each transect was 20 km long, with permanently marked survey points located every one km and was
sampled four times between 2006 and 2008.To allow comparison between our observations and those of the N&DG
study, we used the number of counties in which each species was recorded as an estimate of its present and past
distribution range.To avoid potentially confounding effects due to species rarity, we restricted our comparison study
only to those species previously reported as “abundant” or “common” by the N&DG study.
Results and discussions
Comparisons of distributional ranges showed that 25 species were present in agreater number of counties in the N&DG
study than in our study. On theother hand, 14 species showed their presence in a greater number of counties in ourstudy,
whereas ten species remained unchanged. Grassland bird specialists andwetland specialists are present now in
significantly less number of counties than inthe N&DG study (Wilcoxon matched pairs test, Z7= 2.03, P ≤ 0.05; Z4 =
2.02,P ≤ 0.05, respectively), whereas habitat generalists and woodlandspecialists showed no significant change in their
distributional range. Onaverage, the relative distributional change in the number of counties for grasslandspecialist was
-26%, and was -33% for wetlands specialist.
It should be noted that the N&DG study covered a larger time span than our study, so that the observed reduction in the
distribution of wetland dwellers could merely reflect the shorter supply of temporary water bodies required by these
species during the shorter time span covered by our study. On the other hand, the observed reduction in the distribution
of grassland specialists might reflect the retraction of native grasslands resulting from the increase in the annual crops
area, particularly in the Rolling Pampas, where agricultural expansion has left few remnant grasslands, and three
formerly common grassland specialists (Hymenops perspicillatus, Embernagra platensis and Pseudoleistes virescens)
were no longer detected in our samplings.
Conclusions
A potential regional change in land management towards high-intensity crop-production will most likely result in
distribution retraction of grassland species in the Pampean region. These findings urge the need for conservation actions
of grassland birds in the Pampas, along with continuing monitoring bird programs in the rural landscape.
References
Bilenca, D. N., Miñarro, F. O. 2004. Identificación de áreas valiosas de pastizal (IVPs) en las pampas y campos de
Argentina, Uruguay y sur de Brasil. Fundación Vida Silvestre Argentina, Buenos Aires.
Narosky T., Di Giacomo, A. 1993. Las aves de la provincia de Buenos Aires: Distribución y estatus. Asociación
Ornitológica del Plata, Vázquez Mazzini Editores, L.O.L.A. (Literature of Latin America). Buenos Aires.
162