Effects of human disturbance on abundance and spatial distribution of lesser rheas.

BELLIS, L. M., J. L. NAVARRO AND M. B. MARTELLA

Hamburg, Alemania.

Congreso; 24th International Ornithological Congress.; 2006

Recent research on spatial ecology has led to consider human disturbances as a new variable for the conservation of threatened species. Lesser Rhea (Rhea pennata pennata), is a flightless herbivorous bird that depends almost exclusively on habitat located on private lands. As privately-owned land management is a potentially important feature that could affect the persistence of wild populations; the aim of this work was to understand the causes that determine the abundance and distribution of lesser rheas in areas with different levels of human disturbance. Fieldwork was conducted from 1998 to 2001 in three sheep ranches of Patagonia (Argentina). Using satellite images and a green index we selected study sites with the same habitat availability: steppe, shrub steppe, shrubland, and vegas, but with different degrees of land subdivision and intensity of human activities. In Loma Blanca (29,000 ha) hunting was actively controlled, there were no free pass roads and sheep density was regulated (1 sheep/4ha); in La Caledonia (20,000 ha) sheep carrying capacity was also controlled; there were free-pass roads and hunting was not actively prohibited; El Remiendo (6,500 ha) had free-pass roads, sheep density was 2-3 ind/4 ha and hunting was not forbidden. Density and spatial distribution of lesser rheas were estimated using the software Distance sampling and CAMRIS GIS, respectively. Rhea abundance was 0.08 ind/km2 in Loma Blanca (2306 ± 513 ind; P < 0.05), 0.03 ind/km2 in La Caledonia (545 ± 26 ind; P > 0.05) and 0.02 ind/km2 in El Remiendo (157 ± 78 ind; P > 0.05). Individuals were distributed in a wide and uniform pattern in the ranch with lowest human pressure (Loma Blanca) whereas in the other sites rheas showed an uneven spatial distribution. Our results suggest that, in Patagonia, human disturbance is an important limiting factor for lesser rhea populations, which stresses the importance to consider land use schemes in conservation efforts.