Current knowledge on the distribution of Bobolinks (Dolichonyx oryziborus) in South America.

RENFREW, ROSALIND B.; SAAVEDRA, ANA MARIA; DI GIACOMO, ADRIÁN; LOPEZ LANÚS, BERNABE M.; BLANCO, DANIEL; VICKERY, PETER D.

Buenos Aires, Argentina

Congreso; XI Reunión Argentina de Ornitología; 2005

Aves Argentinas - Asociación Ornitológica del Plata

Despite significant declines of Bobolink populations in North America during the past 4 decades, little information exists on the species’ non-breeding ecology in South America. Considered primarily a granivorous, flocking species in during the non-breeding season, bobolinks were historically considered pests in South American rice fields. However, their current status in agricultural habitats is poorly known. Our objectives were to identify wintering areas and abundance and to describe Bobolink habitat use in Bolivia, Paraguay, and Argentina. We conducted roadside surveys in agricultural and natural grasslands in northern Argentina, Paraguay, and Bolivia, from 2001 – 2005. We did not find any large Bobolink concentrations in natural grasslands in Argentina or Paraguay. However, we did find Bobolinks in rice fields in Santa Fe province, Argentina and in Bolivia. In rice fields of central-eastern Santa Fe province bobolinks were abundant when the rice comes into the milk-stage, with a maximum count of 10,000 bobolinks in a field of 50 ha. In Bolivia, we located 8 daytime foraging flocks containing from 100 – 1000 individuals, and 5 night roosts consisting of 150 to 10,000 birds. We found flocks in regions with a high percentage of rice plantations. We observed Bobolinks foraging in rice, adjacent natural grasses, and in soy fields. Bobolinks were not found in soy fields where rice was not abundant, suggesting that they may be feeding only in soy fields located within predominantly rice-growing regions. Continued expansion of agriculture in South America will likely magnify the role of Bobolinks as a potential pest. The mechanisms driving Bobolink winter habitat selection have important conservation implications and warrant further investigation.