Natural history notes and conservation of a Saffron-cowled Blackbird Xanthopsar flavus population in the southern coastal plain of Rio Grande do Sul, Brazil

Abstract

Saffron-cowled Blackbird Xanthopsar flavus is a globally threatened icterid of open areas of south-eastern South America. Several sources suggest that the species is declining throughout its range, mainly due to habitat destruction. Between December 1997 and December 1999 we studied a breeding population of X. flavus at the Banhado do Vinte-e-Cinco and Banhado da Mulata area, Rio Grande municipality, Rio Grande do Sul state, Brazil. This population, previously unreported for the state's coastal plain, numbers at least 60 individuals and seems confined to an area of c. 35 km². The area is characterized by Cyperacaea-dominated peat marshes in comparatively higher terrain, covered with sandy, rolling fields. The species was recorded in all months (not necessarily of the same year) except March, and a marked irregularity in flock size was detected. During the non-breeding period, flock size averaged 12.7 individuals (S.D. = 11.7; range = 2-37; n = 11). During the 1997-1998 breeding season (December to January), mean flock size was 25.3 individuals (S.D. = 16.2; range = 16-60; n = 7), while in the 1998-1999 and 1999-2000 breeding seasons, 33 and 4 individuals were recorded respectively. No pronounced discrepancy was found in the size of the largest flocks recorded per season (from 20 to 37 individuals), suggesting that the population is sedentary and that it undertakes only local movements. A nesting colony occupying the same part of the marsh in two successive breeding seasons was composed of six breeding pairs in 1997-1998, with an estimated nesting success of 31.8-36.3% at fledgling time. The species is highly gregarious and sociable, foraging flocks frequently following individuals of Black-and-White Monjita Heteroxolmis dominicana and, to a lesser extent, Yellow-rumped Marshbird Pseudoleistes guirahuro and Brown-and-yellow Marshbird P. virescens. Although habitat loss has been indicated as the main factor for the species' decline, we suggest that habitat perturbation and modification may affect negatively recruitment rates in the species and, theoretically, its overall population size. Furthermore, the conservation of Rio Grande's peat marshes should be regarded a regional priority, in order to preserve threatened birds and a very unusual wetland type.