Breeding biology and migratory status of the Warbling Doradito (Pseudocolopteryx flaviventris) nesting in grasslands in its southernmost distribution

The Warbling Doradito (Pseudocolopteryx flaviventris) nests in reedbeds and flooded grasslands near water bodies in central and eastern Argentina. This species is considered resident in large part of its range and migrant in the North and South of its range, but its movements remain poorly understood. We studied the breeding biology and migratory status of the Warbling Doradito in the Biosphere Reserve Parque Atlantico Mar Chiquita (37 degrees 40'S, 57 degrees 23'W; Argentina), at the southernmost limit of its distribution. Warbling Doraditos arrived at the breeding area in October and remained until March. During two breeding seasons (2012-2013, 2013-2014) we studied 35 nests of the Warbling Doradito in Cortaderia selloana grasslands. Mean (+/- SD) clutch size was 2.5 +/- 0.7 eggs (n = 25) and mean incubation period was 17.2 +/- 2.5 days (n = 6). Chicks remained on average 13.2 +/- 1.7 days in the nest (n = 5). The daily survival rate of nests was 0.948 +/- 0.013 (n = 22) for the 2012-2013 breeding season and 0.983 +/- 0.082 (n = 13) for 2013-2014. The probability of nest survival to fledging (mean = 30 days) was 20% for 2012-2013 and 60% for 2013-2014. The main cause of nest failure was predation (92% of failed nests). Nest predation was higher during the incubation period (69%) than during the nestling period (31%). Therefore, the Warbling Doradito has migratory movements in the south of its range, has variable reproductive success between years, and the main cause of nest failure was predation.