Nest-site Characteristics and Reproductive Performance of Long-winged Harrier (Circus buffoni) Nesting in Halophytic Grasslands of Argentina.

BÓ MARÍA SUSANA; BIONDI LAURA MARINA; GARCÍA GERMÁN OSCAR; MADRID ENRIQUE

Conferencia; Raptor Research Foundation Annual Conference 2013; 2013

The Long-winged Harrier inhabits open fields, grasslands, savannas, wetlands and marshes in South America. In the southeastern of Argentina Long-Winged Harrier shows a high dependence on halophytic tall grassland for nesting. During six breeding seasons (August-March) we studied the characteristics of nesting site and reproductive performance in this species. The nests (n=85) were built on the ground, and placed below plants of Spartina densiflora (n=43), Cortaderia selloana (n=29) and Juncus acutus (n=13). All nests showed at least one access ramp. The nests associated with different vegetation types differed in the height of the vegetation surrounding the nest-site, the presence of a ceiling-like structure and the number of access ramp. The internal diameter, internal depth of the cup and the height ground-nest edge did not show significant differences between vegetation types. The average clutch size was 3.38±0.89 (N=85) (range: 2-5 eggs). The hatching success (number of egg that hatched versus number of egg laid) was 0.69±0.39 and the breeding success (number of fledglings versus number of nestlings hatched) 0.56±0.40. The productivity was 1.38±1.28 fledglings per pair. Modeling the relationship between the vegetation and nest structure with the reproductive parameters we observed that the elevation from the ground of the nest explained the variability in the productivity of this species. The other reproductive parameters were not explained for the factors tested, the nest elevation can be seen as an important factor underlying breeding success in raptors species that nest on the ground in marshes and humid grasslands, as Long-winged Harrier. That is, for a ground nesting raptor not only the number and diversity of predators present in the breeding area influence the raptor´s offspring survival, but also the building of the nests at a certain height and surrounded by a thick cover are variables that probably affect reproduction.