The Breeding of Rufous Horneros (Furnarius rufus)

Abstract

-A partially banded population of 12-13 pairs of Rufous Horneros was studied in Buenos Aires Province, Argentina, during 1970-1976. Territories remained relatively stable during the study. Birds lived in pairs and the pair bond usually lasted for more than one breeding season. Territory sizes ranged from 0.25 ha to about 1 ha. All nesting activities were shared by both sexes. Laying occurred from late August to early December; second broods were attempted in 11 out of 24 nests. Early breeding probably diminished the risks of nest piracy and parasitism by other bird species. Mean clutch size was 3.48 eggs, with individual females showing the whole range of variation (three or four eggs). The incubation period was 16-17 days and the nestling period 24-26 days. Juveniles remained in the parental territories for no less than four months, but they helped occasionally in nest building. Parents opposed this activity. Asynchronous hatching was observed in all the clutches of four eggs; in 9 out of 13 broods of four the younger nestlings died. Nesting success was high, and an average of 2.52 nestlings were reared per clutch. The annual adult mortality was 28.6%, and thus the population probably produced an excess of juveniles. Territorial behavior apparently played an important role in limiting population density. In some aspects of its natural history the Rufous Hornero or Red Ovenbird (Furnarius rufus) is one of the best known furnariids. However, except for the work of Hermann and Meise (1965), little has been published on other aspects of the biology of the species, such as territoriality, pair bonding and longevity. Certain features, such as the complex nests and asynchronous hatching are of interest beyond the species, itself. The permanent territoriality of horneros may play a role in limiting population numbers, and the existence of prolonged family bonds may have some relevance to current sociobiological ideas.