Biologia reprodutiva de Formicivora erythronotos (Aves: Thamnophilidae)

Abstract

The breeding biology of the Black-hooded Antwren Formicivora erythronotos (Aves: Passeriformes: Thamnophilidae), an endangered species which is endernic to southwestem Rio de Janeiro State, was studied from July 1997 to December 1999 at Angra dos Reis and Paraty. Most of the 31 nests found were placed by the side of trails and roads that were frequently used by people. An intensive monitoring of some nests, totaling about observation 337 hours, allowed that sexual roles on the species' breeding biology were known. Egg laying was preceded by a nuptial display, in which males offered food to their mates. As in other species of the family, male and female Black-hooded Antwrens build the nest, and also take tums incubating the eggs, and brooding and feeding the young. Male's contribution is slightly greater in the latter three activities, and female alone takes charge of noctumal incubation and brooding. Each parent takes care exclusively of one fledgling. The average duration of incubation sessions in this species is much smaller than in other species in the family, while the feeding rate of the young was much greater. These differences may be related to different nest exposure to predation as well as to foraging strategies. Black-hooded Antwren nestlings get heavy faster than nestlings of other species in the family, which may result from the greater feeding rate of the former. The adaptive importance of this accelerated growing is not clear. An "adaptively organized" development, typical of altricial birds, occurred in the Black-hooded Antwren nestlings too. Their body mass, main measurements and development of pterilae can be used to age nestlings of this species quite precisely. The reproductive success was low, in accordance with other tropical birds. Predation was the main cause of losses. Attack by ants seems to be an important cause of mortality for younger nestlings. Parents' efforts to keep nests clean may reduce attraction to these insects. Larvae of Philornis flies have parasitized young. The species' breeding season followed that of the local avifauna, extending mainly from rniddle August to the beginning of February. No individual bird was recorded to be molting and breeding at the sarne time. No difference of food availability has been detected between breeding and molting seasons.