Biologia reprodutiva e organização social de Ramphocelus bresilius (Passeriformes: Emberizidae) na restinga de Barra de Marica, Estado do Rio de Janeiro

AUTOR(ES)
DATA DE PUBLICAÇÃO

1998

RESUMO

The breeding bíology of the Brazilian Tanager Ramphocelus bresilius (Passeriformes: Emberizidae), an endemic species of the east Brazilian coastal region, was studied in 12 hectares of restinga vegetation near Maricá, Rio de Janeiro state, between July 1992 and December 1994. The composition and parentage of the members of four studied groups were determined through bird banding. A total of 167 individuais were aluminumand color-banded. Adults, subadults and juveniles were mist-netted and the nestlings were banded at the nest. During the breeding season groups were composed of up to ten individuais including adult males and females, subadult males and recently fledged juveniles. While subadult males remaineçj in the group for more than one breeding season, females born in the group were not seen any more. The group incorporation of unbanded females suggests that the dispersal behavior is predominant among young females. In order to investigate the influence of environmental factors on R. bresilius reproduction, systematic observations on the availability of ripe fruits of its food plants were made at intervals of two or three weeks from September 1992 to August 1994. Seemingly there was no correlation between fruit production, rainfall and the number of active nests found each year during the study. At Maricá, R. bresilius bred from July to February, which is the same breeding period of other birds at the study area. At the three breeding seasons, 61 active nests were found and studied. The cup-shaped nest was built on bushes and low trees, at an average height of 1.41 m, just leaned on forks or plashed branches. The nests showed three well delimited layers. Their construction began from the outermost layer and they were built in nearly four days. The female alone took charge of nest-building incubation and it was the only one that brooded the young during the first five days of the nestling períod. There was no interval between the ending of building and the start of laying. Clutch size was two or three eggs. Eggs were laid on consecutive days, in the morning. They were pale blue with black spots and dashes. Egg average lenght was 23.2 mm and average width was 17.0 mm. At the laying day its average weight was 3.52 9 (12% of the average weight of adult females, 29.3 g) and at the end of the incubation period, that took nearly 12.5 days, it was 13.6 % lighter. Ali the nestlings in a set hatched in the same day, normally during the morning, with an average weight of 3.15 g. Both sexes fed the nestlings and removed fecal sacs, although the female was more frequent than the male in these activities. The minimum nestling period was nine to ten days and young left the nest before they could fly. This period was shorter than ín other species of the genus. Nine days old nestlingshad an average weight of 20.57 9 (70.8 % of the adult average weight 29.07 g). There was no difference in growth-curve shape for nestlings of two or three clutch sizes. For the most part of the nests, in three of the four groups studied, there were helpers near the nest bearing food to or feeding the nestlings. Parents and other members of the group took care of the young after they left the nest, feeding them and alarming at human approach. Although nests without helpers were not successful, it was not possible to be sure if the helpers improved the chance of brood success, sínce some nests with helpers were not successful either. About one third of ali eggs laid every year, at nests where data for laying and incubation were obtained, developed intó fledged young. The probability of survival of ali active nests, using the Mayfield method, for 1992, 1993 and 1994, was 22.8 %, 19.7 % e 29.4 % respectively. The primary cause of reproductive failure was nestling and egg predation. There was also partial disappearance of nestlings in a brood, possibly by the nest fali or by partial predation of the young

ASSUNTO(S)

mata atlantica restinga reprodução - biologia

ACESSO AO ARTIGO

Documentos Relacionados