Age structure of two marsupial species in a Brazilian restinga

Abstract

This note is part of a population study of a small mammal assemblage undertaken at Restinga de Barra de Marica, Rio de Janeiro State, Brazil. Here we characterize the age structure and reproductive patterns of two didelphid marsupials: Philander opossum (Linnaeus) and Didelphis aurita (Wied). A capturemark-recapture study was conducted on Restinga Forest, the most complex vegetational type in Barra de Marica (see Araujo & Henriques (1984) and Cerqueira et al. (1990) for a complete description of the area). We established a 4 ha grid with 100 trap stations from July 1988 to July 1990, and this was sampled quarterly, each session consisting of seven trapping-nights. We used Young live traps baited with peanut butter, banana, bacon, rolled oat and manioc slices. Individuals were marked by tail tattooing. Ages were estimated by the dental formulas developed by D'Andrea et al. (1994) and Motta (1988) for Philander opossum and Didelphis aurita, respectively. For the former species the experimental standard error of age estimation is 9.2 days and for D. aurita it is 7.9 days. Age classes were divided according to biological parameters. In P. opossum: class I before weaning, up to 80 days old; class II immature young, 81-175 days old, with no reproductive activity; class III mature young, 176323 days old; class IV adults, individuals of 324 days or more with complete dental development. In D. aurita: class I up to 100 days old; class II 101 to 170 days old; class III 171 to 336 days old; class IV individuals of 337 days or more. The minimum estimated age of a weaned individual of P. opossum was 88 days and for a lactating female 176 days; this agrees with data from captive