Ecology, Behavior and Conservation of Golden Lion Tamarins in Poço das Antas Reserve

James M. Dietz (Univ. of Maryland)
Andrew J. Baker (Philadelphia Zoo)

Field coordinator:
Otávio José Narciso

2000 marked the 17th year of continuous monitoring of the behavior and ecology of golden lion tamarins in Poço das Antas Reserve. This research has been supported by the U.S. National Science Foundation (NSF) since 1987. Data are collected daily by six full-time Brazilian Research Assistants

Data from our studies are recorded in six continuous databases:

  1. Demography and genetic relationships
  2. Behavior and ecology
  3. Group movements and use of space
  4. Morphology and reproduction
  5. Collection of hair and blood for use in research on genetics and disease
  6. Collection of feces for hormonal research.

Following are selected results that became available in 2000:

Inbreeding and inbreeding depression
We found that at least 10% of all tamarin offspring born in Poço das Antas Reserve were inbred at some level. Inbreeding was suspected to have occurred through two routes. First, adult females that had not dispersed from their natal group may have bred with a close relative--usually her presumed father or brother. Second, dispersing individuals entered and bred in groups that contained their relatives or formed new groups comprised of related dispersing individuals. The observed frequency of this type of inbreeding suggests that tamarins do not recognize relatives outside their natal group or do not reject them as mates (Dietz et al., 2000).

Molecular genetic analysis of paternity
Observational data on mating behavior in this population suggest that the modal breeding system for golden lion tamarins is monogamy, even for groups containing more than one adult male. Groups containing two non-natal males comprise about 40% of the population. The degree to which actual paternity is shared between males in polyandrous golden lion tamarin groups remains an important, unresolved, issue.

Anthony DiFiore (Department of Anthropology, New York University) is addressing this question by applying new molecular genetic techniques to tamarin blood and hair samples collected over the past decade in Poço das Antas. Preliminary results identify at least 11 of 152 offspring that possess alleles not found in the mother or putative within-group fathers. Another 13 suspected cases of extra-group paternity are under further investigation.

Fecal hormone analysis
We collected over 900 fecal samples from adult female tamarins. These results suggest that the regulation of reproduction by female callitrichids is sensitive to social status, reproductive value and relatedness to breeding males (French et al., in press).

Sources of variability in female reproductive success
We examined the effects of several variables on the number of live births per breeding season in wild golden lion tamarins. The condition of the female was the only variable to predict successfully the number of live-born infants in the current season. Variables that predicted higher numbers of infants in the first litter of a season were the number of infants born the previous season and the condition of the female. The greater the number of infants born the previous season, the more infants born in the current season. We found no evidence for an age-related reduction in fertility (Bales et al., in press).

Tamarin energy budgets
Kimran Miller, doctoral candidate at U. Maryland collected behavioral and ecological data on eight groups of tamarins with the objective of quantifying and explaining variation in individual energy budgets. Preliminary results show positive correlations between percent time spent feeding on a fruit species and the energy content (calories/g dry matter) of that fruit species, and between time spent feeding and average group size. The latter result may be explained by greater search time for food or variation in territory quality. Further analysis will be necessary to understand these relationships.

Intense predation in Poço das Antas
Until 1997, all suitable habitat in Poço das Antas Reserve was occupied by about 347 golden lion tamarins. Mean group size was 5.6, infant survival was very high and most mortality occurred during dispersal by natal individuals 2-3 years of age. Turnover of breeding individuals was infrequent. Predators occasionally took individual tamarins or pairs, but the first loss of a study group to predators occurred in 1995. One group was lost in 1996, two in 1997, three in 1998, four in 1999 and five in 2000. In summary, predators extirpated all but one of our ca. 15 study groups in the past 3yrs. Typically these events involved predation of several tamarins simultaneously, including one or both reproductive individuals in the group. In most cases new reproductive groups soon colonized these territories, sometimes including survivors from the former group. Some territories have been recolonized as many as three times. For the first time in 17 years areas with appropriate habitat in the reserve do not contain tamarin groups.

By 1999, mean size of study groups had dropped to a low of 3.4. Opportunistic observations of ca. 10 groups that we do not study suggest that group size is small throughout the reserve. The frequency of encounters between study groups and dispersing tamarins has dropped significantly. We estimate the number of tamarins in the reserve at 220. Most of our study groups contain adults with no reproductive experience and 5 of 13 have no helpers other than the breeding pair (Dietz and Baker, unpublished data).

Most of the predation events involving several individuals took place during the night, at or near tamarin sleeping sites. Typically, observers arrived at dawn and found radio collars and tamarin hair, blood, tails and heads scattered within 20m of the den tree. In most cases the opening to the cavity in the tree had been enlarged, either at the base of the tree or through the entry hole used by tamarins. The physical evidence suggests that the predator(s) located the group at night, enlarged the opening to the den and killed the tamarins as they attempted to escape in the dark. In a few cases one or two surviving monkeys were seen nearby the following morning.

We have not witnessed predation at a den site and do not know which predator(s) are responsible for these events. One species that we suspect may be taking tamarins from den trees is the tayra (Mustelidae: Eira barbara). Tayras are omnivores adept at climbing trees and with strong claws capable of excavating a tamarin den. Sam Franklin, graduate student at the University of Maryland, spent the summer in Poço das Antas using "camera traps" set at tamarin den trees to try to photograph the predator. Although he was not successful, he did photograph several other animals at the den sites, suggesting that the technique will ultimately identify the predator.