Finding a responsible method of population control that does not compromise animal welfare is a pressing problem for zoological institutions and conservation breeding programmes. This is exemplified by the conservation breeding programme of the golden-headed lion tamarin, Leontopithecus chrysomelas. The number of golden-headed lion tamarins in captivity is currently being limited by, among other means, the use of contraception. We have conducted a study on the effects of contraceptive methods used in golden-headed lion tamarins. Data were collected through the distribution of a survey. The use of Melengestrol acetate (MGA) implants in females was by far the most widespread contraceptive method. It was very effective in preventing reproduction, provided that females were not pregnant at the time of implantation. Pregnancies that had commenced before MGA implantation were carried to term and resulted in viable infants, as far as noted. However, the degree of reversibility was very low and, if females did conceive after MGA implantation, infant survival was lower than expected. The widespread use of MGA implants in golden-headed lion tamarins (and probably other species) should be seriously reconsidered. Alternative methods of population control should be investigated. Possible options include the use of other contraceptive methods, limiting the number of offspring through natural factors and the use of euthanasia under very strict conditions. Animal welfare implications associated with the use of euthanasia are discussed.

In order to be suitable, a contraceptive method should have little or no effects on social organization or behaviour. In callitrichids, changes in socio-sexual interactions between group members, due to hormonal changes induced by contraception, may have consequences for the reproductive inhibition of offspring in their natal group. This may lead to an increased rate of inbreeding. In this paper we report on the endocrinological and behavioural effects of contraception in golden-headed lion tamarins, using data obtained through a world survey and an observational study. Hormonal analysis of urinary oestrone conjugate levels in melengestrol acetate (MGA)-implanted females confirmed earlier preliminary findings (Van Elsacker et al 1994): MGA implants inhibited reproduction through the suppression of ovulation and regular ovarian cycles in the implanted female, while the occurrence of ovarian cycles in the oldest female offspring of each group was not affected. Sexual interactions between the dominant adults still occurred but underwent temporal changes. Reproductive inhibition in female offspring was maintained. Social interactions between group members altered in a non-consistent way but did not have an impact on the stability of the study groups during the study. In principle, MGA implants do not have a detrimental impact on the behaviour of group members. The suitability of MGA implants from a behavioural point of view depends on the extent to which those involved wish to preserve the entire range of natural behaviours for this species. The behavioural effects of other contraceptive methods are still largely unknown.

In Callitrichid primates, offspring remain in their natal group beyond the age of sexual maturity, increasing the group's inclusive fitness by cooperatively rearing their siblings. Contraception of the dominant female in these groups may alter the associated costs and benefits of this cooperative rearing in such a way that offspring themselves attempt to breed when a period longer than the normal inter-birth interval of one year has elapsed. Contraception of the dominant female may also induce changes in socio-sexual interactions between group members, which can lead to increased aggression after a short period. In this study, we investigated the occurrence of aggression in 16 captive groups of golden-headed lion tamarins (Leontopithecus chrysomelas) under three conditions: 1) no contraception used; 2) contraception used and offspring younger than one year present within the group; and 3) contraception used and all offspring in the group older than one year. We found that the probability of aggression occurring in the groups was best predicted by logistic regression models containing the factors ‘group size ‘ and ‘overall proportion of males ‘ or ‘number of sons ‘. Aggression was more likely in larger groups with a high proportion of males or a large number of sons. This effect was significantly stronger for groups in which all offspring were older than one year. Absence of dispersal opportunities and differences in male and female reproductive strategies may explain the observed patterns. The increased instability of large non-breeding groups presents a problem when using long-term contraceptive methods and should be taken into account when making decisions on the most suitable population-control procedures.

Determining habitat requirements for threatened primates is critical to implementing conservation strategies, and plans incorporating metapopulation structure require understanding the potential of available habitats to serve as corridors. We examined how three groups of golden-headed lion tamarins Leontopithecus chrysomelas in Southern Bahia, Brazil, used mature, swamp, secondary and shade cocoa (cabruca) forests. Unlike callitrichids that show affinities for degraded forest, Leontopithecus species are presumed to depend on primary or mature forests for sleeping sites in tree holes and epiphytic bromeliads for animal prey. In this study we quantified resource availability within each habitat, compared the proportion of time spent in each habitat to that based on availability, investigated preferences for sleeping site selection, and determined how golden-headed lion tamarins allocated time to foraging behaviour in different habitats. Each group preferred to range in certain habitats during the day, yet patterns were not consistent across groups. In contrast, all groups preferred to sleep in mature or cabruca forest. Golden-headed lion tamarins spent a greater proportion of time foraging and eating fruits, flowers and nectar in cabruca than in mature or secondary forests. Although the extent to which secondary and cabruca forests can completely sustain breeding groups is unresolved, we conclude that both habitats would make suitable corridors for the movement of tamarins between forest fragments, and that the large trees remaining in cabruca are important sources of food and sleeping sites. We suggest that management plans for golden-headed lion tamarins should focus on protecting areas that include access to tall forest, either as mature or cabruca, for the long-term conservation of the species.