Welfare implications of captive primate population management: behavioural and psycho-social effects of female-based contraception, oestrus and male removal in hamadryas baboons (Papio hamadryas)

In response to over-population, management actions were taken over a 5-year period to reduce group size and slow the population growth rate of hamadryas baboons at Paignton Zoo Environmental Park. Management involved three planned removals of several individuals and implantation of all adult females with Norplant®, a long-acting contraceptive, expected to be effective for 2-3 years. Possible psycho-social effects of these management strategies were monitored in adult males and females using the rate of occurrence of self-directed behaviour (SDB). SDB was more frequent in males than in females, and in both sexes was significantly more frequent in situations where greater social tension was expected. SDB rates were significantly correlated with overall group size, indicating that the managed reduction in group size was beneficial for the welfare of the remaining group members. Female agonistic interactions were significantly more frequent when they or another female in the harem were in oestrus. However, there was no detectable increase in the rate of SDB of males or females as a result of the contraceptive implants. Despite previous work showing that (a) Norplant® does not stop normal physical and behavioural signs of oestrus and (b) that female hamadryas baboons in oestrus tend to become more aggressive, our results suggest that implantation with Norplant® did not cause a substantial increase in social tension in the group as a whole. However, a small effect could have been masked by the simultaneous and greater effects of changing group size.