Reproductive behaviour, endocrinology and captive breeding of the Malayan Sun bear (Ursus malayanus) : a thesis presented in partial fuflilment of the requirements for the degree of Master of Science in Zoology at Massey University
A better understanding of Sun bear (Ursus malayanus) reproductive biology is essential to implement more effective management of zoo populations. The objective of this study was to document and describe reproductive behaviour, monitor ovarian and testicular cycles, and review approaches to captive breeding. Because Sun bears exhibit no fixed breeding period in captivity, identifying a set of behaviours associated with oestrus, pregnancy and impending parturition are important. During 1997 three male:female pairs at two zoos were studied for periods of up to <10 months. Bears spent the majority of time in solitary behaviours, but oestrus was marked by and an increased rate of affiliative encounters, with females actively soliciting the male, and exhibiting characteristic behaviours including rolling, backward walking and inguinal presentation. Oestrus lasted ~2 weeks, the end being marked by rapid loss of sexual interest, and mutual avoidance. During mid-late gestation females became increasingly intolerant of the male, and altercations were common. Several weeks before term females acted reclusive, and extensive nesting occurred when suitable material was available. Parturition occurred ~3 months after mating, with pseudopregnancy lasting an equivalent period to 'true gestation', and being accompanied by similar behaviour changes and overt physical signs (e.g. mammary development). Separation of the female, provision of a high level of isolation and maintenance of privacy was necessary for successful rearing to occur. Faecal sex steroids were analysed in samples collected from 13 (9 male:4 female) Sun bears housed in zoological parks in North America and New Zealand, over periods of <27 months. Male samples were assayed for testosterone and female samples for oestradiol 17β and progestagens. Testosterone levels were often elevated during mating periods, with peaks frequently accompanying breeding behaviour and copulation. There was no significant effect of season (p>0.05) on testosterone concentrations, which fluctuated throughout the year, with most animals showing sustained increases in androgen excretion at 4-6 month intervals. The mean length of the follicular and luteal phase was 11.2 ± 1.3 days and 93.3 ± 3.0 days, respectively. Increased faecal oestradiol concentrations were associated with the onset of oestrus behaviours and breeding activity; an analysis of endocrine-behaviour data suggests that these behaviours may serve as useful indicators of physiological oestrus. The pattern of oestradiol and progesterone metabolite excretion during pregnancy and pseudopregnancy was similar, indicating that sex steroid monitoring may be of limited use for unequivocal pregnancy diagnosis in ursids. Analysis of studbook data and breeding records from Sun bears in North American and New Zealand zoos revealed that reproduction in these populations is strongly seasonal with the majority (>75%) of births occurring during summer and autumn. A bimodal pattern of reproduction was observed, resulting from sharp peaks in the birth rate during July and October. Findings suggest a correlation between breeding activity and monsoon patterns in this species' native habitat. The factors limiting reproductive success in captive Sun bear populations are not understood. Difficulties confirming pregnancy, coupled with the failure of some zoos to separate potentially pregnant females or implement remote surveillance, reduces reliable statistics for birth or neonate mortality and prevents an investigation of the causes of cub fatality. A review of breeding records from various zoos indicates that standardising approaches to husbandry might also improve Sun bear reproduction in captivity.