INTRODUCTION

Giant pandas are being maintained in captivity largely for the purpose of creating a reproductively viable population that will support conservation of the species in nature. Toward this end, researchers and managers have targeted many aspects of husbandry for improvement through scientific investigations. Among the many priorities is the ability to measure ‘well-being’ and possibly alleviate ‘stress’ imposed by a captive environment. Stress research has been increasingly incorporated into captive wildlife breeding programmes, in part because it is widely believed that small enclosures may not allow animals to execute normal escape and avoidance responses to aversive stimuli. Coping mechanisms may be constrained, thus resulting in stress that can compromise psychological and physiological health, including reproduction (Carlstead & Shepherdson, 2000). Among the many deleterious consequences, stress compromises immune function, reproduction, pregnancy sustainability and maternal care (Munck et al., 1984; Baker et al., 1996; Carlstead, 1996; Moberg & Mench, 2000).

How susceptible is the giant panda to stress imposed by ex situ environments? The charisma of this species causes it to attract large and noisy crowds. Also, giant pandas are commonly held at major institutions that often undertake large construction projects. This chapter deals with the sensitivity of the giant panda to its captive environment. Stress, more than other biological concepts, has limited utility at the population level. In a single species, however, individual animals seem to vary remarkably in response to environmental change.

INTRODUCTION

Increasing breeding success in the giant panda requires a better understanding of its complex reproductive biology. We know that the female is typically mono-oestrus during a breeding season which occurs from February to May (within and outside China). Behavioural and physiological changes associated with pro-oestrus and oestrus last one to two weeks, during which the female exhibits proceptive behaviours, such as scent marking, to advertise her sexual receptivity (Lindburg et al., 2001). During the peri-ovulatory interval, receptive behaviours (e.g. tail-up lordotic posture) climax with copulation generally occurring over a one- to three-day interval. Birthing occurs from June to October with a gestation of 85 to 185 days (Zhu et al., 2001). This unusually wide gestation span is due to the phenomenon of delayed implantation, a varied interval before the conceptus implants in the uterus and begins foetal development. The driving force behind implantation in this species is unknown. The giant panda also experiences pseudopregnancy, whereby the female exhibits behavioural, physiological and hormonal changes similar to pregnancy.

Behavioural and physiological cues associated with both pregnancy and pseudopregnancy include decreased appetite, nest-building and cradling behaviours, vulvar swelling and colouration, mammary gland enlargement and lethargy. Additionally, temporal and quantitative progesterone patterns (tracked by assessing urinary hormone by-products and progestins) are indistinguishable between pregnancy and pseudopregnancy. Therefore, no definitive test currently exists for identifying pregnant from pseudopregnant giant pandas.

Introduction

Studies of behavioral endocrinology provide opportunities to examine the reproductive biology and stress responses of animals. In the case of endangered species, the study of reproductive biology has the two-fold value of contributing to both applied and pure research. In the wild, conservation efforts are enhanced by the assessment of reproductive function and population growth dynamics. It can be used as a diagnostic tool to improve the breeding management plans of captive animal populations. Exchange of information between researchers and managers of captive and wild populations can assist the efforts of both groups (Wildt & Wemmer, 1999). From the standpoint of pure research, studies of reproductive biology help us to understand the evolution of sexual behavior from both proximate and ultimate perspectives, including sex differences in behavior, sexual selection, and the diversity of reproductive mechanisms observed in the animal kingdom. Additionally, studying stress is important because it may affect the reproductive abilities and well-being of individuals which may impact lifetime reproductive success and survivorship.

The reproductive biology of gorillas has been the focus of much research with both captive and wild populations. From an applied perspective, difficulties in captive breeding led to the need for improved understanding of reproductive function. While the lowland gorilla has been kept in captivity since the late 1800s, it was not until 1956 that efforts to have captive gorillas reproduce began and initially the results were poor.