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Carnivores are notoriously difficult to study, yet recently, noninvasive carnivore studies have increased dramatically due to technological and methodological advances, and new analytical analysis techniques. For example, the ability to extract DNA from very small and/or poor quality samples, such as single hairs, and other techniques for assessing hormones from faecal samples have increased the ability to make individual and population-level inferences about carnivores. Increased availability of infrared remote cameras has facilitated large-scale surveys across vast areas, targeting multiple carnivores simultaneously. Today, researchers can estimate population size and survival, as well as historic and current rates of movement across fragmented landscapes, and can measure carnivore stress loads without ever catching, handling, or seeing a single individual animal first-hand. Noninvasive approaches draw from cutting-edge advances in genetics, population biology, biostatistics, endocrinology, and epidemiology. It is an exciting time to study carnivores using noninvasive sampling techniques.

Humans have implicitly understood for centuries that hormones affect behaviour and behaviour can affect hormones. However, until recently, our knowledge of hormone-behaviour interactions derived almost exclusively from research and experimentation on only a handful of laboratory species. Recent advances in noninvasive techniques for measuring hormones have made comparative research on wildlife, including primates, possible. This research provides important insights into human behavioural biology and ecology and evolutionary history. This chapter provides an overview of the key historical and theoretical developments in wild primate behavioural endocrinology; summarizes how primatologists have used noninvasive techniques to monitor hormones in the wild to study the endocrinology of primate reproduction, social relationships, and stress; and reviews important methodological considerations for collecting, processing and analyzing hormones in biological materials, as well as discussing the future directions of the field.

This chapter begins with basic information on the reproductive patterns of carnivores as a background for developing research questions and designing sampling strategies for carnivore studies. It describes female estrus cycle stages along with the associated hormones. The chapter discusses reproductive phenomena that vary among species, such as induced ovulation, pregnancy, delayed implantation, and seasonal and lactational anovulation, as well as characteristic cycle patterns, such as monestrum and polyestrum. It presents an overview of the endocrinology of stress with an emphasis on mechanisms of action of glucocorticoids and the role of social stability in the stress response. This general introduction is followed by more specific information on sample collection, comparing the advantages and disadvantages of blood, urine, faeces, saliva, and hair for endocrine analysis, in addition to the hormones that can be detected in each type of sample. The chapter ends with a brief overview of methods for controlling reproduction, such as contraception or permanent sterilization, along with the possible effects on behaviour and social organization.