Smithsonian National Zoological Park l Friends of the National Zoo



Meeting the Challenge of Preserving Endangered Species

The National Zoo’s Endocrine Research Laboratory evaluates hormones to enhance reproduction and animal well-being of wildlife living in zoos and in nature.

Hormones are the key to reproductive success

Hormones are fundamental to regulating reproductive success and animal health and well-being. The ability to measure reproductive and stress hormone patterns can help determine reproductive status throughout life, physical fitness and physiological responses to change, ranging from the impact of human disturbance to the ability to adapt to a new environment (e.g., reintroduction from captivity into the wild). Most importantly, hormone data can be used to improve animal health and reproductive potential.

Scientists find answers in animal waste

When rare animals fail to breed or thrive, clues generally can be found through hormonal assessments. In the past, monitoring hormones relied on blood sampling after physical restraint or anesthesia, procedures that can be stressful or dangerous for many wildlife species. Hormone byproducts can be measured in urine, feces, and saliva, and collected by animal handlers or field biologists that do not have to disturb the animal’s natural routines.

These "noninvasive" approaches offer extraordinary new opportunities for biologists to understand the fundamental mechanisms associated with endocrine control of general health and reproductive success. Because data can be gleaned from voided urine or feces, reproductive and/or adrenal status can be assessed without the sampling procedures themselves causing stress.

In fact, excreted hormones can be superior to blood data because they represent average values pooled over time, rather than a single point-in time measure.

Among the many advantages, evaluating hormonal metabolites can allow biologists to determine

  • reproductive activity and "stress" status (male and female), including puberty onset, the duration of sexual receptivity (estrus), and the effect of season and aging on reproductive function in captive and free-living animals
  • behavioral cues most reliably predictive of reproductive activities
  • pregnancy diagnosis and birth timing
  • influence of social system (habitats containing single versus multiple animals; single sex versus mixed-sex groups; the impact of immigration or emigration)
  • impact of restraint, anesthesia and translocation practices (radiocollaring)

Exciting new research focuses on using these noninvasive methods to increase our fundamental knowledge about free-living wildlife. Hormone measures are providing important information on reproductive status, but it now is also possible to study the impact of human disturbance or environmental disrupters on animal well being (forestry practices, agriculture, pollutants, toxicants).

Eventually, these techniques may also be important for determining the effectiveness of pre-release conditioning and reintroduction on reproductive performance and animal well-being.

Where do we go from here?

Our understanding of the reproductive physiology of most mammals is rudimentary at best, and detailed knowledge exists for fewer than 100 species. Much less is known about birds, reptiles and amphibians. Although we have begun to utilize zoo-based collections to augment our understanding of reproductive biology, especially through the power of non-invasive hormone monitoring, we have been too slow to extend these studies to free-ranging species.

The past 20 years have witnessed a revolution in the discipline of wildlife endocrinology. There is now the technological capacity to accumulate detailed reproductive databases for literally hundreds of unstudied mammalian and non-mammalian species. Together with non-invasive steroid monitoring, we now have the capability to conduct both basic and applied physiological-endocrine research that can be integrated with other disciplines, including genetics, behavior, nutrition, animal health, ecology and evolution.

The information derived from endocrine studies can satisfy our scientific curiosity, but integrating findings with those of other disciplines is key to defining life history requirements of individuals, populations, and species, as well as complex ecological relationships.

Our goal is to generate more holistic perspectives of how animals reproduce, and to develop an improved understanding of population dynamics, the impacts of human disturbance and the wisdom of undertaking animal translocations and reintroductions.

The emerging discipline of conservation endocrinology can be used to provide wildlife managers and decision-makers with new and valuable information to ensure the survival of viable wildlife populations in nature.