For the first time ever, zoos will have access to the most comprehensive information about female African lion reproduction as the result of an eight-year study from the Smithsonian Conservation Biology Institute (SCBI) and partners. The findings were published Tuesday, Oct. 13, in the scientific journal PLOS ONE, and should lead to a more stable population under human care.

Maintaining a healthy population of any species requires a basic understanding of their reproductive biology, said Sarah Putman, lead author of the paper and a technician in the endocrinology lab at SCBI. The lion reproductive cycle has been a mystery for many years, but now we have a baseline for what hormone levels should look like and how to diagnose fertility problems in animals that are not following those patterns.

From 2004 to 2014, 19 zoos, including the Smithsonian's National Zoo, provided SCBI with fecal samples from 38 female lions, ranging in age from 0.9 to 13.9 years. Using those samples, researchers from SCBI were able to determine the length of pregnancy for a lion, the hormone pattern that confirms pregnancy or non-pregnancy, the average age that lions begin their reproductive cycle and the associated body weight, and the length of effectiveness of specific contraceptives.

SCBI has a long history of developing and using these non-invasive hormone monitoring techniques to better understand a number of species, said Budhan Pukazhenthi, a reproductive physiologist at SCBI, co-author on the paper and reproductive advisor for the Association of Zoos and Aquariums' African Lion Species Survival Plan (SSP). When zookeepers were struggling to breed lions and the problem was presented to us, our experience made SCBI best-suited to conduct this study with partner support and enthusiasm from animal care staff.

Historically lions had been easy to breed compared to other great cats, most of which are solitary. In 1994, the SSP put a moratorium on lion breeding after a boom in the population. Once that moratorium was lifted in 1999, however, scientists were baffled by a shortage of births. This kind of boom and bust cycle should be prevented with the results of this study. SCBI scientists are also finalizing a similar baseline study for male African lion reproduction.

The next step in the research is to develop artificial insemination techniques for lions as a management tool, in addition to banking frozen sperm from male lions to preserve genes that could later help strengthen the health of or grow the population, Pukazhenthi said.

Additional authors on this paper are Janine Brown and Nicole Boisseau from SCBI; Ashley Franklin from Point Defiance Zoo and Aquarium; Emily Schneider from Shady Grove Fertility; and Cheryl Asa from the AZA Wildlife Contraception Center (Saint Louis Zoo).