Elizabeth Freeman and Janine Brown, from the Elephant Diagnostic Lab at the Zoo's Conservation and Research Center, are examining how environmental and social factors affect the well-being of African savanna elephants in zoos in order to maximize their reproductive potential.
Yet, the North American population of African savanna elephants (Loxodonta africana) is not self-sustaining (Olson & Wiese 2000), even though recently enhanced breeding efforts have lead to increased pregnancy and birth rates. With restrictions and political concerns associated with importation, zoos must enhance the reproductive success of their elephants to maintain the population.
|The normal ovarian cycle (pink) of elephants lasts about 14-16 weeks. This means that an elephant is typically able to conceive about once every four months. However, some zoo elephants do not cycle (blue) but instead maintain baseline levels of progesterone over time. We are trying to find out why.|
One impediment to reaching this goal, identified by Elephant Diagnostic Lab, is that a third of African and a tenth of Asian elephant females that are hormonally monitored do not exhibit normal estrous cycles (Brown et al. 2004 Survey of the Reproductive Cyclicity Status of Asian and African Elephants in North America) and a female who is not cycling normally cannot conceive. The causes of acyclicity and whether it is strictly a zoo-related problem is not known.
Because acyclicity is more prevalent among African elephants, Freeman and Brown are focusing on that species for now. By discovering whether zoo-related factors contribute to the high rates of ovarian inactivity, they hope to enhance reproductive success and improve zoo management to ensure the continued survival and well-being of African elephants in zoos.
Through the analysis of survey, studbook, and environmental data on 123 elephants—70 cycling, 31 noncycling, and 22 with undetermined status—Freeman and Brown produced a mathematical model of zoo-related factors that may be associated with ovarian acyclicity. Results show that climate and zoo location do not affect normal estrous cycles. African elephants living in cooler climates experience at least the same amount of ovarian activity as those in warmer regions.
Thus, there is no scientific evidence that living in northern climates adversely affects reproductive activity in African elephants. In fact, wild African elephants are known to be highly adaptable to a wide range of temperatures, altitudes, latitudes, and terrains (Sikes 1971). Results also found no specific health or dietary factors among these females that impact estrous cycle dynamics. This provides further evidence of the excellent care zoo elephants are given.
Model results also show that heavier, older, and more socially dominant females that have long-term relationships with their zoo herdmates are more likely to be acyclic. This relationship between acyclicity and social rank among zoo elephants deserves further investigation. In the wild, the largest and oldest female in the family unit is dominant and serves as the matriarch (Archie et al. 2006). Within zoo ‘families’, a single female also acts behaviorally as a matriarch and peace keeper, and our results suggest those females are more likely to be acyclic (Freeman et al. 2004 Examination of the Interrelationships of Behavior, Dominance Status, and Ovarian Activity in Captive Asian and African Elephants).
Rather than being a zoo-related oddity, ovarian acyclicity may be an adaptation of existing evolutionary mechanisms whereby some dominant females dedicate more energy to maintaining the social order of their ‘family’ unit than towards future reproduction.
This notion is supported by demographic studies that show reproductive rates decline among wild elephants with age (Laws et al. 1970; Moss 2001) and as they reach matriarchal status (B. Archie, unpublished data). Natural declines in reproductive success among wild elephants suggest that it may be inevitable that dominant African elephants held in zoos will eventually cease cycling. It just may be occurring at younger ages in zoo females who have never given birth than those observed in the wild. We are currently designing methods to non-invasively monitor ovarian activity in the field to investigate factors that affect ovarian activity of wild elephants and discover whether acyclicity is strictly a zoo-related phenomenon.
Preventing reductions in the zoo elephant population will require creating herd structures that promote reproduction. Although the goal of most zoos is to create multi-generational groups that are more similar to wild families, one intermediate strategy may be to move elephants between zoos to create breeding herds that contain an older female—one past the age of reproduction—who can serve as the noncycling matriarch. This might allow younger and more genetically valuable females to cycle and breed.
An interesting finding of the survey study was that transferring elephants to other zoos did not inhibit normal reproductive cyclicity, and in fact the model suggested it was stimulatory. Thus, creating this type of social environment might help us maximize reproductive potential and lead to the development of a self-sustaining North American African elephant population.
Archie, E. A., Morrison, T. A., Foley, C. A. H., Moss, C. J. & Alberts, S. C. 2006. Dominance rank relationships among wild female African elephants, Loxodonta africana. Animal Behaviour, 71, 117-127.
Brown, J. L., Olson, D., Keele, M. & Freeman, E. W. 2004. Survey of the Reproductive Cyclicity Status of Asian and African Elephants in North America. Zoo Biology, 23, 309-321. pdf
Freeman, E., Wiess, E. & Brown, J. 2004. Examination of the interrelationships of behavior, dominance status, and ovarian activity in captive Asian and African elephants. Zoo Biology, 23, 431-448.
Laws, R. M., Parker, I. S. C. & Johnstone, R. C. B. 1970. Elephants and habitats in North Bunyoro, Uganda. East African Wildlife Journal, 8, 163-180.
Moss, C. J. 2001. The demography of an African elephant (Loxodonta africana) population in Amboseli, Kenya. Journal of Zoology, 255, 145-156.
Olson, D. & Wiese, R. J. 2000. State of the North American African elephant population and projections for the future. Zoo Biology, 19, 311-320.
Sikes, S. K. 1971. The Natural History of the African Elephant. New York: American Elsevier Publishing Company, Inc.