Chemical Communication in White Rhinoceroses: Insights from Captivity and the Wild

CRES Associate Director Dr. Ron Swaisgood has been studying the meaning of the olfactory signaling system in rhinoceros species for several years, starting wtih experiments conducted at the San Diego Zoo's Wild Animal Park, and more recently teaming up with researchers Dr. Wayne Linklater, CRES Conservation Research Fellow, and Angela White to study olfactory communcation in wild white rhinoceroses at the iMfolozi Game Reserve, South Africa. Field and captive studies have demonstrated just how important dung and urine are for rhinoceros communication, but what precisely is signaled?

Earlier studies at the Wild Animal Park began to tease out what these scent signals mean to other rhinoceroses. Using a simple but controlled experimental design, dung or urine samples of known origin are placed where rhinos will find them. If the behavioral response differs reliably for different categories of scent, then we know that the rhino's nose is sensitive enough to pick up on chemical differences and, more importantly, that some scents are inherently preferred over others. Among several new findings, these tests show clearly that male rhinos can deterine whether or not a female is in estrus and that all rhinos can recognize odor differences between individulas. A most exciting finding suggests that females may use male dung odors to guide their choice of a mating partner.

Recently in iMfolozi, Dr. Swaisgood and his collaborators capitalized on an opportunity to conduct olfactory discrimination tests on 24 white rhinoceroses held for three months in bomas (small holding pens) before translocation to other reserves. These temporarily captive wild rhinoceroses provided an excellent opportunity to learn more about this emerging picture of sophisticated chemical communication abilities in the species. These discrimination tests show that rhinos can indeed distinguish males in breeding condition from females in breeding condition. In another test, rhinos spent significantly more time investigating the dung of dominant than subordinate males, indicating that physiological differences in males of different status affect the odor chemistry of their dung. This likely plays an important role in male-male competitor assessment as well as female choice. Finally, rhinos discriminated among the odors of females in different reproductive conditions, sniffing estrous female dung the longest and pregnant female dung the shortest amount of time. Males undoubtedly use this information when deciding to distribute their limited time to monitoring and courting only those females that are likely pay off in terms of reproductive opportunity.

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