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Wednesday, December 19, 2012
What Keeps a Rhino from Sleeping?
What’s the most common behavior among all animals? Sleep! Yes, everything sleeps from flies to elephants. I think we all know personally how important sleep is to our daily lives. It’s difficult to function without it. And we know that stress can disrupt our sleep. Well, animals are no different.
We have just published a scientific paper on how and when wild black rhinoceroses sleep. It’s difficult to find black rhinos in the wild, let alone ones that are sleeping. So we used silent, digital, infrared “camera traps” to monitor them in the field. The cameras were placed in front of two dust pits in two areas of Addo Elephant National Park, located in the Eastern Cape of South Africa.
People often asked how we knew rhinos were sleeping at those sites. Well, our skilled rhino field technician, Jordana Meyer, could see the body prints. But ask yourself—if you weighed around 3,000 pounds, would you want to sleep on the hard ground? No! These dust pans are soft, kind of like memory-foam mattresses.
The cameras took photos whenever there was movement, such as an ear twitch or the rhino rolling over to switch sides. We found out that black rhinos spent about 90 minutes in recumbent sleep at night. (Our study period probably only covered one of three–four sleep bouts the rhinos had throughout the day and night.)
Did males or females sleep longer? Well, what’s your guess based on your experiences?
The answer is males! Did you guess correctly? Well, there are biological reasons for this phenomenon. Female rhinos in the wild are either cycling, pregnant or lactating, so they need more calories to support offspring development. Meaning they have to eat more. So partners, if you find your wife eating in the middle of night when she’s pregnant, don’t question it!
Interestingly, we also found out that rhinos on the two sides of the park were sleeping different hours. Rhinos on the Addo side were sleeping between 8 p.m. and midnight, but rhinos on the Nyathi side were sleeping between 8 p.m. and 4 a.m. Both were sleeping for approximately 90 minutes, but why the differences?
Well, when we went back into the literature, we found out that adult lions, which are only found on the Addo side, are most active between midnight and 4 a.m. When is an adult rhino at risk to a predator? In recumbent sleep. We can’t be sure this is the reason for the difference, but it is a very interesting coincidence.
Moving forward, we hope to continue our sleep research on Lincoln Park Zoo’s rhinos and expand it to other species as well. In the meantime, be sure to get plenty of sleep!
Rachel Santymire, Ph.D., is director of Lincoln Park Zoo's Davee Center for Epidemiology and Endocrinology. Among other projects, she contributes to black rhino conservation efforts in South Africa's Addo Elephant National Park.
Rachel Santymire, Ph.D.
An endocrinologist in the Davee Center for Epidemiology and Endocrinology, Santymire studies stress and reproduction in Gombe's chipmanzees.
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