Nine lives won't help to perpetuate a cat species unless the cats manage to reproduce. The decline of wild cheetahs (Acinonyx jubatus), classified as "vulnerable" by the IUCN, led to the coordination of captive breeding programs in zoos and other breeding facilities. And while many know of the trouble that zoos have encouraging pandas to reproduce, fewer people know that zoos often have problems encouraging breeding among captive cheetahs. Zoos see low rates of conception, irregular cycles of estrous among females, and pairs recommended for breeding often simply fail to mate. Inn 2011, only 5.58% of the worldwide captive cheetah population successfully bred. Of 241 facilities that house captive cheetahs, only 33 saw the birth of at least one cheetah cub. Wild cheetahs, on the other hand, have no such problems.
Reproductive physiologists have determined that there are no physiological differences between wild and captive cheetahs, or between breeding and non-breeding captive cheetahs, that could account for the disparity. That is, captivity itself doesn't result in physiological barriers to breeding. Instead, the failure of captive cheetah breeding programs is probably behavioral. In cases like this, it helps to look at management and husbandry practices.
Wild female cheetahs are solitary except when they're caring for their cubs. Males, on the other hand, can be solitary, but are more often found in groups of related males. Pairs of males may be brothers, sharing both a mother and a father, or may be half brothers sharing just one parent. It is thought that, like other big cats, coalitions can maintain control over their territories for longer than can lone cheetahs. And more females are observed in territories controlled by coalitions, thus increasing the possibility of reproduction for each male. If you're a male cheetah, it pays to participate in a coalition.
Most animal welfare laws require that facilities house animals such that they can exhibit their natural behaviors. For cheetah males, this can mean housing them socially, in groups of related individuals. Occasionally, however, due to the requirements of breeding programs, littermates need to be separated and placed in different zoos or breeding centers. What is to become of the separated siblings?
In the wild, lone males have been observed joining pairs of littermates to create larger coalitions. Coalitions formed of three wild cheetahs have always been seen comprised of two littermates and a third unrelated individual. When forced to separate littermates, could zoos encourage the remaining cheetah to join a pre-existing coalition formed of two siblings or half-siblings, just as non-captive cheetahs do?
Researchers from Manchester Metropolitan University and the University of Salford led by graduate student Carly Chadwick took advantage of a natural experiment to answer this question. They conducted 124 hours of observations of four captive male cheetahs at the UK's Chester Zoo, carried out on 23 days over the course of a little more than a year. They published their findings last month in the journal Zoo Biology.
In April 2008, a pair of year-old male siblings, Burba and Singa, arrived at the zoo from the Wadi al Safa Wildlife Centre in Dubai. A month later, another pair of year-old males, half siblings Matrah and Shiraz, came to the zoo from the Sharjah Breeding Centre, also in the United Arab Emirates. Initially, the two pairs were housed separately, in different parts of Chester Zoo's cheetah enclosure. While each pair could see the other through a fence, they never interacted. Then, in December 2008, the gate between the two areas was opened, effectively creating one three-and-a-half square kilometer enclosure for all four cheetahs to share
Impressively, the researchers only observed eleven instances of physical aggression between the pairs while all four cheetahs were housed together - a rate of just 0.06 aggressive behaviors per cheetah per hour! This is actually consistent with data from wild cheetahs, which suggest that aggressive encounters are rare when the groups are evenly matched, and more likely only when one coalition outnumbers the other. Still, there were no instances of affiliative behavior - such as grooming - between unrelated individuals. And the cheetahs were more alert, displaying more vigilance behaviors, when they could see an unrelated male nearby. Despite being housed together, the four cheetahs maintained their smaller coalitions of related pairs.
This represented the first important finding from the study: multiple male coalitions can be housed in a single enclosure, provided the enclosure is large enough to allow unrelated individuals to keep their distance from each other.
Then, in May 2009, one of the coalitions was split up. Shiraz was sent to another zoo for breeding purposes, leaving his half-brother Matrah alone with brothers Burba and Singa. Eventually, Burba and Singa adopted to Matrah into their coalition, just as wild cheetahs had been observed to do. After Shiraz left, the siblings Burba and Singa spent more time in closer proximity to Matrah than they had previously, even though Matrah was unrelated. Over time, Burba and Singa also reduced their vigilance when Matrah was visible. Eventually they even groomed the unrelated male!
The researchers thus demonstrated that unrelated males can be incorporated into coalitions of related cheetahs in captivity, just as often occurs in the wild.
Towards the end of the study period, a female cheetah was brought to Chester Zoo from nearby ZSL Whipsnade Zoo. The data collection for this particular study ended before the female was introduced to the three males. However, Chadwick says that "Matrah has since successfully reproduced with the female and she had a litter in June, 2011."
Was Matrah more reproductively successful because he was incorporated into a coalition? Or might he have sired offspring regardless? In studies like this it is usually impossible to know. But when it comes to cheetah breeding efforts, the birth of a cub is what matters most.
Update:The Chester Zoo has just announced the birth of a second litter of cubs by their female cheetah in June 2013, also fathered by Matrah!
For more on animal social networks:
Chadwick C.L., Rees P.A. & Stevens-Wood B. (2013). Captive-Housed Male Cheetahs Form Naturalistic Coalitions: Measuring Associations and Calculating Chance Encounters
, Zoo Biology, n/a-n/a. DOI: 10.1002/zoo.21085
Header photo via Crocsetal/Wikimedia Commons.