Stress believed to suppress fertility
HARARE, Zimbabwe (August 2006)––Zimbabwe Conservation Task Force founder Johnny Rodrigues and Presidential Elephant Conservation Project researcher Sharon Pincott contend that the stress associated with gunfire has actually suppressed elephant fecundity.
This finding, if verified, would contradict other studies showing that wildlife populations tend to increase their fecundity under hunting pressure.
Both coyotes and deer, for example, notoriously raise more young successfully when hunting thins their populations, making more food available to the survivors.
But different mechanisms are at work.
Sporadic vs. intensive shooting
While coyotes are hunted year-round, intensive hunting pressure on coyotes tends to be limited to the spring birthing season for cattle and sheep, and the fall deer hunting season, when deer hunters often shoot coyotes as well.
Deer hunting occurs almost entirely within a rifle season typically lasting only 10 to 14 days. Far fewer hunters participate in the bow hunting and other “special” seasons that precede and follow the rifle season, when gunfire is most frequent.
Intensive shooting in the Zimbabwean elephant study area continued for several years.
Pincott, an Australian, has studied the Presidential Elephants “for more than five years,” Rodrigues e-mailed. The Presidential Elephants are “a clan of more than 400 free-roaming elephants, individually known in more than 20 family groups, so named when President Robert Mugabe decreed them ‘protected’ in 1990, to be a symbol, it was then said, of Zimbabwe’s commitment to responsible wildlife management.
“These habituated elephants can be found on the unfenced Hwange Estate,” Rodrigues said, “bordering Hwange National Park.”
“The home range of the Presidential Elephants was underhandedly taken over by hunters, a situation now thankfully rectified,” Pincott told Rodrigues. “The elephants did, however, endure more than two years of unethical hunting.”
Said Rodrigues, “Elephant conception rates during this period were negatively affected, with elephants coming into estrus up to four times before they eventually conceived.”
Elaborated Pincott, “Female elephants only come into estrus once every three months. Some elephants took another six and even nine months to conceive after the first time I witnessed them in estrus. Some elephants whom I witnessed in estrus and being mated during late 2003 have only recently had their babies, some 31 months later. They endured four sessions with the bulls before becoming pregnant. This differs markedly from elephants whom I witnessed in estrus during 2001 and 2002, before gunfire increased substantially, who had their babies the usual 22 months later.
“Occasionally, at that time, elephants were sighted back in estrus three months after an unsuccessful estrus, but this was not the norm. Certainly there are no previous records of the fertile elephants in this population taking up to nine months to conceive.”
Fertility rose when shooting decreased
Added Rodrigues, “Data collection continues now that the gunfire is better under control, to confirm that conception rates have improved.
“Elephant numbers in Zimbabwe have often been cited as having a negative impact on the numbers of smaller species,” Rodrigues noted, “which are said to be declining, despite scientific studies in neighboring Botswana confirming that the numbers of smaller species there continue to increase, despite their even larger elephant population.
Similar effects on other species?
Concluded Rodrigues, “Gunfire continues, legally, inside of Zimbabwe’s National Parks. Although supposedly limited, this ‘ration hunting’ gunfire has at times been reported to be out of control. Some conservationists are now asking, ‘Is gunfire negatively impacting conception of all wildlife?”
“It is difficult for me to believe that only elephants would be negatively affected,” said Pincott.
The Pincott findings come amid continued debate in South Africa over what to do about alleged elephant overpopulation in Kruger National Park. Some park officials would like to cull the elephants, as was done from 1967 to 1994, and seek Convention on International Trade in Endangered Species permission to sell the elephants’ tusk ivory.
Southern Africa Association for the Advancement of Science president Ian Raper recommends dart-administered non-hormonal contraception. “There are 5,326 female elephants in Kruger,” Raper estimated for Agence France-Presse in 2005, “and it would cost only 1.4 million rand, $208,303 or 178,459 euros annually, to administer the contraceptive, which would work for two years.”
“When people talk about threats to bio-diversity,” Raper added, “it would be well to remember that old bull elephants topple trees, not the females and calves who would be the targets of culling.”
Relatively little has been done to research ways to control bull elephant reproductive behavior, but Walt Disney’s Wild Animal Kingdom and the San Diego Wild Animal Park in 2005 funded Colorado State University veterinary surgery professor Dean Henderickson to experimentally vasectomize several South African wild bull elephants in mid-2005.
“Except on smaller reserves,” Henderickson told Denver Post staff writer Katy Human, “the elephant herds are so big that going in and vasectomizing some will not make enough of a difference fast enough. We’re hoping that once the population has been brought down to a reasonable number, we can help them prevent having to cull again.”
Vasectomizing an elephant is no simple task, Henderickson added. “The approach into the abdomen is very difficult because it’s so hard to find landmarks. If you want to know what it’s like to find a rib in an elephant,” he said, “walk up to a textured wall and try to find a stud by looking.”