Lions and leopards in the park are particularly elusive and difficult to track, so park officials estimate the population of each group primarily through sightings.
"The decline in the number of large predators in the park has been significant," Okello said.
Hyena numbers have fallen by at least 80 percent, while lions have been depleted by 50 percent, he said. Leopard numbers have also dropped. (Related: "'Sex Tree,' Other Medicinal Plants Near Extinction in Uganda" [August 3, 2007].)
Over the past six months, Okello said, he has spotted only one leopard.
A pride of nine lions has "disappeared completely" in the same period of time, he added. (Related: "Lion Killings Spur Fears of Regional Extinction in Kenya" [May 22, 2006].)
Hyenas, which are easier to track, fell from a population of 50 to 10 in just one year in the northern part of the park.
Queen Elizabeth National Park draws up to 45,000 visitors each year—Queen Elizabeth herself will visit this November.
The park covers 765 square miles (1,981 square kilometers) of largely untouched land and borders two of Uganda's largest lakes, Lake George and Lake Albert.
"It has always been our most popular national park among domestic and foreign tourists," said Lilian Nsubuga, spokesperson for Uganda's Wildlife Authority. Most of the visitors to the park come to see large cats and other carnivores.
"If [large cats] are in very small numbers, it's a big problem for us," Nsubuga said.
"The best thing is for the cattlemen to leave the park," she added.
But the Basongora may have ancestral rights to the land.
Part of the park land did belong to the pastoral group before it was reclaimed by the British colonial government, said Wilson Isingoma, resident district commissioner of Kasese District, where Queen Elizabeth National Park is located.
"The land was taken without adequate compensation or finding an alternative place for these people," Isingoma said. However, he added, the "process is underway" for the government to find a permanent place for the herders to resettle.
But Wilson Okali, chair of the Basongora Group for Justice and Human Rights, said that the reason his community is in the park has little to do with ancestry—it's because they had nowhere else to go.
"We have been appealing to the government for years, but the problem is we don't have any place to occupy," Okali told National Geographic News.
"We don't want to stay in the park, but we don't have any alternatives for places to go." According to Okali, the government has promised the herders land in Uganda's Kasese District. But the herders are waiting until they can harvest their crops to relocate. "We are ready to move," Okali said.
Concerning the poisoning allegations, Okali said: "We have never poisoned any animals."
But even once the herders leave, game warden Okello said, effects of the park's temporary residents may linger for years.
Park veterinarians said diseases such as foot-and-mouth disease—which has already broken out among the cattle—and tuberculosis could be transmitted from livestock to wildlife.
Wildlife are vulnerable because they cannot be vaccinated.
Experts also said that it will take 10 to 20 years for the park predators to return to their original numbers after the herders leave.
"It will take time for us to recover," Okello said.
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