"I would put this spear right in him!" Moma declared, banging his weapon on the ground to emphasize the heartfelt sentiment. Maasai have never been hunters, but they are fierce in their defense of the herd, and they kill a lion or two when circumstances require it.

Moma stuffed the shilling notes deep inside his robe and, morning rounds accomplished, reentered the world of his ancestors: a gaunt figure guiding his herd through another dry winter in a land haunted by lions and hunger. The khaki-clad tourists, meanwhile, popped open the top hatches of their Land Rovers, emerged from the roofs like tank commanders, and rumbled off in a haze of diesel fumes to hunt for other exotic sights.

They would find the wildlife thriving on their safari, much as it does elsewhere in the heart of Serengeti National Park and its companion Ngorongoro Conservation Area, contiguous protected regions comprising more than 8,000 square miles (21,000 square kilometers) of rolling grassland, acacia woodlands, and mist-draped volcanic highlands in northern Tanzania. This area sustains the largest community of migrating ungulates in the world, as well as its greatest concentrations of large predators.

Surveys show the wildebeest population at about 1.2 million, a recent high number for this keystone antelope species, which annually renews the Serengeti's pastures with its massive grazing, trampling, and droppings; the shaggy wildebeest also provides ready prey for lions, hyenas, and other predators. Healthy populations of zebras, numbering more than 200,000, hold steady throughout the region; elephants, which virtually vanished during the ivory-poaching days of the late 1980s, have bounced back, now totaling more than 2,000; black rhinos are stable; lions are on the upswing, numbering 3,500, despite earlier setbacks from disease; populations of impalas, topi, eland, gazelles, giraffes, and Cape buffalo are at healthy levels and rising. The only animals in decline seem to be the wild dog and the warthog. On a continent where much of the wildlife has been wiped out, the picture remains generally favorable in the protected areas.

"The Serengeti itself is in good health," said Christiane Schelten, a program officer with the Frankfurt Zoological Society, which advises the Tanzanian government on conservation. "It's intact, and it seems to be working."