Sizing up the competition

For African wild dogs, catching dinner is one thing. In the presence of lions and hyenas, eating it is quite another.

In June of 1991, my wife, Nancy, and I packed up our belongings in Tanzania's Serengeti National Park and, as hard as it was to leave the packs of dwarf mongooses we had been studying for the past three years, headed south in our fresh, white Land Rover. We had decided to begin a field study of the endangered African wild dog and were hoping to find a large, stable population living in woodlands. Although many people think of these wild dogs as savanna dwellers, they actually fare much better in wooded habitat. And so we had set our sights on the Selous Game Reserve, 17,500 square miles in the southeastern part of the country, where Tanzanian wildlife officers told us the dogs were still relatively numerous.

About the size of Costa Rica, Selous is the largest protected area in all of Africa, but it has not attracted much attention from tourists or ecologists, so we had little idea what to expect. After several days' travel, with a stop at the wildlife division offices in Dar es Salaam to collect final permits and instructions, we arrived at the end of the surfaced road in Kibiti. Late in the day, we reached the northern shore of the Rufiji River and found ourselves creeping along a dwindling pair of ruts with grass growing in the middle. Is this really the road, we wondered. And is the whole place this heavily wooded?

The trees and head-high grass had us worried: wild dogs are so rare that one cannot expect to bump into them by chance, and their patchwork coat of brown, black, and white serves as excellent camouflage.

Our concerns were well founded. The Selous is covered by a mosaic of habitats--everything from open plains to dense, riverine thickets and palm swamps--but it is dominated by miombo, a type of woodland characterized by tall, spreading Brachystegia and Julbernardia trees, which thrive in frequently burned areas. Elsewhere in Africa, miombo woodland can be quite open, but in Selous, a bushy understory cuts the view down to between 20 and 100 yards in most places. Week after frustrating week passed with no sign of the dogs.

Fortunately, this fatiguing work was eased by the delight we took in the beauty of the reserve. We arrived at the beginning of the dry season, which runs from June through November or December and is a time of pleasantly cool nights. (For the rest of the year, Selous is intensely hot and humid.) Our study site was well situated. At its southern edge, a chain of five lakes are connected by the broad, sandy Rufiji River. This belt of water is a year-round home to hippopotamuses, crocodiles, buffalo, and a who's who of shorebirds. A line of rocky hills rises a mile to the east, providing a spectacular view of the surrounding area.

The absence of other researchers working in the reserve was in some ways a handicap, as we had to gather much of the background information for ourselves. But we enjoyed the variety: looking for wild dogs one day, mapping vegetation the next, counting impala fawns the day after that. And in many ways, our isolation and the area's tranquillity were a pleasure. Even along the north bank of the Rufiji River, where antelope congregate in the dry season and tourist traffic is heavier, vehicles were few.

Finally, after five months of searching, our luck turned; in November we found, and soon radio-collared, the first of many wild dog packs. Eventually, we counted more than 100 dogs living in the 1,000-square-mile area we chose as our study site. Now that we were able to keep track of the dogs and follow them around, the real work could begin. One of our goals was learning how these medium-sized (45 to 55 pound) carnivores interact with the much larger hyenas and lions (about 100 and 300 pounds, respectively) with whom they share their wooded habitat.

The ancestor of the African wild dog diverged from the rest of the canid family three to five million years ago, and the species is the only living representative of its genus. Skilled hunters, these dogs owe much of their success to group living. Pack size averages about ten adults and yearlings, plus the pups born each year, but it varies considerably, with packs in Selous ranging from three to fifty-six dogs. The larger packs succeed in more of their hunts, can tackle bigger prey, and generally chase prey for a shorter distance before making a kill. Moreover, large packs often bring down two or more antelope in a single hunt--the record is seven impalas, killed by a pack of more than forty dogs, which promptly bolted down all seven carcasses.

Unfortunately, competence in the hunt is not enough to guarantee a secure place in an ecosystem. Studies carried out in Africa, Europe, and the Americas have begun to reveal the pivotal role large carnivores play in the lives of smaller ones--by competing with them for food, by preying on them, and sometimes both. A good example of this interplay comes from North America, where coyote numbers rose dramatically as humans eradicated the wolf; booming coyote populations, in turn, led to hard times for foxes in some areas. (In Yellowstone National Park, the good times for coyotes were recently upset by the reintroduction of wolves, which have begun to take their toll on local coyotes.) In Patagonia, the culpeo (a South American fox) monopolizes areas with abundant prey, forcing another, smaller fox--known as the gray zorro--to live in the gaps between culpeo territories. In Spain's Coto Donana National Park, Iberian lynx prey on Egyptian mongooses, which consequently avoid areas inhabited by the cats. And in Serengeti National Park, three out of four cheetah cubs are killed by lions and hyenas.