Bygone Bears of Prince of Wales Island
Alaska's only world-class caves changed category from "Unknown" to "Little Known" less than a decade ago, so both scientists and spelunkers are still finding surprises in the limestone passages beneath Prince of Wales Island. Thanks to Owen Mason of the University of Alaska Museum, who sent me copies of two papers by paleontologists Timothy H. Heaton and Frederick Grady, I now know a little about one of those finds.
The papers were published by the journal Current Research in the Pleistocene (which, despite the promise in its name, does not contain scholarly studies by time travelers to the Ice Age). For five years, the authors report, officials with the Tongass National Forest and cave-loving explorers with the National Speleological Society have been finding and surveying the Prince of Wales caves. In 1990, expedition leader Keith Allred poked into a high passage of the cave called El Capitan, Alaska's largest known cave. There he found the nearly complete skeleton of a long-dead black bear, plus bits and pieces of other bears. Allred also found piles of ground-up fish bones---apparently all that remained of bear seat deposited when the cave's ursine residents were still alive.
The spot was an unlikely one for a bear's den---the exploring cavers were far from El Capitan's entrance when Allred found the bones. He reasoned that another, closer entrance had existed in the far past; after further poking about, he found a rubble-closed passage to the surface, the probable entry used by the bears. Then, prudently, Allred left undisturbed what he'd found. He notified the paleontologists, and guided them to the site during the 1991 field season.
Once in the cave, Heaton and Grady took careful note of the surroundings (steady temperature of 40 degrees Fahrenheit, high humidity, small pond filling the cave about 20 meters back from the original entrance). They also studied the bear bones where they lay, and decided that at least one of the cave's long-dead residents wasn't a black bear. Their original guess was that the oversized bones belonged to a giant short-faced bear, an extinct species.
During the 1992 field season, the team conducted full-scale excavations of the El Capitan bear den, opening the old entrance and recovering the fossil remains. Radiocarbon dating supported the scientists' belief that the bones were old, from animals living about 9700 to more than 12,000 years before the present. Laboratory studies confirmed that more than one species of bear had lived in the cave over the years, but none of the fossilized bones were from a giant short-faced bear. The largest bones---and some of the smaller ones---came from grizzlies. The rest were from black bears, as expected.
What hadn't been expected was that the two species had overlapped on Prince of Wales Island for almost 2000 years. Nowadays only black bears are found on this large lump of the Alexander Archipelago, and the two species rarely coexist on any of the offshore land masses of Southeast. Where they do meet, the larger grizzlies usually dominate and drive off the black bears. Though the remains in the cave indicate that grizzly bears were numerous in the early days, in geological terms, quite soon after the glaciers receded from the island about 14,000 years ago, somehow this time they didn't prevail over their smaller cousins. Nobody knows why; no one has enough evidence yet even to make an intelligent guess.
Well, there are more caves, containing more clues to southeastern Alaska's past, waiting to be studied. Perhaps some answers still lie in the limestone beneath Prince of Wales Island, but it's a surer bet that more questions are yet to be found there.
