Timothy H. Heaton
Biologist and caver Steve Lewis, being familiar with the prevailing consensus about the biogeography of coastal Alaska, was willing to bet that the "fossils" were no more than a few hundred years old. A 1965 paper by biologist David Klein had claimed that southeast Alaska was completely overridden by ice 10,000 years ago and that all mammals living there were recent immigrants. El Capitan Cave lies at the bottom of a classic U-shaped glacial valley, so any record of an earlier history would have been eroded away. But Fred had noticed that the black bear remains in the cave were unusually large, which is typical of Ice Age mammals. More importantly, a second, larger species of bear was represented that no longer lives on the island. Emotions were already a bit charged when I arrived, so I avoided jumping to any rash conclusions. I found my caving skills to be in good order after a ten-year "academic hiatus," and soon I joined the previous visitors in marveling at the field of oddly reddened bones that were perfectly preserved without burial. I rushed to take photographs, notes, and measurements before my hands and body froze up, and I collected several bones for radiocarbon dating and left carefully-labeled flagging tape in their place.
It had been obvious to Kevin all along that the bears did not enter the cave by the same route he had, but that a second entrance to the cave once existed at the far end of the bear passage. Several days were spent searching the dense forest slope above for this entrance, to no avail. Then Mark Fritzke provided us with a high-tech method to try: he programmed the cave survey data into his calculator so that as we surveyed our way up the mountainside from the main entrance, the calculator would tell us how far we were in each direction from the end of the bear passage. We followed our compass and tape to "ground zero" but found nothing that looked like a cave. Fortunately (for us) Kevin had left his compass in the bear den and made a solo trip back in to retrieve it. We established a "yelling schedule," and sure enough, the point of contact was only a few yards from where Mark's calculator had led us. We flagged the spot and began making plans for a major excavation the following year.
Preliminary radiocarbon dates of 10,745 years (complete black bear skeleton) and 9,760 years (giant brown bear remains) not only added to the allure of the project, but they won me and Fred a research grant from the National Geographic Society. In July of 1991, with the help of Pete Smith and his chain saw and winch, we managed to remove a root mass and many large rocks that blocked the sealed entrance. After constructing a tent over the hole to keep the rain out, the excavation began. We carefully mapped each bone and kept careful records as we removed them. A Forest Service office was converted into a laboratory where we cleaned, dried, and numbered the specimens. Half a ton of cave sediment was bagged and removed for wet screening, and a pack full was the fee for would-be assistants at the dig. Paul Matheus, wanting to try out his new dry suit, searched the lake at the end of the bone deposit with a garden rake. All in all we found remains of at least four black bears and three brown bears as well as fox, otter, ermine, bat, shrew, various rodents, and many species of fish. The oldest brown bear was dated at 12,295 years before present, showing that the valley glacier melted by that early date.
Remains of two juvenile brown bears were recovered from alpine Blowing in the Wind Cave in 1992, and in 1993 more remains were found in subalpine Bumper Cave by Kevin Allred and Dave Love. I returned to the island in 1994 and excavated Bumper Cave with Dave's help, funded by an NSS research grant. It was a den site much like El Capitan Cave but whose entrance had never been sealed. In order to screen wash sediments at the remote site we set up a gravity feed pressure system using 1000 feet of fire hose fed by a nearby stream. The cave contained the remains of at least nine brown bears (including three juveniles), a caribou, and several voles (tiny rodents) but little else. Radiocarbon dates ranged from 11,640 to 7,205 years old.
Up to this point a pattern had emerged. All fossils recovered were early postglacial in age. Brown bears, which no longer inhabit the island, were found in caves at all elevations while black bears, otters, and fish (from otter scat) were only found in caves near the ocean. Caribou and fox, which no longer inhabit the island or the nearby mainland, were also recovered, showing that species diversity had actually been higher rather than lower in the early postglacial era. These data ran contrary to conventional wisdom, especially the brown bears which are immigrants from Asia and were thought never to have inhabited the southern islands of the Alexander Archipelago. Could colonization of the islands have been easier before the glaciers completely melted and the valleys filled with water? And then there was a theory proposed by certain archaeologists that Ice Age refugia may have existed in the islands, presenting a possible route for early human travel into the Americas. Could large mammals have lived on Prince of Wales Island all along? These were questions we could not yet answer.
The Bumper Cave expedition had been fraught with difficulties. Because of the Fourth of July weekend and subsequent bad weather, we waited nearly a week for a Forest Service helicopter to take us to the cave, and bad weather also forced us to hike out and have our gear and fossils recovered later. During the wait Kevin took me to another cave in which bones had been located. This was On Your Knees Cave located in the extreme northwestern corner of Prince of Wales Island next to Sumner Strait. In this small cave we recovered part of the femur of a large brown bear and a tibia and several toe bones of a black bear as well as remains of otter and fish that are probably recent. The bear bones had been buried in clay and then exposed by stream erosion, but I expected a typical postglacial age. The femur was submitted for radiocarbon dating along with the Bumper Cave remains. Forest Service geologist Jim Baichtal was the first to get the results, and he called me immediately and told me to sit down. The Bumper Cave dates were right where we expected them, but the brown bear from On Your Knees Cave dated to 35,365 years B.P., three times older than any of the others and predating the last glacial maximum! We sent in the black bear tibia for analysis to confirm the old age, and it was dated at 41,600 years B.P.
What were brown bears doing on Prince of Wales Island 35,000 years ago? They didn't reach the lower 48 states until 12,000 years ago, and that was thought to have been by a more inland route. This added weight to the theory of Ice Age coastal refugia, but it didn't prove it. Some independent research was pointing in the same direction, however. Geneticist Gerald Shields and his graduate student Sandra Talbot in Fairbanks compared mitochondrial DNA of living brown bears from throughout Alaska and the Old World. They found that the bears living on Admiralty, Baranof, and Chichagof Islands of the northern Alexander Archipelago are genetically distinct from their mainland counterparts and are more closely related to polar bears than anything else! This suggested long-term isolation, the very thing that coastal refugia would have naturally provided. Genetics and cave fossils were telling the same unexpected story. Archaeologist Jim Dixon, the latest advocate of the coastal migration theory, was elated by these findings. The search was on for fossils dating to the peak of the last Ice Age, about 18,000 years ago, and for human artifacts from the glacial interval.
The short 1995 field season proved no less spectacular than those before it. Kevin Allred, Dave Love, and Jim Baichtal joined me on an excursion to On Your Knees Cave where we removed sediments for screening. Also recovered, from a different part of the cave than the bears, was the jaw and ulna of a small seal. A radiocarbon date of 17,565 years B.P. was obtained on the ulna, suggesting that the area was area was ice-free at the glacial maximum! In another coastal cave our first human artifact was recovered: the tip of a bone spear point associated with two black bear skeletons. Fossils and sediments from these caves are currently under study as plans are made for extensive excavations over the next several years.
The Tongass Caves Project represents a wonderfully productive cooperative effort. As reported in the February 1995 NSS News, Tongass National Forest is providing lodging, food, and other support for NSS cavers willing to assist in finding, mapping, and evaluating caves on the Alaskan islands, particularly in proposed logging units. They are also supporting scientific research in these caves. Geologists, biologists, and archaeologists are working together with cavers, Forest officials, and wildlife photographers to better understand this region and to make the American public more aware of the threats and resources of this region.
Cavers interested in participating in the Tongass Caves Project should contact Steve Lewis, current expedition leader, (907) 479-7257, or Marcel LaPerrier, president of the Glacier Grotto, (907) 225-4094. Space on each summer's expedition is limited.
Slide 1 (#258.124)
Fred Grady at the re-opened "bear entrance" of El Capitan Cave. Vegetation had to be cut and tied back to make room for changing clothes and storing equipment. A tarp was erected over the small vertical entrance to keep the rain out. After the excavation was completed this entrance was sealed up again with large rocks.
Slide 2 (#248.01)
The nearly-complete skeleton of this black bear, scattered on the floor of El Capitan Cave, is what first caught the attention of Kevin Allred and began the research outlined in this article. Remains of a brown (grizzly) bear are also scattered throughout this portion of the cave, the pelvis of which can be seen in the right side of the photo behind the large rock.
Slide 3 (plastic mount)
The nearly-complete skeleton of a brown bear was found in the back of Bumper Cave. It appears to be a female and may be the mother of two cubs who's remains lie nearby. In general, remains further inside each den site are more complete, better preserved, and older than those nearer the entrance. Some bones of this skeleton had fallen down a drain hole in the sediment to the left of the photo and were damaged by rockfall or were washed away. Photo by Dave Love.
Slide 4 (283.192)
This femur of a large brown bear (right) from On Your Knees Cave was radiocarbon dated at 35,365 ñ 800 years old. Farther inside the cave the tibia and toe bones of a black bear (left) were found and dated to 41,600 ñ 1,500 years old. Both had been buried but were exposed by subsequent erosion. The black bear bones were found in small slab of clay clinging to the wall of a narrow crawlway. These fossils predate the peak of the last glaciation.