Zina Cave

Although Sitka black-tail deer (a small variety of mule deer, Odocoileus hemionus) are the most commonly-seen of the mammals living on Prince of Wales Island, most of the cave sites excavated have not produced any bones of this species. Deer do not live in caves, and their only predators on the island (bears) do not tend to carry prey to their dens. Deer bones are commonly found in pits (natural traps), but in most cases they appear very recent. Subsequent rock fall probably damages such bones, and the wood and other coarse debris that fills most pits does not promote preservation. To be effectively preserved in a natural trap in the rainforest, an animal must move or be transported away from the accumulation area to a quiet place where the temperature and humidity are fairly constant.

Zina Cave (short for Tlacatzinacantli, the Aztec bat god) is configured so as to be an ideal natural trap for deer and bears. It is located near Staney Creek on central Prince of Wales Island and is the southernmost cave on the island known to contain Pleistocene bones. The cave is entered through a single funnel-type pit (see photo at left), but it actually consists of a complex maze of vertical and horizontal passages. It even contains a raging stream! The unique feature of this cave is that animals were not always killed when they fell in. Instead they wandered about and fell down other shafts before finally meeting their demise. Some of the remains are found in very remote places in the cave, and some probably entered through entrances or passages that are now blocked by debris.

What first brought attention to Zina Cave was the discovery of a deer skeleton with odd antlers by Pete Smith and Jim Baichtal in January of 1998 (see photos below by Baichtal). Baichtal and Dan Monteith collected the skull and other exposed portions of the skeleton and sent them to Dr. Heaton for study. Skeletally the animal is a large male mule deer, but the antlers are unusual. Both have extensive tuberosities around the bases and have posterior basal tines that curve upward. The right antler is broken off above the tuberosities, and the left antler is long and slender and has a single branch near its end. No deer in the extensive Smithsonian collection are very similar to this one. Basal tuberosities occur occasionally in deer with large, many-pointed antlers or with severely-deformed antlers, but they have not been found in conjunction with simple antlers. The Zina deer antler is also unusual in having a long shaft leading to the single branch (most deer antlers branch much closer to the skull). The skeleton was radiocarbon dated to 7,925 years old, which makes it one of the oldest known from Southeast Alaska. Unfortunately no other antlers are known from that early period, so it is uncertain whether this individual was typical or odd in his population. This could be an isolated oddity, or there could have been an unusual population on the island in the early Holocene due to a founder effect.

Dr. Heaton was taken to Zina Cave by Dan Monteith and a cave survey team in the summer of 1998 to examine setting of the various bone deposits and collect further samples. The deer with the odd antlers was found in a horizontal passage below and not far from the cave entrance. It was exposed in a sloping alcove (see photos above) and may have come in through a vertical passage that is now plugged with rocks. In these rocks across the passage from this skeleton was the metacarpal of a different deer that was radiocarbon dated to 5,235 years old. Sediment samples screened from this area did not produce any additional species, but turned up some small bones of the deer. Two more partial deer skeletons were found in a stream-cut passage deeper in the cave, including a female radiocarbon dated to 7,630 years old (see photo at right). Very little water flows through this stream, so the bones were not scattered.

The stream-cut passage mentioned above also contains scattered black bear bones. The four bear bones radiocarbon dated from Zina Cave range from 10,020 to 10,970 years old (far predating the deer remains), so they may have been scattered at a time when more water flowed at this level in the cave. A group of more concentrated bear bones was found in a dry soil passage above the stream. But more deer bones are found at a deeper level. Cavers discovered a small shaft in the floor of a large horizontal passage with air blowing out at high speed. This tight vertical crawlway leads down to a 25-meter-deep pit with a roaring stream at the bottom. Next to the stream at the bottom of this pit is a bear skeleton with every major bone shattered (see photo below at left). It appears that a live bear managed to reach this remote part of the cave then fell down the pit. A bone sample was collected, and it is the oldest of the fossils dated from the cave.

A wet trek down the stream let to another peculiar discovery: a well-preserved bear skull wedged among cobbles against the cave wall at the edge of the stream (see photo below at right). How this skull reach the stream and was washed to this location without being crushed is a mystery. When collected it was found to be very fragile.

All the bear remains of Zina Cave appear to be from black bear (Ursus americanus). Apparently black bears were more abundant than brown bears in the lower elevations away from mountains (Zina Cave is about 200 meters above sea level). As with the other caves discussed thus far, all the remains date to the latest Pleistocene or early Holocene. Since natural traps like Zina Cave and Blowing in the Wind Caves appear to have been effective traps for the last 10,000 years, why do all the bear remains date to the early part of this interval? The same could be asked of the den sites. The answer may reflect a change in population density linked to vegetation changes. Climax coniferous forest provides minimal nutrition for black bears, who seek berries and other plant foods in disturbed areas that have more primary vegetation. At the end of the Ice Age, before the conifers invaded, Southeast Alaska may have been one giant berry patch--supporting an enormous population of black bears! Brown bears are more tied to fish populations, but they prefer open parkland habitat to dense forest. This may explain why they dominated the higher elevations before dying out on Prince of Wales Island.

   
© 2002 by Timothy H. Heaton