It's generally accepted that black and brown bears do not get along. Wildlife biologist Kim Titus has seen what happens when a brown bear moves into a stream where black bears are fishing.
"A brown bear shows up and they run," he said.
That would seem to be the case near the Mendenhall Glacier, an area historically known for black bears. Black bears were thick along Steep Creek in September. Sometime in late September or early October two brown bears began fishing the stream.
Uncommon visitors to the Valley
Brown bears not complete strangers to Valley
"Since the time the brown bears started to hang out here, the black bears here have vanished," said Forest Service Naturalist Denise Wolvin, who works at the Mendenhall Glacier Visitor Center near the creek. "I've seen one about three times since they've been here."
The distribution of black bears and brown bears is something of an enigma to biologists. Black bears tend to be forest animals and brown bears tend to prefer more open areas, but habitat alone doesn't determine which species is present.
Areas of Southeast Alaska are dominated almost exclusively by one species or the other, but Titus said bears don't really have a territory. He uses the term home range instead.
"Bears are not territorial in the way wolves are," said Titus. "If you are a wolf in another pack's territory, if they catch you they will kill you."
With black and brown bears, it's more like personal space.
"They may fish and eat salmon off the same rock, but if the brown bear shows up, the black bears will leave or they feed in the middle of the night or whenever the brown bear doesn't want to be there."
Titus, a biologist with the state Department of Fish and Game, has seen black and brown bear interactions on Fish Creek near Hyder, one of the few places where the bears regularly coexist. In nearly all other areas of Southeast, it's one species or the other that predominates.
Black bears are common in the Juneau area. Cowee Creek and Berners Bay are brown-bear country but just across Lynn Canal, from St. James Bay south to Point Couverden, the Chilkat Peninsula almost exclusively has black bears, Titus said.
"The Haines area has brown bears and in Glacier Bay people talk about seeing both," he said.
South of Juneau, Gilbert Bay and Sweetheart Creek are known for brown bears. Further south, Tracy Arm and Endicott Arm are black bear habitat.
"The distribution is perplexing," Titus said.
Scientists suspect one factor is how these animals moved into this region as the glaciers retreated after the last ice age. Some evidence suggests brown bears are an "Old World" species and came across the Bering land bridge from Eurasia, and black bears moved up from North America, the "New World."
Fish and Game biologist Neil Barten said part of the theory is that black bears evolved as a forest species not only do they feel more secure in the brush, they also can climb trees readily, and they are considered more likely to run away than to stand and fight. In comparison, brown bears, which evolved on the plains, in the open, are considered more likely to stand their ground in a confrontation.
The Mendenhall Valley is a border between alpine and flats, and that overlap is appealing to both species, Barten said. The Valley also serves as a funnel to direct bears down from high country. But because there aren't tons of brown bears right around Juneau, Barten said, we don't see interactions very often.
The two species are not completely exclusive, but researchers have found that in areas where brown and black bears overlap, there is some niche partitioning going on, with the brown bears winning out over black bears.
"Perhaps the black bears aren't tolerating the brownies, as much as they are avoiding them as much as possible," Barten said.
Riley Woodford can be reached at firstname.lastname@example.org.