Outdoor Alaska: Sitka black-tailed deer benefit from decade of mild winters

 Sitka black-tailed deer. Courtesy: US Fish & Wildlife Service
Sitka black-tailed deer. Courtesy: US Fish & Wildlife Service (KTUU)
Published: Dec. 5, 2019 at 5:54 PM AKST
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A decade of mild winters in Southeast Alaska has driven the population on Sitka black-tailed deer to high levels.

"The snow really dictates what they can get to for their forage. Snow usually starts up in the mountains in the early winter and it'll push deer down from the tops of the mountains," said Ross Dorendorf, Area Management Biologist for the areas including Prince of Wales Island and Ketchikan.

He said the phenomenon can be confusing for the casual nature observers who might only encounter the deer at lower elevations.

"Sometimes people think 'oh this is great, there's so many deer, but actually it's kind of a negative sign if there's a lot of snow and you see them on the beach because they're not able to get to the essential forage they need to survive the winter."

Dorendorf says the last winter that was severe enough to cause a die-off in the deer population was around 2008.

The deer population is kept in check by predators and hunters. However, the prevalence of both fluctuates across Southeast Alaska.

The primary predators of Sitka black-tailed deer are wolves and black bears. In the ABC Islands, neither of those predators are present. Although the islands are home to large brown bear populations, Dorendorf says they aren't considered a major predator of the Sitka black-tailed deer.

"The key thing is allowing enough opportunity for hunters to make a decrease in the population that it takes animals that would have died anyways in a harsh winter," Dorendorf said. "And it can be difficult to do because hunter harvest as a lot to do with access, so how close you are to a major town where people live, road access, boat access here in Southeast is very important."

The forest landscape that covers Southeast Alaska prevents biologists from being able to get a minimum count of animals in the population. Rather, the Department of Fish & Game relies heavily on hunter harvest to gauge the population.

"Island populations are generally higher than the mainland populations, and it's because of the winters that we have. As you get closer and further into the mainland, the harsher the winters are, the more snow they get and the more persistent that snow is," Dorendorf said.

On the islands, surrounding water moderates the winters.

"When you go out into the islands, it has more of a maritime climate, so it's warmer and they can thrive more, there's more vegetation and habitat for the deer," said Dorendorf.

Deer on islands without an established population of predators have seen the most growth in numbers, but that growth also puts them at greater risk for a large die-off during the next harsh winter or over a succession of harsh winters.

"The biggest driver of deer populations in Southeast Alaska is winter, and with the changing climate we're seeing just, which could easily flip and change in one year and we could have a succession of many hard winters in terms of snowpack," Dorendorf said. "We just haven't seen that for a while, but only time can tell when the next one is going to be coming around."

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