Explore is a philanthropic media organization

Mother bear with three cubs in Katmai National Park

Mother bear with three cubs in Katmai National Park

Brown bear, where have you gone?

By “The Artist Formerly Known as Ranger Mike” Fitz

As bear sightings dwindle along Brooks River, the Bear Cams still catch periodic glimpses of single bears and a few females with cubs. However, there’s a dearth of bears at Brooks River compare to peak bear times in July and September. Fall is a season of change, and change comes quickly in Katmai. Where do the Brooks River bears go in the fall? Are they denning right now and are we witnessing the last hurrah for Brooks River bears in 2016?

Information specific to the denning behavior of Brooks River bears is very limited. In the late 1970s, biologist Will Troyer and park staff attempted to track the movements of Brooks River bears during spring, summer, and fall. Troyer was able to find a few radio-collared bears in areas where they likely denned—on the slopes of Mount Katolinat and Mount Kelez, in the vicinity of Ikagluik Creek north of Mount Griggs, and even as far as Wolverine Creek at the base of Kukak and Stellar volcanoes. Curiously, no radio-collared bears at Brooks River were tracked to denning areas on Dumpling Mountain, although bears hibernate there frequently.

In Troyer’s study, he found that female bears moved less far than male bears to their denning sites.

In Troyer’s study, he found that female bears moved less far than male bears to their denning sites.

The study was not able to ascertain when the bears entered their dens. However, from other studies done in Alaska and North America we can surmise that Katmai’s bears enter their dens anytime between mid October and mid December. In Katmai, the denning window may be narrower as studies from Kodiak Island and the southern Alaska Peninsula documented bears entering dens from November to mid December. In general, pregnant females and females with cubs enter the den earlier than single females and males, but that chronology is not universal. Some biologists report no difference in den entrance date based on sex or reproductive status and there are always some male bears that den before all females do.

Bear dens in Katmai are routinely found on steep, well-vegetated slopes with lots of alder and grass. Dens are usually located less than 3000 feet in elevation and average about 1300 feet in elevation.

The entrance to a vacant bear den on Dumpling Mountain. For scale, the hiking poles are 120 cm long.

The entrance to a vacant bear den on Dumpling Mountain. For scale, the hiking poles are 120 cm long.

The migration to a bear’s denning area probably isn’t a quick journey. While bears have the capability to travel long distances in a day or less, they often move slowly toward their denning area, sometimes only covering a few kilometers a day. Bears become lethargic as their physiology begins to switch into hibernation mode (a change that can take weeks). They spend more time resting and sleeping and less time moving. When Brooks River bears leave, they’re probably doing so slowly and resting frequently, not moving in epic marathons of endurance.

Biologists hypothesize that several triggers prompt bears to enter their dens and hibernate: a growing scarcity of food, changing weather, and unconscious physiological changes. We’re seeing the first two on the cams. Bears are catching fewer fish as the last salmon finish spawning and cold temperatures are descending on the region. Fall’s rapid changes are symbolized by bears moving away from Brooks River and into the next phase in their lives.

  • Pam

    Interesting, thanks.

  • PKilborn

    Thanks

  • GABear

    Thanks, Mike. Great info, as always.

  • flyawaygirl

    It does make sense for the bears not to wander for miles to a denning spot and waste necessary fat/energy. It also seems less stressful on a changing body to den in lower elevations. I did find it surprising that the bears near the Katmai region had little denning data but then most places bears chose to live in are difficult to track in the best of conditions.

  • LuvBears

    Thinking about how far they may travel to den, makes me appreciate the bears return to Brooks even more. Your insight always adds to our experience on the cams and especially to our knowledge of the bears. Thanks Mike.

  • ducknet

    A good piece of writing on the Bears of Brooks come winter, heading towords hibernation. Thank you explore.org

    Sleep well Bears. : )

  • lesleezee

    Thank you for the interesting blog article AFKARM. I recall that there are collared bears through the changing tides project. Do the biologists track those bears denning behavior?

    • https://fitznaturalist.com/ Mike Fitz

      Those bears are not tracked to their dens. The collars are removed before then. If biologists cannot sedate a bear to remove its collar in the fall, then a mechanism to release the collar is remotely triggered.

      • lesleezee

        Very interesting, thank you.

  • Birgitt

    Thanks for sharing your insight an knowledge with us. With the dearth of bears, I have been watching old livechats and gleaning info.

    Question for you: Is there hair left behind in the dens or on vegetation at the entrance? And, if so, would it be of sufficient quality (in your opinion) to get DNA from? I.e. might it be possible to use Ranger Saxton’s DNA data to work out which animal occupied a den? Not sure how many dens are discovered each year, but given the difficulty in tracing untagged bears to denning sites, this might be another way to get answers.

    • https://fitznaturalist.com/ Mike Fitz

      Interesting thought. The dens that I’ve examined have been very clean, smelling of earth. I’m sure bears leave some hair behind, but they don’t shed fur when they are in the dens. I don’t know if there would be enough to obtain a DNA sample. Plus, dens aren’t always easy to find. They are much easier to spot from an airplane than on the ground, but extensive hiking is often needed to get to them. Since the DNA project’s main goal is to examine gene flow and local population structure, then other methods to extract DNA samples may be more efficient and cost effective for the project’s objectives.

      • Birgitt

        Thanks for the reply. If there is not enough hair in the dens to get a DNA sample, then the idea is a non-starter. And your point about getting to them on some of those wild mountains is well taken!

        I know that this would not be part of the original intent of the DNA study, but once a database has been created, there are myriad additional things that could be done with it. It might be a matter of; if someone runs across a fresh den, they check for hair samples just in case DNA could be extracted and matched. A slow addition to the current picture.

        Thanks again for all your work on this.

        • https://fitznaturalist.com/ Mike Fitz

          I agree. A family tree of Brooks River bears isn’t the primary goal of the study, but DNA analysis, coupled with observations of known bears along the river, has the potential to provide insight into a whole suite of information no one has ever looked at. If biologists can confirm familial relationships between bears, then perhaps we take take a closer look at certain behaviors, like habituation towards humans, to see if genes could potentially predispose bears to act in specific ways. It’s another way to examine nature vs. nurture.

          • Birgitt

            The possibilities are truly exciting, especially if cam viewers are willing to fund research that interests them. (I certainly am.) Now we are in a brave new world.

            One denning question for you: I have read conflicting information about whether sows nurse cubs besides newborns in the den. I.e. will 128, 409 etc nurse their cubs this winter or are the cubs reliant on fat stores until they emerge from hibernation? And is that why cubs might not survive the winter? Or do we know?

          • https://fitznaturalist.com/ Mike Fitz

            As far as I know, only newborn cubs nurse in the den, since the nutritional needs of spring cubs outpaces the mother’s ability to produce milk by late summer. Even though the metabolism of older cubs, like 128’s and 409’s, is relatively low in the den, they hibernate like adults and survive on stored body fat.

            In terms of energy, milk production is tremendously costly for female bears. Mother bears may be able to sustain those costs for a few months after cubs are born, but the caloric needs of newborn cubs (who only weigh a pound at birth) are a fraction of older brown bear cubs (who weigh 60 lbs or more when they go into the den). It seems unlikely that mother bears can carry enough body fat to sustain themselves and older cubs in the den since caloric needs would be so high. More info on bear milk can be found at http://www.adfg.alaska.gov/index.cfm?adfg=wildlifenews.view_article&articles_id=296

          • Birgitt

            Thanks. And thanks for the great link.

            That makes sense when you consider it. If two 60+ lb cubs are nursing, not only are they draining mom’s fat reserves, their digestive systems are still working and that would make an awful mess in the den.

  • lenoirdenantes

    TY Mike. I wonder if the unusual late autumn weather and the unusual run of salmon has made a difference in the migration to the dens. It seems that the bears are denning just about the same time as the last few years. What do you think about it?

    • https://fitznaturalist.com/ Mike Fitz

      The exact timing of den entrance varies slightly each year and may be triggered by temperature. This was recently documented in a study from central Sweden (https://frontiersinzoology.biomedcentral.com/articles/10.1186/s12983-016-0140-6 ). Since food availability is one of the factors that may influence when bears den, then more salmon may keep them out of dens slightly longer. Even though this year’s salmon run was pretty big, that doesn’t mean salmon are available at Brooks River any longer than normal, because salmon time their spawning fairly precisely. From the limited observations of bears at Brooks River in October, it looks like we saw typical numbers of bears there this year.

  • Jade Bear

    Thanks AFKAR Mike! I’m imagining 132’s den this year but I think in one of the chats they said that she and the cubs might dig several dens close to each other to accommodate each one. Brooks River/Katmai is so beautiful right now!

    • https://fitznaturalist.com/ Mike Fitz

      I don’t recall reading any accounts of cubs denning separately from their mothers before they are weaned and emancipated, so I think they all be in the same den. 132’s den will be huge to accommodate herself and three big 2.5 year-olds.

  • amazed

    I miss them already. Felt a real pang when I saw the above photo. Was wondering about Otis yesterday and sent worried but positive payers about him out to the Universe. We were cautioned about getting “attached” to the bears but that is impossible.

    • Kokamo

      Me too!

    • cpvon

      Me three. It’s December 14th. Hoping to see Otis in the spring.

      • amazed

        Was thinking about him yesterday and hoping he returns to falls next spring. And then there dear old 410…..

        • cpvon

          I don’t know/remember bear 410.
          I love all the bears, but especially Otis.

          • amazed

            410 is the large female (four ton) who fishes at the falls with the big bad males. She is not afraid of humans or anything. She often sleeps on the spit and is the oldest bear at Brooks. Estimated age is 28.

          • cpvon

            Woah! 28!
            So sad she doesn’t have her own name, besides 410.
            She needs a name. :)
            I think I remember her. I do miss all the bears and hope they all survive the winter.

  • Kokamo

    Thank You for this, very informative.

  • CurbGirl

    Thanks Artist Mike!

  • Pandalvr

    Thank you, Mike! Does this mean you won’t be back next year? :-(

  • debra turnbull

    You’re still a great artist I’m sure! Wish you would come back!

  • Greydy

    Thank you for the great blog, and the amazing information on what happens during the fall. I hope all of the “stars” and wannabe and up and coming stars of the falls are resting well. They gave us all so much joy and entertainment watching them interact and grow and grow and grow as they feasted during the spring/summer. Hope you have a wonderful 2017 and that it brings you only great things!