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courting bears (854 and 634)_2_05172015

Brown Bears: Spring Emergence

By Mike Fitz

After a long winter, Katmai rouses in March and April. Daylight lengthens as the sun creeps progressively higher in the sky. Thaw weakens ice on ponds, lakes, and rivers. Flower buds open on willows, monopolizing the attention of queen bumblebees. Migratory songbirds begin to arrive and hibernating animals stir in their dens. Spring is a season of renewal and change. For brown bears especially, it is a time of metabolic, physiologic, and familial transitions.

Katmai’s brown bears greet the oncoming spring while still hibernating. Most are still in their dens throughout March. They’ve eaten nothing, drunk nothing, and have not urinated or defecated in months. Hibernation allows bears to survive winter, but it is a starvation diet that drains most of their fat reserves. Most bears commonly lose one-quarter or more of their fall body weight while in their dens. Maximum daily weight loss for lactating females can approach a half a kilogram per day.

Besides a complete shutdown of their digestive track, the body temperature of hibernating bears drops 8˚-10˚C from their active temperature, 37˚-38˚C, and their heart rate decreases to as few as 10 beats per minute. To become fully active once again, bears need many weeks to slowly shift their physiology from one of rest and energy conservation to fully woke and ready to meet the demands of a new year.

The shift begins long before bears begin to stir. A long-term study on wild brown bears in Sweden found that body temperature began to rise two full months before bears became active and didn’t reach normal levels until ten days after emergence. Bears became active in the den between one and two weeks before emergence, but their heart rate didn’t normalize for a month afterward. The slow heart rate and slightly depressed body temperature after they emerge seems to correspond with a physiological phase described as “walking hibernation” when bears have little or no appetite for up to two weeks after leaving their den. A bear fresh out of the den isn’t yet primed for the active season. It’s still getting ready.

These changes probably initiate sooner in adult male bears, since they have the shortest denning period and typically exit the den before females. Mother bears with cub-of-the-year remain in the den longest and may not emerge until mid-May. Once bears exit the den though, other seasonal demands are just ramping up.

Bear families break up and new ones are made. Mother bears and older cubs separate in spring. Once emancipated from mom, subadult bears must find their own home ranges. Subadult males typically wander much farther than subadult females, sometimes moving dozens of kilometers away. Around this time, single adult bears begin to focus on mating. In mid to late spring, adult females enter estrus and testosterone levels increase in males. Both cycles peak in June, the height of the brown bear mating season.

The first bears we’ll see on bearcam will be far leaner than the fatties of fall. All will have undergone significant biological changes to wake from hibernation. Some will have just experienced emancipation from their mother. Single adults will be primed for the mating season, while mother bears will be focused on feeding and protecting their cubs. In more ways than one, bears in spring illustrate the season’s transitions.


Watch highlights from our bear cam here!

  • Bitmoji App

    Least one to get all the famous bears group and aslo enjoy this emoji es at any time official site http://www.bitmojiapp.org/

    • Juergen

      spamer go away

  • shnzermom

    yeah !!! cant wait to see them

  • Birgitt

    Great post Mike. Factually rich and linguistically lyrical. Many changes to come. Happy spring! Cannot wait to see what it brings.

  • Juergen

    TY Mike great writing as usual!! will be a very intersting season with this many moms and cubs returning and the impact of the bridge building action that seems to be happen this year , hope we can watch at the cams whats going on ….

  • Stacey

    “…the fatties of fall”! :-)

    Thanks for the great post, Mike! Very informative and enjoyable, as always!

  • PennyinMT

    Thank you Mike always enjoy your writing. The big question remains….will 273 send Velcro on his merry way. Hope not!

    • AKdreamer

      I had the same thought while reading the article. It’s hard to imagine him off on his own after witnessing the incredible bond shared with mom.But, he certainly looked capable enough last fall.

    • lenoirdenantes

      I believe that this is the year for Velcro to be emancipated from 273. Only if she does not go into estrus with this be delayed another year and that is a big maybe. I will be crying if Velcro is on his own and watching the cameras every day to make sure he makes it. 273 did a great job of being a sibling to Velcro and teaching him everything he needs to make it on his own.
      Mike, Thank you for the blog entry!

  • http://www.teatrremus.pl/ Kasia

    Yes, they’re coming out and already practising their technical skills. Here’s a Polish cousin of Velcro’s for you dismantling a trap cam in the Carpathians yesterday :-) https://www.facebook.com/NadlesnictwoBaligrodLasyPanstwowe/videos/1299815020094070/


      Incredible! thanks for sharing :)

  • WavestoYou

    Mike, thank you, as always, for sharing your expertise and perspectives. As far as I’m concerned, you could never write too much or too often about brown bears and Katmai….and I’m quite sure I’m not alone in this.
    Can’t wait to see which of them show up and who might have new ones for us to become hopelessly attached to.

  • AKdreamer

    Thank you, Mike! You are such a talented writer and excellent teacher. We are so lucky to have you.

  • https://yellowstoneballpark.wordpress.com/ Ballpark Frank

    Thanks Mike for the educational treatise on ursine spring. I was not aware of the “walking hibernation” state, although it seems like a useful adaptation. While I have seen many bears in a pre-hibernation state in late October and November, I am not sure if I have seen any in a walking hibernation state. (I’m not sure if I would be able to recognize it, based simply on observation. The pre-hibernation bears I have observed were sleepy, sluggish, and bleary-eyed.)

  • Deborah-TX (2014)

    Thanks for putting us in “bear rhythm” Mike

  • Pansy2

    Good timing! I was just going through last year’s pics and wondering how our bruins fared this winter. Thanks Mike!

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    • Juergen

      Spamer post

  • Lea Mulqueen

    Thanks for the great blog post, Mike. When will the cameras go live again?

    • https://fitznaturalist.com/ Mike Fitz

      In the past, the cams have typically gone live in June.

      • Lea Mulqueen

        Thank you.

  • dideebo

    So excited to see our bear family soon !

  • bearvin

    This blog was really informative. I started watching Explore last fall, just in time to catch the tail end of the season. I’m so looking forward to experiencing a brand new season and getting to know these magnificent animals.

    • Stacey

      The summer is SO DIFFERENT from the fall!

      Both wonderful — for completely different reasons!

      Enjoy the bears!

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  • Renée Williams

    I can hardly wait! Last summer was my first time watching explore.org and the bear cam. I have missed them and keep checking for the camera to go live.

  • Stacey

    Thank you for this post, Mike!

    Do you know which bears are featured in the photo at the top of the post?

    To me, it looks like 89 Backpack and 130 Tundra. But it seems more logical for it to be a mother/cub pair.

    Thanks for all you do to help us understand the bears!

  • Genny

    Thank you.

  • Alice BRT

    Can’t wait to see our bears this summer!

  • BearCamAddict

    Thank you for the teaser of Season 2017 of Bear Watch. Can’t wait for the bears!

  • Bonnie Lee

    I miss them so much! I can’t wait to see them again!

  • CarolPgh

    Thanks Mike for whetting our appetite for bear cam season! Can’t wait to see the bears again in June!

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