Delayed implantation is known mainly from animals that are tractable in the laboratory. How it works in ursids and how they use it to their advantage in highly variable environments is poorly understood. The timing of implantation, and hence that of birth, appears to vary geographically and also among individual females. It is likely dependent on body condition of the female, which in turn depends on a variety of environmental factors. The interaction between environmental and physiological factors that controls timing of birth and onset of lactation is simply not understood. Further research is necessary to understand how global warming and other broad-scale changes in Arctic conditions may affect reproductive processes.
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© Daniel J. Cox/NaturalExposures.com
Geoff York, USGS biologist and PBI Sustainability Alliance team member, prepares a female bear for a satellite collar. Check out her movements with the PBI Bear Tracker.
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PBI Teen Leadership Camp
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Up Close with Polar Bears
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PBI Maternal Den Study: Triplets!
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Polar Bear Maternity Dens
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Alyssa McCall: Adaptations
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Bear Alert Program: Relocations
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Churchill, Canada's Polar Bear Alert Program
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Clash of the Polar Titans
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Climate Change & Polar Bears: Dr. Andrew Derocher
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Climate Myths: 70's Ice Age Theory
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Dr. Andrew Derocher: Changes I've Seen
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Dr. Steve Amstrup: Bears in 50 Years?
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Fur or Blubber: What Keeps Polar Bears Warm?
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Hope for Polar Bears
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How Do Polar Bears Use Blubber?
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Journey Across Broken Ice
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Maternal Den Study on Alaska's North Slope
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Mothers & Cubs
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Polar Bear Birth & Survival Rates
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Polar Bear Myths & Facts
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Polar Bear Senses
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Polar Bear Social Behavior
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Polar Bears Crossing Thin Ice
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Polar Bears Mess with Cameras
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Steve Amstrup - Four Ice Eco-Regions
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The Polar Bear Song
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Threats to Denning Habitat on Hudson Bay
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Walking Hibernation
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Zoo Diets vs. Wild Diets
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Zoo Play
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Polar Nirvana
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Role of Zoos in Conservation
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Tundra Buggy One: Behind the Scenes
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Field studies track how the bears are faring.
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This polar bear waits patiently for a seal dinner.
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The landscape is dramatic and achingly beautiful.
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Scientists study how the bears are responding to sea ice loss.
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A cub nurses after waking from a nap. Late freeze-ups are energetically expensive for mother bears, who rely on their fat reserves to sustain themselves and their young. Photo by Julene Reed. November 15, 2011.
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A map of satellite-collared polar bears on Western Hudson Bay polar bears shows they're back on the ice at last. Photo copyright Daniel J. Cox/Natural Exposures. December 12, 2011.
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A polar bear conserves energy by napping on the sea ice beginning to form along the coast of Hudson Bay. Photo by Henry Harrison. November 14, 2011.
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A polar bear mother and cub snuggle together while waiting for freeze-up. This image is a screenshot from our Polar Bear Cam yesterday. November 12, 2011.
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A remnant patch of snow provides a good spot for a morning stretch. Unusually warm weather has melted earlier snow and left most of the tundra brown. Photo by Kevin Middel. November 1, 2011.
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A Tundra Buggy heads out to a prime bear-gathering spot so the crew can erect one of the cameras used in this year's Polar Bear Cam. October 16, 2011.
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A wistful-looking polar bear waits along the shore of Hudson Bay, with no ice in sight. October 14, 2011.
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A young, thin bear looks out over the coastline, waiting for freeze-up. Photo by Randy Kokesch. November 11, 2011.
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An arctic hare in winter white is easy to spot on the still-brown tundra. It's highly unusual to have no snow on Halloween. Photo by Henry Harrison. October 31, 2011.
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As if celebrating the first snowfall of the season, a polar bear rolls in the snow. October 19, 2011.
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Bathed in sunlight, a curious polar bear checks out a Tundra Buggy. Photo by Kevin Middel. October 27, 2011.
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By this time of year in the 1980s, the bears would already be out on the ice hunting seals. Photo by Randy Kokesch. November 9, 2011.
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Churchill's Polar Bear Alert Hotline has already received more than 200 calls this year. October 15, 2011.
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Conservation officers prepare to relocate a polar bear from Churchill to the coast of north of town. They've handled a record number of bears to date. Photo by Shari Burnett. November 13, 2011.
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Freeze-up is underway and the bears are heading onto the sea ice, ready to hunt seals after fasting for more than four months. Photo by Kassie Siegel. November 22, 2011.
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Most of the tundra ponds are now frozen and several bears are padding across that ice, perhaps because it's the only ice around. Photo by Randy Kokesch. November 8, 2011.
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Northern lights ripple across the sky above the Tundra Buggy Lodge--the"dance of the spirits" to some native peoples. Photo by Kevin Middel. October 30, 2011.
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Now that cold and snow have arrived in Churchill, the polar bears are more active. Photo by Kristin Dantagnan. November 5, 2011.
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On top of the world: Tim Sears and BJ Kirschhoffer install the main Polar Bear Cam on Tundra Buggy One. October 18, 2011.
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Peaceful moment: A polar bear takes a long nap on the tundra, sheltered from the wind by willow trees. October 20, 2011.
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Polar bears take shelter in the willows during bad weather, waiting out the storm. Photo by Craig Taylor. November 19, 2011.
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Saturday Sleep-in: While waiting for freeze-up, polar bears spend much of their time resting to conserve energy. Photo by Craig Taylor. October 22, 2011.
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South winds over the past week have driven the sea ice away from shore, forcing most of Churchill's polar bears back on land. Old, thin bears like this one may not make it. Photo copyright Daniel J. Cox. December 1, 2011.
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The data is important in a warming Arctic.
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The first bear spotted by our Keeper Leadership Camp students, photo by Victor Alm. October 13, 2011.
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The first ice on Hudson Bay forms near Churchill, Manitoba, each fall--attracting polar bears, who need a platform of ice to hunt seals. Graphic by John Tagney. October 23, 2011.
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The Polar Bear Cam captured an exciting scene yesterday: a wolverine chased by a polar bear. Photo by Kevin Middel. October 28, 2011.
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This fat, healthy male was photographed in the early '80s by PBI's founder, Dan Guravich. Churchill's bears are noticeably thinner now and the population has declined by 22%. November 2, 2011.
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Three of our Tundra Connections panelists take a moment to enjoy bear-watching from a Tundra Buggy. Photo by Henry Harrison. November 7, 2011.
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Two male bears spar on the tundra. With colder weather, the bears are more active. Photo by Craig Taylor. November 20, 2011.
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Two male bears touch noses before beginning a sparring session. Actual conditions today are very blustery, with low visibility. Photo by Julene Reed. November 18, 2011.
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Two polar bears snack on kelp along the coast. The kelp doesn't have nutritional value: scientists believe the bears eat it to pass the time. October 21, 2011.
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Two polar bears spar on the tundra following a lightfall snowfall. Colder temperatures have led to more polar bear activity. Photo by Rebecca Noblin. November 3, 2011.
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What a beautiful sight! Churchill's polar bears are heading onto the sea ice to hunt seals. Photo by Craig Taylor. November 21, 2011.
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With no access to seals for weeks to come, a polar bear takes a break from gnawing a bone she found on the tundra. Photo by Kevin Middel. October 29, 2011.
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With no sea ice yet in sight, a polar bear waits patiently in the willows. Photo by Randy Kokesch. November 6, 2011.
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Yesterday, travelers were treated to the rare sight of a gyrfalcon on the tundra. Photo by Julene Reed. November 10, 2011.
Frontiers North's Tundra Buggy Adventure supports PBI by donating nights on its Tundra Buggy Lodge.
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