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Dens - UPDATE September 17, 2014

Aster's den - October 23, 2013Aster's den - October 23, 2013 Are some dens favored over others?

Rock DenRock denRe-use of rock dens by Lily, Donna, and especially June might suggest that these dens are preferred. June used the same rock den in 3 of her last 5 years. But dug dens might get significant re-use, too, if they didn’t collapse during spring melts. Dug dens that have good root structure holding the roof together hold up longer and are sometimes re-used. The den where June gave birth to Pete and George in 2005 held up and was used by Cal in the winter of 2008-2009. The dug den where Lily gave birth to Hope in 2010 was made by another bear some years earlier. Aster reused her dug den when her bad leg made it hard to make a new den. We’ll check that den again this fall to see if she is in it to give birth

Dug denDug denSandy areas where digging is easy have more than their share of dens. Jewel gave birth to Fern and Herbie in such a den in January 2012. That fall, they dug their unusually large 9-foot-long den in sand a half mile away. It is still intact due to good root structure in the roof and is a den we’ll be checking for re-use this fall.

Dug denDug denA study in Tennessee showed hollow trees to have more insulation value and be preferred over other den sites available there. In our area, few trees are big enough for dens, but a big white pine that had been damaged by fire developed a hollow at its base and was used two years in a row. We’ve not checked that den since considering that it would involve a major trip into the Boundary Waters Canoe Area Wilderness to get to it.

Open DenOpen above-ground denUnprotected above-ground dens, which are no more than beds, have been used two years in a row, too, unlikely as that sounds. One of those was used by RC in the fall of 2001 until she was disturbed from it. The next winter, she used the same bed over-winter, giving birth to her first cub in January 2003.

Juliet's brush pile den 2013Juliet's log pile den 2013We’ll be checking to see if Juliet’s log pile den is re-used. The structure is solid. The brush pile where Lily gave birth to Eli and Ellie, the Beary-Go-Round cubs, will not likely be used again as workers piled more brush onto it.

An indication of hibernation coming up was Fern’s heart rate of 68 just now. She is 2 years old, 215 pounds, and could give birth in January. Pregnant females typically den in September. We’ll see what she shows us in spring.

Thank you for all you do.

Lynn Rogers, Biologist, Wildlife Research Institute and North American Bear Center


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