Shadow shouldn’t mind if we reveal her true age. She is doing so well having 3 cubs this year. She doesn’t show her age. We’ll have to redo the family tree. We made a mistake on Shadow’s age and now have to admit it. We re-examined the tooth section done in 2002 and found a part of it that showed more annuli. Actually, this tooth is confusing because some of the lines split, but the overall pattern is clear—24 years old in 2011.
For an example of a nice clear tooth that is easy to read, we included the longitudinal section of 26-year-old Midge’s tooth done in 2009. Most bears this old don’t have such easy to read annuli.
What are we looking at? Cementum covers the root like enamel covers the crown. A new layer of cementum is added each year. During the winter when the tooth is growing slowly, it stains darker than in summer when it is growing faster. Since bears are born in the winter, each line (annulus) can be read as a birthday. The root doesn’t close until after the first year, so the first line that goes all the way around the tip of the root marks the bear’s second birthday. When they have cubs, they put a lot of calcium into the milk rather than into the tooth, so there is less cementum added during lactation. So the tooth tells us when they started having cubs and how many litters they raised.
Shadow is still going strong. Midge died of natural causes in November 2009 at the age of 26 ¾.
Out in the woods, Jo’s patch of missing fur is growing back. A short ‘summer coat’ now covers the bald area on her back. Juliet is foraging in perhaps the biggest clover patch we have ever seen. Lily and family are roaming their territory. All the bears are safe but the data is sketchy today with all the rain hampering the GPS units. The rain has stopped. The clouds have parted just enough for the setting sun to light up the tops of the tallest trees. Bodes well for tomorrow.
Thank you for all you do.
—Lynn Rogers and Sue Mansfield, Biologists, Wildlife Research Institute and North American Bear Center