Story and photos by Susan C. Morse
Looking Closely at Bear Nests
Except for the Minnesota black bear that chose to spend the winter hibernating 70 feet up in a bald eagle nest, North American
black bears don’t hang out in tree nests. Rather, the “nests” you
see in the crowns of trees are a byproduct of mast consumption.
Remarkably adept at climbing, a bear will climb a tree and then
stand or sit upon heavier branches while reaching up and pulling
smaller, fruit-laden limbs inward. Broken and bent branches are
placed in piles, concentrating the food so that it may be safely
and comfortably consumed. Female bears are leaner, more agile,
and better built for climbing. Starting as early as July, sows will
climb several different species of trees for their nutritious fruits.
Partaking in tree fruit harvests throughout the summer months,
she can significantly increase her weight – critical fat reserves
that prepare her for hibernation, birthing cubs, and lactation
within her winter den.
Whenever I find an especially large bear nest, or a tree fes-
tooned with several nests, I’ll inspect the trunk carefully, searching
for further evidence. On such trees, I often find claw scars made by
a bigger-footed animal – Mother – accompanied by smaller claw
scar sets created by smaller paws – no doubt her offspring.
Bear nests look like giant squirrel nests. They are most easily
discovered in winter, when the clusters of broken branches, with
leaves still attached to the twigs, contrast with the leafless limbs
surrounding them. The persistent attachment of the nest’s leaves
to their dead branches is interesting. Why haven’t they fallen
off? Plant physiologists have described the “abscission zone” as
a kind of wall between layers of cells just above the leaf attachment. A complex interplay of environmental and biochemical
cues causes the wall’s dissolution in autumn, resulting in the
leaf’s detachment from the twig. Leaves that cling to the bear
nest indicate that the branches were broken in the summer or
early September, before the leaf attachment weakening process
Susan C. Morse is founder and program director of Keeping Track in Huntington,
Clockwise from top: sow bear looking into crown of oak tree;
multiple bear nests; brand new and three-year-old scars on
beech; premolar impression on mountain ash branch.