Red squirrel injury to spruce

Last week, we received two different samples comprised of only a half dozen or so cut off terminal ends of a blue spruce branch. Each 3 to 4-inch branch end had been neatly pruned from the tree. The tree owners had found piles of these cut-off ends on the ground around the base of their trees. They sent some to us hoping for some answers. A quick look at the buds revealed the centers had been eaten out. This was the work of our noisy little friends, the red squirrel.

Red squirrels, aka, pine squirrels and chickarees, are native rodents that can be easily identified from other North American tree squirrels by their smaller size, territorial behavior and reddish fur with a white under-belly. Red squirrels aggressively defend their territory from other squirrels. They get annoyed whenever large animals, particularly dogs and people, intrude onto their territory. Anyone who walks the woods recognizes the barks and chatter of an annoyed red squirrel.         Red squirrels have one the widest distributions of all North American squirrels. They occur in Alaska, across Canada to the northeast United States and south through the Appalachians. They also are found in the Rocky Mountains. The diet of these tree squirrels is specialized on the seeds of conifer cones and as such, they live throughout North America wherever conifers are common. There are 25 recognized sub-species of red squirrels. They eat almost anything they can get their little hands on including spruce buds and needles, mushrooms, willow leaves, poplar buds and catkins, flowers and berries and animal material such as bird eggs and bark beetle larvae. In my woodlot, they seem to like walnuts.

Studies in Alaska where white spruce dominates suggest that white spruce seeds comprise over 80 percent of the caloric content of the red squirrels. White spruce cones are harvested by red squirrels and stored in a central cache called a midden. A midden provides the necessary food stores for surviving the winter and reproduction the following spring. Middens of red squirrels that live in predominately hardwood forests are probably comprised of nuts and other available foods. Red squirrel territories may contain only one or several middens. Juvenile red squirrels must acquire a territory and midden prior to their first winter. Juveniles without a midden do not survive their first winter and on average only 22 percent survive to one year of age. Red squirrels do not hibernate and remain active all winter long to defend their territory and middens (and consume vast quantities of bird seed from feeders where these are available.)

One of the more interesting things that have come out of these Alaskan studies is the ongoing struggle between the red squirrel and the white spruce. White spruce trees have developed a defensive strategy called a masting cycle to protect some of their cones from red squirrels. White spruce exhibits 2 to 6 year masting cycles, wherein most years they produce very few seed cones in an attempt to starve the juvenile squirrels, but once every six years or so they produce a superabundant number of cones which essentially overwhelms the red squirrel’s ability to harvest and store all of the cones like they do in years when few cones are produced. The result is that many more cones go uneaten during these mast years while at same time reducing the survivability of the juvenile red squirrels during the off years.  Recent research suggests the red squirrels have adapted to this strategy by developing the ability to tell when a mast year is about to take place. In response, red squirrel females mate a second time and produce an additional batch of pups to take advantage of the large number of seed cones produced.

I don’t really know what to recommend to clients with red squirrel problems, though both Remington and Winchester manufacture products that provide effective red squirrel control and possibly a tasty meal. However, local ordinances regarding the discharge of firearms within city and other municipal boundaries, as well as the legal hunting season for red squirrel must be followed. If you have any other ideas, please contact me.

For more information on red squirrels see:
http://animaldiversity.ummz.umich.edu/site/accounts/pictures/Tamiasciurus_hudsonicus.html
http://www.redsquirrel.msu.edu/index.htm


The squirrels neatly prune the
branch tips from the tree with one
quick bite.
Photo credit: H. Russell, MSU.


A close up of the spruce buds that
were eaten by red squirrels.
Photo credit: H. Russell, MSU


Here are some of the spruce branch tips
that were sent in by clients last week.
Photo credit: H. Russell, MSU

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