RED SQUIRRELS
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    1. •Typically live 2-3 years, but sometimes 5 years.
    2. •After a 35 day pregnancy, female red squirrels can give birth to a single litter with 1-4 pups (usually 2-3) between late March and early May.
    3. •Although the pups can find much of their food on their own when just 40 days old, their mother continues to nurse them until that are ~65 days old.
    4. •A particularly important food source for Isle Royale squirrels is seeds in white spruce cones.  They also eat the buds of spruce branches, mushrooms, invertebrates (e.g., insects and snails), and small vertebrates (e.g., young mice and birds).
    5. •They maintain territories with one or more middens.
    1. Kluane is a wilderness area in southwestern Yukon and the site of a wonderful long-term research project led By Stan Boutin.  Since 1987, Boutin and his colleagues have been observing the lives of hundreds of red squirrels.  It turns out, like wolves and moose, red squirrels are also beautiful and worth knowing better.  Their project is described at http://www.redsquirrel.msu.edu/index.htm.  Much of what has been discovered about Kluane red squirrels would apply to Isle Royale’s red squirrels.
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      Surprisingly, squirrels that delay the timing of their first reproduction tend to produce more offspring over the course of their lives (see graph).  They do it by having larger litter sizes (result not shown here).
 
 
      Although early breeders have greater lifetime reproductive success, it comes at a big cost.  The squirrels that produce the most offspring live shorter lives (see graph).  Late breeders live about 20% longer than early breeders.  
 
 
Context. -- According to the principles of Darwinian evolution, the ultimate measure of success - is lifetime reproductive success (LRS).  That is, the number of offspring an organism produces during its lifetime.  How does a mammal maximize its LRS?  Putting great effort into raising lots of young early in life might be costly to the body, shorten ones life span, and thus prevent reproducing over a long period of time.  However, pacing one’s reproductive effort is no good if you end up dying young from say a predator or some accident.  This
Like squirrels and mice, our modern human lives have been shaped by evolution.  For a fascinating glimpse, check these sites.  You’ll be surprised - guaranteed.
            
These discoveries were made by researchers from the Kluane Red Squirrel Project.  The original research article is: Descamps et al. 2006.  Best squirrels trade a long life for an early reproduction.  Proc. R. Soc. B 273: 2369-2374.  
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Copyright © John A. Vucetich   —  All rights reserved
Red squirrels are an important and interesting part of the Isle Royale community.  If you visit Isle Royale, you will find red squirrels are one of the most conspicuous mammals on the island.  In fact, throughout much of the Northern Hemisphere tree squirrels are conspicuous and easy to observe.  It is good to know about their lives.
Some quick facts about red squirrels                                      
Other kinds of squirrels                                      
The Kluane red squirrel project                                        
A fascinating discovery from the Kluane red squirrel project                                        
Moving on...                                      
Image by: Alexander Yates
If you live in North America, you likely live near several species of tree or ground squirrel.  For information about which live near you, use the outstanding map-based search engine at the Smithsonsian’s Mammal website.
     Red squirrels are able to reproduce when they are one year of age.  However, most squirrels delay the time of their first reproduction (see graph).  Why?  If a squirrel lives for just 3 to 5 years of age, shouldn’t it take advantage of every opportunity to reproduce?  A squirrel might not even live to see its second year.
 
 
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Deer mice, another important member of the Isle Royale community, exhibit an even stranger life-history trade-off.  click here.
 
Human Evolutionary
Ecology Group              
Image by Roger W. Barbour
example is just one of many kinds of trade-offs that affect LRS and define much of why different creatures are the way they are.  Here is the story of a different kind of trade-off, in three short segments...
credit: Smithsonian Institution
juvenile red squirrel
 
Image by Roger W. Barbour