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  • How to Eat, but Not be Eaten — Foraging Strategies of Four Urban Squirrel Species

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    Tags: squirrel, squirrels, urban ecology, chipmunks, chipmunk, chicago, chicago wildlife

    Created: 9/19/2014      Updated: 8/9/2016

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    The most common tree squirrels in our region are the grey (Sciurus carolinensis) and the fox (S. niger). Both of these species are scatter hoarders. That is, they bury nuts in random places across the landscape. In contrast, the red squirrel (Tamiasciurus hudsonicus) is a larder hoarder. This means they put all of the food they have gathered in only a few places, like a hollow log or under a rock.

    Grey Squirrel digging in the ground

    Grey squirrel caching

    These two strategies have costs and benefits. A larder hoarder can defend its cache from other squirrels, nut and seed eating birds, and many other species that might rob it of food. Even you may have been scolded by a red squirrel when you inadvertently came too close to its larder. On the other hand, there’s not much a red squirrel can do to deter a determined black bear from raiding the squirrel’s cache. Scatter hoarders don’t have to worry about bears but they do lose a lot of their nuts to competing squirrels and birds, and simply because they can’t find the food once it is buried.

    Fox Squirrel eating in a hole in a tree

    Fox squirrel eating

    These two different foraging methods also result in red squirrels having relatively large territories. You don’t often see lots of red squirrels in the same place at the same time. On the other hand, there are many places where you might see more than a dozen grey squirrels foraging together. 

    Red squirrel on a rock

    Red squirrel

    One thing that does bring lots of squirrels together is bird seed. If seed is buried it either rots or germinates. Either way, it is not very useful to squirrels so, rather than run around caching, as they do with nuts, squirrels will simply sit and eat the seed. The threat of predators and more aggressive squirrels keeps them moving around a little but they are otherwise perfectly happy to sit at the dinner table and eat.

    Chipmunks, though, have a different strategy. They have check pouches. This allows chipmunks to literally stuff their faces full of food, then run back to their burrow, dump the food, and return for more once they think the coast is clear. In this way, they can collect plenty of food to eat, while only exposing themselves to the danger of predation for relatively short amounts of time. The seeds they gather are stored in cool, dry rooms (the same way we store grain) so it stays fresh and nutritious through the winter. This foraging strategy is so successful that chipmunks have become our most common ground squirrel in urban areas.

    Have you ever wondered why you don't see baby squirrels as often as you see adult squirrels? Learn why in this post.

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  • The Art of Taxidermy

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    Tags: taxidermy, squirrel, Chicago Academy of Sciences, specimens, chipmunk

    Created: 6/11/2013      Updated: 8/10/2016

    Earlier this month, I had the privilege of learning the art of taxidermy, or, in layman's terms, skinning an animal and stuffing it with cotton and wire. I have to admit that I thought it would be a much more complicated process involving toxic chemicals and specialized safety equipment. In reality, all you need is a sharp knife (preferably a scalpel) and some borax. So long as you're sure to wash your hands afterwards, you don't even need gloves.

    As we waited for our chipmunks to thaw, we spent some time drawing them, taking a few minutes to learn about the contours of their bodies, where their joints are, and how their fur lies. I learned two things during that time. First, I'm not very good at drawing. Second, I learned what a chipmunk really looks like: how its legs move, how the features of its head sit upon its skull, how the color patterns flow across its body. It was all quite intimate.

    Chipmunk on styrofoam

    After bonding with our specimens, it came time to cut into them, from thigh to thigh, right above the genitals, being careful not to cut through the thin layer of muscle separating us from the rodent's stinking bowels. This was a relief, it hadn't dawned on me that by only collecting the skin, we could leave its mess of organs tucked safely in the package nature made for them.

    This was the only time we cut through the skin, the rest of the cutting we performed was done in between the skin and the muscle, delicately cutting away at the layers of connective tissue. We worked our way from that initial incision to the back knees until we could peel the skin up and over them to fit our scissors around the joint without cutting skin. Then, a bit of pressure, a quick snap, and the femur was separated from the tibia and fibula. We'd come back for those later, it was time for the really fun part. Taxidermists have a special tool for getting the tail out, it almost looks like a pair of wire cutters, but instead of cutting them, it’s designed to hold onto the bones in the tail as you slip off the bushy tail. I don't think I could describe the feeling to you. It sounds rather morbid, I'm sure, but it's really quite delightful, almost like popping the cork on a bottle of sparkling grape fruit juice as a kid on Thanksgiving. You gently apply pressure, anticipation mingled with a tinge of fear, then POP, off it goes.

    Things were pretty straightforward from there to the skull, just like pulling off a sock. It was actually pretty meditative, and there were times when I had to stop and take stock of what I was doing, assuring myself that, "Yes, I really am peeling the skin of a chipmunk, and it really is this interesting." This is around the same time that the museum guests started showing up, many of them school groups. There were two facts which many of the children seemed to have difficulty holding in their heads at the same time: these are real chipmunks, and they are dead. One child, nearly at the point of holding these facts together asked, "Are you're fixing it?" Aside from the confusion, there were some wonderfully refreshing moments when a child grasped what was happening and watched with awe rather than disgust. These are the young scientists our country so desperately needs.

    Group of children reacting to taxidermy demonstration

    Steadily working our way up toward the head, casually chatting amongst ourselves, and enthusiastically sharing with the public what we ourselves had learned only a short while ago, it was time for the difficult part. Not only is the face the cutest part of the chipmunk, it's also the most tenaciously wrapped around the skull. The ears, eyelids, and lips can all easily be disfigured by a hand too quick to finish the job. With the help of our resident expert and trainer, we all managed to keep the cuteness intact.

    At last, the skin was off, and it was on to the next stage. The hollow skin was rubbed with borax to dry it out,  and the fluffy side was turned back to face the right side. Next, wires were cut to replace the bones we had removed. One wire reaching from the tip of the nose to the end of the tail, and two reaching from the front to back paw on either side. The central wire was then wrapped in cotton and molded with twine to approximate the shape and size of the body. Because chipmunk tails are rather thin, about a third of the wire was left bare so that what we ended up with looked a bit like a popsicle. This was then gently pushed back through the incision we had made hours ago, all the way up to the adorable little face we had affectionately drawn at the start of our day. The other two wires were then set into place along the sides of the body, pushing it into the superman pose which it will hold for centuries to come.

    Close up of stuffed chipmunk face

    I thought the final step would be sewing it back up, but I'm glad it wasn't (partly because I found it the most difficult). The final step was "to make the specimen look good." I understand that the real reason for this is scientific, for the sake of our collections, but it allowed me to show my respect for the little critter I had just skinned. Gently combing his fur straight and using pins to get his tail and face aligned was a warm way to end what had been a day of cutting, bone breaking, and stuffing. I found it suiting that the process should begin with careful consideration of the creature in its natural form and end with time spent approximating that form. After all, a quick internet search for "bad taxidermy" might make one shudder to think how embarrassed the ancestors of those creatures would be if they were ever to gain sentience.

    Dennis Baker
    Volunteer

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  • Squirrel Appreciation Day

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    Tags: Squirrel Appreciation Day, squirrel, project squirrel

    Created: 1/21/2013      Updated: 8/10/2016

    Happy Squirrel Appreciation Day! Of course, here at the Nature Museum, we celebrate squirrels every day but the rest of the world officially joins us on the 21st of January, every year. It’s a great occasion to stop and think about all of the fun (and challenges) that squirrels bring to us. At this time of year all of the ground squirrels are sound asleep. They’re hibernating because during winter (at least normal ones) it’s difficult to obtain enough food to stay warm. The famous Punxsutawney Phil will awake from his hibernation shortly to give his input on the coming weather. However, tree squirrels are active all year, subsisting off nuts that they cached during the fall. 

    Squirrel

    For many people, tree squirrels provide the most intense interaction we have with a wild mammal. In the Chicago region, we often take the seemingly-silly antics of tree squirrels for granted. In fact, squirrels could live anywhere that people do and they are found in towns across the country. However, there are many towns, even in Illinois, that don’t have any tree squirrels at all. In other towns there may only be one species while other towns may have two species or more. Why is this? What does it tell us about the ecology of our neighborhoods? Help us answer these questions and celebrate Squirrel Appreciation day at http://projectsquirrel.org/

    Steve Sullivan, Senior Curator of Urban Ecology

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  • Why Don't I Ever See Baby Squirrels?

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    Tags: squirrel, baby animals, autumn, fall

    Created: 11/27/2012      Updated: 8/10/2016

    The simple answer is, baby squirrels don't leave the nest until they are fully furred and can survive on their own so, without seeing the mother right next to the babies, they all look about the same size. 

    Most babies leave the nest in April or May.  At this point the babies are fluffy and fat but the parents have exhausted their winter fat and are beginning to shed their winter fur, so look relatively small.  A second litter of babies may leave the nest around September.  At this point the parents have begun putting on fat and winter fur, so the apparent size difference can be greater.  Because of this, it may be easier to identify babies born late in the year. 

    Although baby squirrels have been recorded in almost every month of the year, these two litters, early spring and late summer, are the norm.  Typically the early spring babies have the highest survival rate, especially in areas where it snows, since a small squirrel has to expend more energy than a large one to stay warm and find food.

    I managed to take a few pictures of a baby and a young adult male that were foraging near each other in the same park.  Unfortunately, tree squirrels aren’t very social so I couldn’t get any useful pictures of them near each other, but they found my pen interesting so there is some scale.  The pen is about 16cm long.

    • Baby grey squirrelA baby grey squirrel.

    • Adult greay squirrel

      An adult grey squirrel from the same population as the baby in the previous photograph.

    • Adult grey squirrel

      Another view of the adult.  Note the more “mature” features. 

    Even with the specimens in-hand, assessing age can be somewhat qualitative but when the babies are very young, they are simply more cute than the rest of the population.

    If you're a squirrel watcher, like me, I hope you take the time to record your observations at projectsquirrel.org . Your data, combined with that of others around the country, helps us understand more about squirrels and about the nature in your neighborhood!

    Steve Sullivan, Senior Curator of Urban Ecology

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