Month: August 2016

Why Do Squirrels Have Fluffy Tails?

One of a squirrel’s most distinctive features is her big, fluffy tail. In fact, about half a squirrel’s length is taken up by her tail.1 Other rodents like mice and rats have tails of similar length but without all the fluff. So does this big tail give squirrels any particular advantage?

It turns out that squirrels use their tails for all sorts of things. Fluffy tails help squirrels communicate with each other, perform arboreal acrobatics, and survive extreme temperatures.

Squirrel-to-Squirrel Communication

Squirrels use their prominent tails to communicate with each other in a form of sign language. There are two main types of tail signals. The first is a small up-and-down undulation, and the second is a larger whipping motion.2 This whipping motion is a squirrel’s way of giving an alarm that a predator is near.3 It’s especially associated with indicating to other squirrels that a land-based predator, as opposed to a hawk or other aerial predator, is approaching.4

A High-Wire Balancing Act

Squirrels are often seen running along precariously thin branches and power lines. So how do they keep their balance? A long tail can help an animal run confidently through the treetops by serving as a counterbalance to the animal’s body weight.5 Think of the way a tightrope walker uses a long pole to stay upright on a wire. If a squirrel running along a narrow branch starts slipping off one side, she can move her tail in the opposite direction to balance herself out.

Squirrel running along a power line.
Squirrel running along a power line.

Of course, sometimes even squirrels take a fall. When that happens, their tails once again come in handy. A squirrel’s tail can act as a parachute to slow her down during a fall and then cushion her when she hits the ground.6

Staying Warm and Keeping Cool

Squirrels are active year round, so they need a way to stay warm in the winter and cool in the summer. Apparently, a big, furry tail is the perfect solution. One of the most common postures a squirrel will adopt is to sit with her tail curled over her head like a fuzzy umbrella. Not only does this tail umbrella protect a squirrel from the rain, but it helps her stay cool by shading her from the sun.6 Unsurprisingly, a squirrel’s furry tail also keeps her – and her babies – warm and cozy in colder weather.6

Related Posts

References

1 Webster, D., Parnell, J., & Biggs, W. (1985). Mammals of the Carolinas, Virginia, and Maryland. Chapel Hill and London: The University of North Carolina Press.

2 McRae, T. (2012). Predator-specificity of multimodal alarm signals in the eastern gray squirrel (Sciurus carolinensis). Open Access Dissertations, Paper 736. Retrieved from http://scholarlyrepository.miami.edu/cgi/viewcontent.cgi?article=1748&context=oa_dissertations

3 Jayne, K., Lea, S., & Leaver, L. (2015). Behavioral responses of Eastern grey squirrels, Sciurus carolinensis, to cues of risk while foraging. Behavioural Processes, 116: 53-61.

4 McRae, T. & Green, S. (2014). Joint tail and vocal alarm signals of gray squirrels (Sciurus carolinensis). Behavior, 151(10), 1433-1452.

5 Young, J., Russo, G., Fellmann, C., Thatikunta, M., & Chadwell, B. (2015). Tail function during arboreal quadrupedalism in squirrel monkeys (Saimiri boliviensis) and tamarins (Saguinus oedipus). Journal of Experimental Zoology, 9999, 1-11. Retrieved from http://www.academia.edu/14055165/Tail_Function_During_Arboreal_Quadrupedalism_in_Squirrel_Monkeys_Saimiri_boliviensis_and_Tamarins_Saguinus_oedipus_

6 Haupt, L. (2013). The urban bestiary: encountering the everyday wild. New York, NY: Little, Brown and Company.

How to Release a Squirrel into the Wild

Whether you’ve raised a baby squirrel to adulthood or nursed a sick squirrel back to health, at some point you’ll need to return her to the wild where she belongs. However, this isn’t as easy as just dumping your furry friend into the nearest backyard. A successful release depends on both preparing your squirrel for independence and finding a good place for her to live.

When Should a Squirrel Be Released?

Basically, squirrels can be released when they’re able to find food and shelter while avoiding predators. Use the following physical and behavioral signs to determine whether your squirrel is ready to survive on her own.

Physical Signs1

  • Is at least 12 weeks old
  • Weighs 350 grams or more
  • Appears overall healthy and in good condition

Behavioral Signs1

  • Will eat natural foods
  • Is able to forage successfully
  • Can open hard shells, like those of walnuts
  • Runs away from humans and pets

Choosing a Good Release Site

When you’re confident that your squirrel is able to be independent, it’s time to scope out a new home for her. Some characteristics of a good release site include a limited number of predators in the area, easy access to safety and shelter, and an abundant source of food. The ideal habitat for gray squirrels contains plenty of oak, hickory, and beech trees.2 These types of trees both provide shelter and produce some of the best nuts for squirrels. Since established squirrels can respond aggressively to newcomers,3 try to find a release spot that has fewer squirrels already in residence.

Preparing Your Squirrel for a Successful Release

To give your squirrel the best chance of thriving in her new home, it’s important to acclimate her to the site prior to release.1 This requires allowing her to spend some time in it in a controlled manner. Simply relocate your squirrel to a large cage on-site for a few days or, if you’ve raised the squirrel and she’s used to being handled, you can even let her roam freely for a few hours every day and she’ll still come back to you. Doing so will both familiarize your squirrel with the area and allow her to accustom herself to out-of-door temperatures and weather conditions.

On the Day of the Release

Squirrels are active during the day and sleep at night,4 so a good time for the actual release is in the morning. Make sure your squirrel is fed and fully hydrated before letting her go. She should be allowed to enter the release site of her own accord. For example, if you’ve housed her in a cage, just leave the door open and let her exit when she’s ready.

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References

1 Cherney, L. & Nieves, M. (1991). How to care for orphaned wild mammals. Iowa State University Veterinarian, 53(2), 94-99. Retrieved from http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=3394&context=iowastate_veterinarian

2 Webster, D., Parnell, J., & Biggs, W. (1985). Mammals of the Carolinas, Virginia, and Maryland. Chapel Hill and London: The University of North Carolina Press.

3 Thompson, D. (1978). The social system of the grey squirrel. Behavior, 64(3), 305-328.

4 Reid, F. (2006). A field guide to mammals of North America (4th ed.). New York, NY: Houghton Mifflin Company.

Why Are Some Gray Squirrels Black?

Black squirrel picture
This black squirrel is a gray squirrel!

If you have squirrels with gray-colored fur in your neighborhood, you’ve probably correctly identified them as eastern gray squirrels. Eastern gray squirrels are the type of squirrel most commonly found in urban and suburban environments.1 Less widely known is the fact that black “suburban” squirrels are also eastern gray squirrels. So why are these supposedly “gray” squirrels black?

The hair of all mammals, including squirrels and humans, contains a pigment called melanin. Mammals produce two different types of melanin, a light-colored version and a dark-colored version.2 The amount of these light and dark pigments present in a squirrel’s fur is what gives the squirrel its distinctive color.

In normal gray squirrels, both light- and dark-colored melanin is deposited in the hair in layers.2 The result is an overall gray appearance. However, some gray squirrels have a mutation that makes their fur black.2 The hair of these squirrels contains much higher quantities of the darker shade of melanin.

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References

1 Haupt, L. (2013). The urban bestiary: encountering the everyday wild. New York, NY: Little, Brown and Company.

2 McRobie, H., Thomas, A., & Kelly, J. (2009). The genetic basis of melanism in the gray squirrel (Sciurus carolinensis). Journal of Heredity. Retrieved from http://jhered.oxfordjournals.org/content/early/2009/07/30/jhered.esp059.full

How to Feed Baby Squirrels

For the first 7 weeks of their lives, baby squirrels survive solely on milk from their mothers.1 Puppy milk formulas like Esbilac powder make a great replacement for squirrel milk. You can also use standard kitchen ingredients to formulate your own squirrel milk using this Easy Squirrel Milk Recipe.

How to Nurse Baby Squirrels

Feeding milk to baby squirrels requires “specialized” equipment. A syringe or dropper works nicely. If you choose to use a syringe, make sure it’s made of glass. A baby squirrel will gnaw on a plastic syringe, wearing it down and potentially ingesting plastic. Another consideration when choosing your equipment is the size of the opening. To prevent your squirrel from feeding too quickly and choking or getting fluid in his airways, choose a syringe or dropper with a small opening.2

Baby squirrel drinking milk from a syringe.
Baby squirrel drinking milk from a syringe.

What About Solid Food?

Baby squirrels can start to eat solid food when their eyes open at around 5 weeks of age.2 Their incisor teeth should be grown in by then, so it’s ok to give them harder foods as long as those foods aren’t surrounded by a shell. In fact, the ability to crack a walnut is a sign that a young squirrel is ready to be released.2

How to Wean Baby Squirrels

The weaning process begins when a young squirrel is 8 weeks old and will last for 2 to 4 weeks.1,2,3 Therefore, a squirrel should be eating only solid foods by the time he is 10 – 12 weeks old. To wean your squirrel, you’ll need to introduce solid food into his diet while reducing his milk intake. There are two obvious ways to do this.

The most straightforward method is to replace a portion of the milk with solid food. Then, increase the proportion of food to milk every week. A feeding schedule based on this method might look like this:

Age                  Food
1 – 7 weeks        only milk
8 weeks              replace 1/4 of milk with solid food
9 weeks              replace 1/2 of milk with solid food
10 weeks            replace 3/4 of milk with solid food
11 weeks             only solid food

Another method of weaning squirrels is to start diluting the milk with water at 8 weeks of age and adding solid food to the squirrel’s diet at the same time. Since the composition of a mother squirrel’s milk changes over the course of the nursing period,1 this method might be preferable. Here’s an example of a feeding schedule using the dilution method:

Age                  Food
1 – 7 weeks        only milk
8 weeks             dilute milk until 1/4 of it is water; add solid food
9 weeks             dilute milk until 1/3 of it is water; add solid food
10 weeks           dilute milk until 1/2 of it is water; add solid food
11 weeks            only solid food

Related Posts

References

1 Nixon, C., & Harper, W. (1972). Composition of gray squirrel milk. The Ohio Journal of Science, 72(1), 3-6. Retrieved from https://kb.osu.edu/dspace/bitstream/handle/1811/5665/V72N01_003.pdf?sequence=1

2 Cherney, L. & Nieves, M. (1991). How to care for orphaned wild mammals. Iowa State University Veterinarian, 53(2), 94-99. Retrieved from http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=3394&context=iowastate_veterinarian

3 Webster, D., Parnell, J., & Biggs, W. (1985). Mammals of the Carolinas, Virginia, and Maryland. Chapel Hill and London: The University of North Carolina Press.

How to Figure Out the Age of a Baby Squirrel

If you’ve found a baby squirrel, you’re probably wondering how old it is. Figuring out the age of a baby squirrel is a little tricky but not impossible. It’s especially important to have this information if you plan on raising the squirrel and need to decide what to feed her, when to release her, etc.

Most methods for determining the age of squirrels have been developed by scientists for research purposes. For example, X-rays can be used to measure bone fusion and growth, and the weight of a squirrel’s eye lens gives a reliable indication of age as well.1 Obviously, these methods don’t help us because a.) they require expensive, specialized equipment and b.) we don’t want to sacrifice and dissect our baby squirrel.

Fortunately, there are alternative ways to gauge the age of squirrels. These methods rely on observations of both the time of year and the baby squirrel’s physical development. Even though there’s no way to know precisely how old a squirrel is, you should be able to make a pretty good approximation using the following information.

Using the Time of Year to Age Baby Squirrels

The month in which you find a baby squirrel can give you a rough idea of its age. Since we know most squirrels are born in either March or July, simply count backwards on a calendar to estimate her age in months. Squirrels become self-sufficient at around 10 – 12 weeks of age,2,3 so you shouldn’t find any “baby” squirrels that are more than 3 months old.

Using the Rate of Physical Development to Age Baby Squirrels4

Like people, squirrels are born without any hair or teeth. Their eyes and ears are also closed at birth. Noting the development of these characteristics can give you a fairly accurate idea of a squirrel’s age in weeks. This method is only useful for very young squirrels because by the time they’re about 6 weeks old, all these traits will be present.

Fur – Hair first appears on the backs of squirrels at around 2 weeks of age and will grow to be 1 mm long by the third week. When the white hair on the tail is 2 mm long, the squirrel is about 4 weeks old. Fur will cover the underside of the tail (facing the belly) when the squirrel is 6 weeks of age.

Teeth – The appearance of a squirrel’s incisors, the sharp, prominent teeth in the front of a squirrel’s mouth, can also be used to help age a squirrel. The lower incisors come in first at about 3 weeks of age. Typically, the upper incisors don’t come in until the squirrel is about 4 1/2 weeks old.

Eyes – The age at which baby squirrels open their eyes can vary by several weeks. Most squirrels will have open eyes, either clear or cloudy, by the time they’re 5 weeks old. However, baby squirrels have been known to start opening their eyes by as early as 3 1/2 weeks and as late as 6 weeks.

Ears – Baby squirrel ears usually open when the squirrel is 3 – 4 weeks old.

Every child develops at a different rate, and as you can see, juvenile squirrels are no different. Instead of relying on a single attribute to determine age, it’s better to take all of the characteristics listed above into account along with the time of year. You can also use this handy tool to estimate the age of your squirrel.

Example of How to Estimate a Baby Squirrel’s AgeBaby squirrel age example

As you can see in the example above, this young squirrel’s eyes and ears are open, so he’s at least 3 1/2 weeks old. However, we know he’s younger than 6 weeks of age because the fur on the underside of his tail hasn’t quite filled in yet. The white fur on the tail is definitely longer than the 2 mm usually seen at 4 weeks. Therefore, this squirrel is probably about 5 weeks old.

Related Posts

References

1 Dubock, A. (1979). Methods of age determination in Grey squirrels (Sciurus carolinensis) in Britain. Journal of Zoology, 188(1), 27 – 40. Retrieved from https://www.researchgate.net/publication/230109361_Methods_of_ageing_Grey_squirrels_Sciurus_carolinensis_in_Britain

2 Reid, F. (2006). A field guide to mammals of North America (4th ed.). New York, NY: Houghton Mifflin Company.

3 Webster, D., Parnell, J., & Biggs, W. (1985). Mammals of the Carolinas, Virginia, and Maryland. Chapel Hill and London: The University of North Carolina Press.

4 Uhlig, H. (1955). The determination of age of nestling and sub-adult gray squirrels in West Virginia. The Journal of Wildlife Management, 19(4), 479-483.