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 Age
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.
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.