Perhaps the most common native mammals in North America are mice.
The most widespread genus of native North American mice is Peromyscus, the “booted mice.”
They aren’t actually that closely related to the house mouse and other true rats and mice in the family Muridae.
They are actually in an entirely separate rodent family, Cricetidae. This family includes voles, lemmings, and hamsters in the Old World, and all the native rats and mice in the New World belong to this same family. Thus, the common native mice of North America are more closely related to hamsters than to house mice, which they superficially resemble.
It should be noted that within Peromyscus, the exact delineation of species isn’t exactly clear.
That’s because these mice are widely distributed across the continent, and because they are mice and do not travel vast distances from the place of their birth, they do have a lot of genetic diversity within the same species. Because of genetic drift, there are many regional varieties of these species.
However, the two most common species are phylogenetically distinct and are not capable of hybridization.
But they are almost identical and share almost the exact same ecological niche.
These two species are the deer mouse (P. maniculatus) and the white footed mouse (P. leucopus).
Deer mice are the more widespread of the two, ranging from northern Mexico to Alaska and Labrador. They are absent from the southeastern quarter of the United States.
White-footed mice are a bit less cosmopolitan in distribution. It ranges from southern Mexico to the US/Canadian border. A distjunct population can be found in the Canadian Maritimes, but its range in Canada is just north of the border in Southern Ontario and Quebec and parts of the prairie provinces that are adjacent to the US border. It is not found in northern Maine, and it is absent from the Northern Rockies, the Pacific Northwest, and virtually all of Canada.
There is no foolproof way of telling these animals apart. The best evidence I’ve seen suggested is that deer mice possess tails that have very clearly delineated white undersides that contrast with the dark top side.
But even that characteristic isn’t a foolproof way of identifying the species. Some white-footed mice have tails with clearly defined white undersides.
Some authorities will say that tail length is the best diagnostic feature. Deer mice usually have longer tails than white-footed mice, but that feature is so variable that one should be a bit cautious in using it.
Now, to make matters really complicated, white-footed mice have been known to hybridize with cotton mice (P. gossipynus). Enough of these hybrids are fertile because wild mice with genes belonging to one species have been found in individuals belonging to another.
Cotton mice are almost entirely restricted to the Southeastern United States. They do range up into Southern Illinois from adjacent Kentucky, but they range from southeastern Virginia to Florida and then west throughout the South. They are, however, absent from the Appalachians. There are a few places were one might find this species alongside deer and white-footed mice, but they mainly share territory with white-footed mice.
And no, cotton mice aren’t easy to tell apart from white-footed mice.
Because cotton mice and white-footed mice are at least partially interfertile, there is likely a species complex between the two that may make classifying them somewhat difficult. However, there is no evidence of a hybrid zone between the two species, and it appears they only hybridize when cotton mice populations are lower and the only available mates are white-footed mice.
Deer mice have something like a species complex operating within their populations. There can be significant chromosomal differences between subspecies, and it is possible that some of the subspecies of this mouse might be regarded as distinct species at some point.
The mice of this genus are quite notorious as a vectors for hantaviruses, but they have also been implicated as the major host species for Lyme disease.
And even though they have been readily bred in captivity as research animals, they have never been widely available on the pet market. The hantavirus thing sort of keeps them out of circulation, even though it’s virtually impossible for captive-bred mice to give their owners this disease.
Peromyscus is has more species in it than any other mammalian genus. There are currently 55 species in the genus, and deer mouse alone has 66 subspecies.
In North America, true mice are not native, but out of the vole-lemming-hamster family we have seen the evolution of what appear to be woodland mice.
These animals are commonplace, even banal.
But even in what appear to be such common animals is a really intriguing natural history.
I’d be remiss if I didn’t mention that when people keep pet Peromyscus, they often keep them with domestic house mice.
It doesn’t always work out, but one can create a multi-species cage for them if they do get along.
Here are two deer mice living with a group of domestic house mice:
This video should give you some idea about the relative size of the Peromyscus species when compared to the house mice we all know so well.