NATURAL HISTORY

By Kate Warren and Ian MacQuarrie

A nimals have a variety of gaits, with the pattern employed depending

upon habitat and circumstance. More-over, since much knowledge of the life and times of a species comes from inter-preting tracks, some attention to the dancing feet that make them is useful and often necessary. Basic biology, then, is not just counting teeth; it is looking at toes, and how these are picked up and put down.

For instance, there are six species of small rodents on Prince Edward Island that can generally be called "mice." These may be classified in many ways, such as by colour, size, similarity to Mickey. Their teeth provide useful infor-mation, particularly in terms of proper and improper mouse-handling tech-nique. They can also be divided into cursorial (running) and saltatory (jumping) groups. As most housekeep-ers can attest, the field mouse and house mouse are cursorial types. The jumpers are less familiar.

Small Differences

Prince Edward Island enjoys two species of jumping mouse. One of these is a grassland lover; the other prefers the

woods. They are very similar in size and colour: brown backs, yellow sides shad-ing to white underneath. The easiest way to tell them from the runners is by their tails, which are longer than their bodies. It is safe to assume that any mouse with such a long tail is a jumping mouse.

And how do you tell the jumping mice apart? Again, the tail distinguishes them: the woodland jumping mouse has a white-tipped tail, the meadow jumping mouse does not. Such minor differences may be lost on your cat, but they are mighty handy for naturalists.

These colour schemes are thus any-thing but mousy; they add to the charm of an encounter with a jumper. Perhaps you have seen one while walking along the edge of a hayfield or in the rough ground around a marsh. A tiny projectile rockets from under your feet and bounds off in a zigzag pattern. A jumping mouse in good condition can leap more than three metres, or perhaps 15 times its body length. It quickly goes to ground, relying on its camouflage for protection. If you leave it alone, it will go back to its summer schedule of eating (mostly seeds or fruit), sleeping (in a nest of grass under some cover), and reproducing (one to three litters averaging five young each). Both species spend the winter,

very sensibly, in hibernation. Aside from the tail tips, what are the

main differences between the two spe-cies? Evolution theory suggests that there must be some dissimilarities, or else one would compete strongly against, and perhaps eliminate, the other. There are, of course, differences in preferred habitat between woodland and meadow jumpers, but they also differ in social customs, behaviour. Both species are somewhat nomadic, but the grassland jumper is usually found alone, while the woodland type is much more sociable, even colonial, with its fellows. It is also more of a burrower, excavating tunnels a few centimetres below the surface. Thus, there are sufficient differences between the Island's jumping mice to

ensure that species-threatening compe-tition does not occur.

The Mouse that Soared

Jumping is a useful evasive action, and many animals that normally walk or run will jump for sheer survival when threat-ened. Adaptations for jumping may be more or less developed, varying from the strengthened hind limbs of rabbits and hares to a shifting of the centre of

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gravity toward the posterior, as in kanga-roos. In jumping mice, such physical adaptations include a shortened body, a greatly lengthened tail, and partial fus-ing of the bones of the foot to provide a better kick-off.

There are internal adaptations as well, relating to the elasticity of tendons and ligaments. The distance that an animal can jump may depend less upon size or strength than upon this elasticity. To understand this, think of an elastic band: when it is stretched, it acquires energy (it is this energy you feel when the band is released and hits your finger). The more the band is stretched, the more potential energy is stored in it. Of course, rubber bands (and ligaments) can be stretched too .4&tfM^4iife* far> but

in general the more elastic they are, the more energy can be stored in them.

The Achilles tendon of jumpers tends to be larger and more elastic than that of non-jumpers. When an animal lands af-ter the first jump, the tendon is stretched and energy is stored for use in the next take-off. This energy-return system al-lows for more and longer jumps, as the designers of sneakers seem to have suddenly realized. Jumping thus pro-vides good manoeuverability with a relatively low expenditure of energy — provided the habitat is suitable. Do not practise high jumps in low caves.

Most of the rodents that jump are desert dwellers, such as gerbils and kangaroo rats. Our local heroes are exceptional in dwelling around wood-lands and temperate grasslands. The meadow jumper ranges across Canada from British Columbia to Nova Scotia; the woodland type is more of an easterner, being found primarily from

Ontario eastwards. Neither species is listed as native to Newfoundland, al-though both could probably live there if introduced.

. . . and Counting

No one knows much about how many jumping mice there are on Prince Edward Island. In 1978, Bateman and Prescott found that the woodland jumping mouse was rare in the Prince Edward Island National Park; in 1954, another author had described it as "uncommon." On the other hand, Wilson found this species to be quite common in woodlands in the Montague area in 1988. Records from the University of Prince Edward Island's Biology Department suggest that the woodland jumper may be quite abun-dant locally in some habitat types, but that its numbers — even its presence — vary greatly from year to year.

Scientific Name

Size Range

Colouration

Habitat

The Family Dipodidae on Prince Edward Island

Meadow Jumping Mouse

Zapus hudsonius acadicus

Total length: 18-24 cm.

Weight: 12-25 g.

Woodland Jumping Mouse

| Napaeozapus insignis insignis

| Total length: 23-30 cm. * Tail length: 13-16, cm...

Weight: 16-27 g

Brown fur on back which fades to yellow on the sides and white on the belly. A road band of darker fur may be present on the back, running from nose to tail.

Along streams or rivers in grasslands or near marshes.

Reproduction \ 1-3 litters per year with an average of .^^JS^MM&P^ Utter. . _

Primarily seeds, but also fruit and some insects.

: Similar to that of the meadow jumping - mouse, however, the tail is tipped with - white.

Generally found close to streams or rivers in both coniferous and hardwood

I forests.

I 1-2 litters per year with an average of JAwwazMr

J, i

Fruit (especially apples, berries), seeds, roots, insects, fungi.

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A trick of the tail: the white-tail-tips identify these as woodland jumping mice.

In the same studies, the meadow jumping mouse was described as abundant in the Na-tional Park, but was not found in the Montague woodlands. The contrasting population densi-ties are probably due to the differences in habitat: the woodland jumping mouse likes forest; the meadow jumper prefers the open spaces. But some mammalogists believe that population differences through time may be explained by the sort of life history strategy that these mice have developed. They are geared to adult over-winter survival, rather than to rapid reproduction and high popula-tion densities.

In any case, there is no evidence that these winsome mice are endangered locally. Since they do not in any way menace human crops,* we can conclude that they are simply interest-ing, non-threatening, non-threatened species that share our Island way of life.

Sources

The general biology of the two jumpers is described in A. W. Banfield's classic The Mam-mals of Canada. Island information was ob-tained from Myrtle Bateman and Robert Prescott's Mammals of Prince Edward Island National Park, published by the Canadian Wildlife Service in 1984. In addition, the wood-land species turns up in Melvin Wilson's 1988 thesis (available in the Robertson Library) on the effects of forestry practices on small mam-mals in the Montague area.

The topic of locomotion in animals is dis-

Jumpingand Walking (1977) and R Alexander's Animal Mechanics (1968).

Finally, we wish to thank all of the jumping mice that we have encountered on many local field trips, in live traps, or through the good graces of an obliging cat. im

*Unlike their cousins, the meadow voles. See Ian MacQuarrie, "Plagues of Mice," Number 21 (Spring-Summer 1987).

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