_Behavior._--The saltatorial powers of _Z. hudsonius_ are well developed and often have been described in the literature. Stoner (1918:123) remarks that, "When disturbed _hudsonius_ moves away by a series of leaps ... the distance traversed in one of these leaps is from six to eight feet."; Cory (1912:249) observed these mice to make surprisingly long leaps, and, according to him, a distance of 10 feet is by no means unusual; Handley and Patton (1947:49) credit these animals with jumping eight to ten feet at a single bound; Hamilton (1935:190) remarked that he noted an average of not more than four to six feet per jump; Townsend (1935:91) observed one individual make jumps of about two feet; and Harper (1932:29) records a jumping mouse leaping for distances of two to three feet. Quimby (1951:72) notes that he had never seen one jump farther than three feet. He found that the greatest jumps occurred initially and normally covered a distance of two to three feet; subsequent leaps were shorter but more rapid. A jumping mouse in full retreat progressed by jumps of about one foot.
Statements concerning the gait of _Z. hudsonius_ are not in agreement but the consensus of opinion is that these animals when unfrightened progress by a series of hops of one to six inches, or, occasionally, with a slow creeping motion while the animal is on all fours. When frightened, however, their progress is by long bounds; the mice make a series of two or three such leaps to the nearest protective cover, and then sit motionless until pursued.
Concerning the use of the tail as a balancing organ, G. S. Miller (1899:330) describes the behavior of a jumping mouse from which the tail had been severed by the sickle of a mowing machine. "When I approached, it made violent efforts to escape, but the moment it was launched in the air, its body, deprived of its balancing power, turned end over end so that it was as likely as not to strike the ground facing the direction from which it had come."
Riparian animals such as _Z. hudsonius_ need enter the water to escape from enemies or perhaps in search of food. _Zapus hudsonius_ can and does swim. Hamilton (1935:190) found it to be a strong swimmer capable of remaining in the water for from four to five minutes. According to Hamilton (_loc. cit._), when the mouse is swimming the head is held high, the tail is arched near its middle, and only the hind limbs are employed in propulsion. According to Sheldon (1938:327), Philip Allan, in northern Minnesota, saw many _Z. hudsonius_ swimming three or four inches under the surface of the water. The mice swam upstream and only the hind legs were employed in the swimming movements. N. A. Preble (1944:200), at Archer"s Pond, 3 miles southeast of Center, Ossipee County, New Hampshire, observed a jumping mouse swimming rapidly under water toward another portion of the sh.o.r.e 30 or 40 feet away. The mouse, swimming less than a foot beneath the surface, was vigorously using both forefeet and hind feet, but the long tail trailing limply behind, contributed in no way to the animal"s movements. Quimby (1951:72) released five of the mice, one at a time, in the open water of a lake.
He followed alongside in a boat and observed that, "In all instances the animals proved to be excellent swimmers both on and underneath the surface. The methods of progression were similar to land movements; i.
e., the limbs were employed differently at various times depending upon the speed. When first placed in water they moved rapidly by lunges produced by sweeping strokes of the hind limbs employed simultaneously.
This movement was accomplished similarly to the long jumps made on land ... Following the first excited lunges, they settled down to a steadier and slower gait using all four limbs one at a time. The anterior part of the body was held high in the water ... When approached too closely, they attempted to escape by diving. The maximum distance noted was about four feet ... One was able to swim vigorously for approximately three minutes after which it tired greatly and was in danger of drowning."
As concerns digging ability, Goodwin (1935:148) reports that _Z.
hudsonius_ makes its own burrows; these are short and close to the surface in the summer but longer, deeper, and below the frost-line in winter. Two captives used their forefeet and nails in digging a tunnel in the foot of soil that Goodwin (_loc. cit._) had placed in their cage.
Quimby (1951:72) remarks that captives excavate soil by means of the front feet and throw the soil out behind; as the burrow deepened the hind feet were also utilized to throw the loose soil out of the burrow.
_Zapus hudsonius_ climbs; Sheldon (1934:293) observed captive animals to climb over small evergreen trees in their cages. They moved with surprising sureness and agility, chasing each other among the branches or sitting for several minutes at a time on one of the limbs. Hamilton (1935:190) found that the mice ran over limbs and brush which were placed in their outdoor enclosure.
Ordinarily _Z. hudsonius_ is nocturnal, appearing in the early dusk and remaining active until pre-dawn. Occasional individuals are abroad in daylight hours. Sheldon (1934:293) found in Nova Scotia that _Z.
hudsonius_ is most active from early dusk through the night, but that it may be abroad in daylight as well. Her statements are based on trapping results, field observations, and observations made on captive individuals. Quimby (1951:73) found that _Z. hudsonius_ in Michigan is mostly nocturnal; however, he saw mice on a few occasions in the daytime. Diurnal activity seems to be increased in cloudy or damp weather; Quimby (_loc. cit._) almost invariably trapped more of these mice on cloudy, damp days than on other days.
This jumping mouse usually is silent but does utter various sounds.
Sheldon (1934:295) records squeaking and clucking noises. Quimby (1951:73) records the clucking noise described by Sheldon (_loc. cit._) and mentions also the squeaking and suckling sounds produced by the small young. This mouse is most vociferous when young or when about to go into hibernation. Sheldon (1938:327) writes that _Z. hudsonius_ makes a drumming noise by vibrating the tail against dry leaves.
Many data are available concerning the hibernation of _Z. hudsonius_. In general it seems necessary for the mice to put on a certain amount of fat preparatory to hibernation. This fat is deposited in a thin layer over the inside of the skin, over the back, and in the body cavities.
The thickest deposits are in and about the inguinal region.
Quimby (1951:83) noted that gain in weight was accelerated in a brief period prior to entrance into hibernation. This relationship of rapid gain in weight to hibernation allows a person to estimate the date of hibernation. Cold weather seems to hasten hibernation, but less so than the correct physiologic condition which is foreshadowed by a rapid gain in weight. For example, Quimby"s (1951:84) data reveal that mice that were moved to a heated room gained weight and hibernated in a fashion similar to those in unheated surroundings. Hamilton (1935:193) states that, "It seems necessary for the mouse to lay on a certain amount of fat before it is capable of hibernation." Hamilton (_loc. cit._) reported that 18 specimens of _Z. hudsonius_ taken [presumably in an active state] near Ithaca, New York, on November 13, were without a trace of fat.
Data that are available concerning the hibernation sites of _Z.
hudsonius_ show that almost invariably these mice seek shelter in burrows beneath the surface of the ground and there construct nests of gra.s.s, leaves, or some other vegetation. Nicholson (1937:103) found a hibernating _Z. hudsonius_ on the George Reserve, Livingston County, Michigan, on October 20. The mouse was in a nest, composed of 10 to 12 damp elm leaves, in a sand bank two feet three inches vertically and three feet nine inches horizontally from the surface. On April 11, 1948, Schwartz (1951:228) found five nests (three with occupants) of _Z.
hudsonius_ at Jefferson City, Cole County, Missouri. All nests were one foot beneath the surface of a pile of coal-ash, which was about three and one-half feet high and five feet in diameter. The nests were spherical, approximately four inches in diameter and consisted of dried oak leaves and bits of dried gra.s.s. Grizzell (1949:74) found two hibernating jumping mice at the Patuxent Research Refuge, Laurel, Maryland, in January, 1948. The mice were in separate woodchuck dens; one mouse was 40 inches below the surface and the other was 26 inches below the surface. The mice were curled up in the center of ma.s.ses of dead leaves, and thus, were well insulated against the cold. On April 29, 1944, at Ithaca, New York, Eadie (1949:307) uncovered a hibernating jumping mouse. The nest, about the size of a baseball, was compactly made of fine gra.s.ses and was 10 inches below the surface of the ground in a mound of earth that was approximately six by four feet at the base and three feet high.
From the foregoing reports on hibernation sites it is evident that well drained areas are utilized. Sheldon (1934:300) remarks that the burrows used for hibernating are dug in a bank or some place from which the rain water and melted snow probably drains off.
Eadie (1949:307), Grizzell (1949:75), Sheldon (1934:299), Schwartz (1951:228), and Sheldon (1938:331) all agree that the hibernating mouse rolls up into a ball-like shape (resting on its head and pelvis) with the head between the hind legs, the nose against the lower belly, the forefeet curled on the chest, and the tail curled around the head and body.
A marked loss of weight occurs immediately after hibernation begins, and then reduction in weight is slow and regular. (See Hamilton, 1935:194 and Quimby, 1951:84.)
Sheldon (1934:297) cites a letter from Vernon Bailey in which he remarks on the necessity of abundant moisture and saturate air for hibernating jumping mice. Bailey writes "... they will awaken at times famished for water and will drink and drink before going back to sleep."
Hamilton (1935:195) thinks that in the Ithaca area of New York these mice probably leave their winter quarters in the second half of April and that in southern New York and Long Island they emerge considerably earlier. Quimby (1951:82) and Bernard Bailey (1929:163) report that males appear earlier in the spring than do the females. Quimby (_loc.
cit._), by recording the sequence and dates of phenological events and appearance of _Zapus_ in several years, was able to predict fairly accurately the time of emergence of _Zapus_ in a succeeding year. In Minnesota, jumping mice emerged late compared to other hibernating rodents.
_Enemies._--V. Bailey (1927:119) reports that A. K. Fisher found 50 skulls of _Zapus_ in barn owl pellets taken from the towers of the Smithsonian Inst.i.tution, Washington, D. C. Dearborn (1932:32) reported mink as having fed on jumping mice. Surface (1906:197) records taking a _Zapus_ from the stomach of a rattlesnake. Pearson and Pearson (1947:138) found remains of _Z. hudsonius_ in pellets of barn owls.
Quimby (1951:74) reports two cases of predation on _Z. hudsonius_; one was by a northern pike, _Esox lucius_ Linnaeus and the other was by a weasel, _Mustela_ sp. Vergeer (1948:91) collected a green frog, _Rana clamitans_ Latreille, which had eaten a jumping mouse.
Quimby (1951:74) frequently found the fleas, _Megabothris quirini_ Rothschild, and _Megabothris wagneri_ (Baker), and occasionally a larval tick, _Dermocenter variabilis_ (Say), on _Z. hudsonius_. Sheldon (1934:296) remarks that captive animals are burdened with numerous fleas. Hamilton (1935:191) removed a louse from a jumping mouse. One mouse had a hole in the throat and three others had holes in the inguinal region; presumably bot-flies had emerged from these holes. Test (1943:507) found a single _Cuterebra_ larva in the inguinal region of a _Z. hudsonius_, and Sheldon (1938:328) found _Z. hudsonius_ infested by larvae of _Cuterebra fontinella_ Clark. Here, as in other cases, these larvae were found immediately below the skin. Erickson (1938:252) examined 18 _Z. hudsonius_ obtained in Minnesota, and found that three were parasitized. He found a bot-fly larva, _Cuterebra_ sp., nematodes of the genera _Subulura_ and _Spirocerca_, and a fluke of the genus _Notocotylus_.
_Food._--Quimby (1951:85-86) studied the food preferences, by presenting to caged _Z. hudsonius_ the plants and invertebrate animals normally available to these mice in nature, and indicates that in general, the starchy fruits of the Gramineae and the less fleshy fruits of various groups of plants are more heavily utilized than other plant materials.
His observations indicate that these rodents are highly insectivorous and that they consume many insects under natural conditions. Goodwin (1935:148) reports that the stomach contents of several individuals obtained at South Woodstock, Connecticut, consisted exclusively of blackberries, and that others had subsisted princ.i.p.ally on cranberries.
Hamilton (1935:197) remarks that seeds are the favored food but that berries, nuts, fruits of various kinds, roots, and insects are also utilized. Stoner (1918:123) writes that the food in cultivated areas of Iowa is various grains as well as gra.s.s and weed seeds; in wooded places the mice feed on seeds and nuts of trees. Vernon Bailey (1927:118) states that the examination of a great many stomachs of these jumping mice [in North Dakota] revealed nothing "but the fine white pulp of carefully sh.e.l.led, well-masticated seeds. Generally these are from gra.s.ses, although grain and a variety of other plant seeds are eaten."
Schmidt (1931:116) examined the stomach contents of several _Z.
hudsonius_ taken in Clark County, Wisconsin, and in most stomachs found the remains of finely chewed roots; however, two from Hewett had eaten several geometrid caterpillars.
Lyon (1938:279), Stoner (1918:123), and J. W. Bailey (1946:263) present information which indicates that _Z. hudsonius_ stores food in its nests or burrows. Possibly these mice awaken at intervals from hibernation and eat.
"These rodents characteristically seize the material to be eaten with the front feet and devour it while reclining on their haunches. The following observation of a caged animal is typical of their feeding habits. The mouse selected a head of yellow foxtail, _Setaria glauca_ (Weig.) Stuntz, from several in the cage, separated it by gnawing through the supporting stem, seized it with the front feet, held it up to the mouth and began to gnaw at one end, stripping all parts from the rachis. The gra.s.s head was slowly rotated and shifted sideways until nothing remained but the rachis which was discarded. Actually the seeds were the only parts eaten ..." (Quimby, 1951:73). Sheldon (1934:294) remarks that _Z. hudsonius_ eats from a squatting position and holds the piece of food in the forepaws. The mouse seems to bite off a seed, and then, holding it in the forepaws, transfers it to the mouth.
According to Sheldon (_op. cit._:295) and Quimby (_loc. cit._), caged jumping mice drink water. When drinking, the mouths of the mice are in contact with the water, but neither observer determined whether the mice lapped or sucked the water. Sheldon (_loc. cit._) observed these mice pa.s.sing stems of long gra.s.s through their mouths as though to squeeze out moisture, and thought that the mice obtain most of their required moisture from green plants.
_Reproduction._--The breeding season begins shortly after the jumping mice emerge from hibernation in the spring, and reproduction continues until a few weeks before they hibernate in the autumn. The extent of the breeding period probably varies geographically and possibly seasonally.
For example, Quimby"s (_op. cit._:70) information suggests that the 1947 period of parturition occurred between June 15 and August 30 in the area of Centerville, Minnesota. In Michigan, Blair (1940:246) found a peak of breeding activity in spring and another in late summer with little activity in the intervening midsummer. Brimley (1923:263) records a female in North Carolina, with eight embryos on June 13, 1895, and another with seven embryos on September 17, 1891, indicating a strong possibility of two litters per year there. Vernon Bailey (1927:118) records young born in May or June in North Dakota and thinks that there is time for only one litter per year. Petrides (1948:76) captured a female on September 22, 1944, at Athens, Georgia, that gave birth to six young on September 29. This late parturition date indicates a longer breeding season in the southeastern part of the range of _Z. hudsonius_.
The gestation period of nonlactating, caged _Z. hudsonius_, Quimby (1951:63) thinks, "is approximately 18 days ... [but] gestation is prolonged in lactating females."
Data from museum labels indicate that embryos in 62 pregnant females averaged 5.4 (2-8) per female. Quimby (1951:67) found the average number of embryos per female for 14 females taken in Minnesota, to be 5.3 and that litters of young found in nests averaged 5.8. Sheldon (1938:330) reports two litters of seven young each and one of four young for _Z.
hudsonius_ in Vermont. Petrides (1948:76) records a litter of six young for _Z. hudsonius_ in Georgia. Brimley (1923:263) records one lot of seven and one lot of eight embryos for _Z. hudsonius_ in North Carolina. Vernon Bailey (1923:120) reports six embryos for a female of _Z. hudsonius_ taken in Washington, D. C. Ivor (1934:8) obtained a litter of five young _Z. hudsonius_ from Erindale, Peel County, Ontario.
Hamilton (1935:195) records litters of two, four, and five young and embryo counts of four, two, four, and four for _Z. hudsonius_ in New York.
There seems to be two litters per year. According to Quimby (1951:69), "most adult females breed soon after emergence from hibernation and produce the first litters within a month. The remaining females do not breed immediately but produce the first litter," he says, "in the second month after emergence." Both early-breeding females and late-breeding females produce at least 2 litters per year. Those that breed early may have 3 litters.
The appearance and development of growing young of _Z. hudsonius_ in successive weeks is described by Quimby (1951:65). Newborn young are pink and hairless except for microscopic vibrissae. The eyes and external auditory meatus are closed, and the pinnae are folded. The toes are fleshy and clawless; the tail is short in relation to the length of the body. The average weight was .78 grams. The average measurements of three from different litters are: total length, 34 mm; tail, 9.2 mm; hind foot, 4.7 mm. The young are helpless but capable of emitting a high pitched squeaking sound which is audible for several feet.
In the first week of growth the vibrissae become visible to the naked eye, the body changes to flesh color, the dorsal parts become dark gray, the pinna unfolds and is black tipped, and the claws appear. The young now are able to crawl and make a suckling noise, but they are not yet able to support themselves on their legs.
In the second week of development, tawny yellow hair appears on the back and spreads onto the sides. Spa.r.s.e hair of a lighter color appears on the belly, backs of the feet, and outer surfaces of the legs. Vibrissae are now prominent. The eyes are still closed, but a crack down the center of each is visible by the 13th day. Claws have grown, the longest measuring 1.5 mm. The incisors erupt on approximately the 13th day, those in the lower jaw appearing slightly before those in the upper jaw, and all are white. Activity is increased; nevertheless the young still crawl, make suckling notes, and squeak.
In the third week of development the mice are covered with hair; darker hair appears dorsally; and vibrissae continue rapid growth. The external auditory meatus begins to open on about the 19th day and young react to sound on the 20th. The incisors now are 1 mm long and the claws 1.5 mm long. Young are able to support themselves on their legs, walk, and make one inch hops.
In the fourth week the juvenal pelage is replaced by adult pelage. The eyes open between the 22nd and 25th days. The color of the incisors changes from white to yellowish-orange as in the adults. P^4, M^1, M^2, m1 and m2 have emerged from the maxillary and dentary bones; M^3 and m3 have not yet erupted. A mouse 33 days old had all teeth well developed.
By the end of the 4th week the young, except for size, are adultlike and capable of independent existence.
The greatest increase in dimensions of the body is in the first four weeks. A slowing down of growth is simultaneous with weaning.
Other workers, Sheldon (1938:330), Petrides (1948:76), and Ivor (1934:8) also describe the appearance of the young.
Summer nesting sites are usually on the surface of the ground. Jumping mice characteristically construct a globular nest of gra.s.s but will utilize other vegetation if gra.s.ses are not available. Nests are usually concealed under rocks, logs, bushes, or gra.s.s and can be entered by a hole at one side.
Sheldon (1938:328) described a nest of _Z. hudsonius_ found on the ground near the edge of a small hay field. The nest was globular, not more than four inches in outside diameter and two inches in inside diameter; it was closely woven of fine, dry gra.s.s and bits of moss.
Another nest found in the same field measured 11.5 inches in circ.u.mference at the base and six inches in circ.u.mference over the top.
The inside width and length each was three inches, and the inside height was 3.5 inches. Vernon Bailey (1927:118) remarks that summer nests are placed on the surface of the ground well concealed under gra.s.s or other vegetation. He describes the nest as "neat little b.a.l.l.s of fine gra.s.s with a tiny opening at one side and a soft lining in the central chamber." Cory (1912:249) reports that summer nests are concealed behind rocks or under bushes and thick gra.s.s. The nests are round and four or five inches in diameter with an entrance hole at one side. Goodwin (1935:148) examined a nest made entirely of straight, narrow leaves of gra.s.s. Ivor (1934:8) found one made of finely shredded jute sacking.
Quimby (1951:80) describes several nests: one in the center of a rotten willow log was lined with small pieces of pulpy wood; another was in the rotted wood and debris, at ground level, inside a large, red oak (this globular nest composed of gra.s.ses, plant fibers, and rootlets measured six inches in diameter). Another nest was composed of a pile of wood pulp, leaves of oaks, and gra.s.ses; this nest was in a hollow root detached from a willow tree.
The mean home range of males, of _Z. hudsonius_ in Minnesota, according to Quimby (1951:86), was 2.70 plus or minus .50 acres; this was significantly larger than the mean home range of females, 1.57 plus or minus .27 acres. According to Quimby (_loc. cit._), the size and shape of the home range is influenced by the general features of the terrain, density and type of cover, and land use in the immediate area. Quimby (1951:94) remarked that the home range of the jumping mouse is relatively unstable and Blair (1940:247) stated that the home ranges of both s.e.xes generally overlapped the ranges of other members of the same species and s.e.x. The average size of the home range for _Z. hudsonius_ in Michigan was .89 plus or minus .11 acres for males and .92 plus or minus .11 acres for females.
=Zapus hudsonius acadicus= (Dawson)
_Meriones acadicus_ Dawson, Edinburgh New Philos. Jour., new ser., 3:2, 1856.