Age groups | 4 | 5 | 6
---------------+------------+------------+------------
Number | | |
examined | 14 | 3 | 3
| | |
Occipitonasal | 22.7 | 22.9 | 23.0
length | 21.8 23.4 | 22.7 23.3 | 22.4 23.7
| | |
Mastoid | 10.12 | 10.3 | 10.36
breadth | 9.6 10.7 | 10.0 10.8 | 10.1 10.8
| | |
Length of | 9.25 | 9.5 | 9.35
zygomatic arch | 9.2 9.4 | 9.5 9.5 | 9.1 9.6
| | |
Breadth of | 3.44 | 3.66 | 3.45
palate at P4 | 3.1 3.7 | 3.6 3.7 | 3.4 3.5
| | |
Breadth of | 2.74 | 3.11 | 2.77
palate at M3 | 2.5 3.0 | 3.0 3.2 | 2.6 2.9
| | |
Palatal | 9.59 | 9.73 | 9.8
length | 9.0 10.0 | 9.5 9.9 | 9.6 10.1
| | |
Distance from | | |
incisors to | 9.68 | 9.73 | 9.80
postpalatal | 9.2 10.0 | 9.5 9.9 | 9.6 10.1
notch | | |
| | |
Interorbital | 4.2 | 4.23 | 4.2
breadth | 4.0 4.4 | 4.1 4.4 | 4.2 4.2
| | |
Average length | | |
of upper | 3.22 | 3.2 | 3.16
molar series | 2.9 3.5 | 3.2 3.2 | 3.1 3.2
| | |
Breadth of | 9.68 | 9.83 | 9.63
braincase | 9.3 10.0 | 9.5 10.2 | 9.3 9.9
| | |
Zygomatic | 10.80 | 11.0 | 11.25
breadth | 10.7 11.2 | 10.5 11.5 | 11.2 11.3
| | |
Condylobasal | 19.33 | 19.6 | 19.9
length | 18.5 19.9 | 19.4 19.8 | 19.5 20.3
---------------+------------+------------+------------
Individual Variation
Measurements of external parts in _Zapus_ are more variable than are
measurements of most parts of the skull. As Hoffmeister (1951:16) points
out for _Peromyscus truei_, this variation in external features results
in part from "the difficulties in accurately measuring soft parts of the
anatomy" and also from inconsistencies on the part of collectors in
making these measurements.
A comparison of coefficients of variation (see table 3) for cranial
measurements between populations of like age and sex for the species _Z.
hudsonius_, _Z. princeps_, and _Z. trinotatus_ shows that variation of
approximately the same degree is recorded in corresponding elements in
all species; that is to say, structures which are most variable
individually in _Z. princeps_ are also most variable in _Z. trinotatus_
and _Z. hudsonius_.
Individual variation in the occlusal pattern of the molariform teeth is
slight. In several specimens, however, the re-entrant fold is absent
from the lingual surface of M1. Teeth in addition to the normal number
were recorded for five specimens. In all instances they are in the upper
dentition and usually at the posterior end of the maxillary tooth-row.
In each of four specimens (KU No. 34852, KU No. 32852, MVZ No. 52105,
all _Z. princeps_, and USBS No. 22921, _Z. hudsonius_), there is only a
single additional tooth. One individual (USBS No. 264388, _Z. princeps_)
possessed two extra molars, one in each maxillary tooth-row. The extra
teeth vary in size from those which are only slightly smaller than the
adjacent normal molars to those which are simple, peglike structures. In
four of the five animals the extra teeth are posterior to the normal M3;
in the fifth (MVZ No. 52105) the added tooth is anteriormedial to M3.
TABLE 3.--Coefficients of Variation for Dimensions of Corresponding
Parts of the Skull of Three Species of Zapus. The Specimens of
Zapus hudsonius are from Menominee and Keweenaw counties, Michigan,
the Zapus princeps are from the Vicinity of Encampment, Wyoming,
and the Zapus trinotatus from Huntingdon, British Columbia.
==============================+=============+============+==============
| _Z. h._ | _Z. p._ | _Z. t._
Species | _hudsonius_ | _princeps_ | _trinotatus_
------------------------------+-------------+------------+--------------
No. examined | 52 | 46 | 19
| | |
Mastoid width | 2.85 | 1.98 | 2.21
| | |
Occipitonasal length | 2.64 | 1.37 | 1.20
| | |
Incisors to postpalatal notch | 3.02 | 2.56 | 2.56
| | |
Interorbital constriction | 2.75 | 3.66 | 3.22
| | |
Zygomatic breadth | 2.74 | 2.54 | 1.94
| | |
Maxillary tooth-row | 4.50 | 4.44 | 3.82
------------------------------+-------------+------------+--------------
The size and shape of certain cranial elements vary individually even
between right and left sides of the same animal. The paired parietal
bones in some animals are nearly square and identical. In other animals
these bones are approximately equal and straight on three sides with the
fourth side forming an anterolateral projection; this projection may be
slightly or greatly produced, and opposite elements in a single
individual differ in this respect.
The interparietal also is variable; the lateral arms may be blunted and
not included in the fusion of the squamosal, parietal, and occipital
elements, or the interparietals may be elongated and fused with these
elements. Posterior and anterior borders of the interparietal may be
straight, produced anteriorly, produced posteriorly, or produced
anteriorly and posteriorly.
There is frequently variation in the degree of taper of the nasals. They
may be parallel sided, narrowed distally, or narrowed proximally. There
is some variation in the degree of inflation, in the size, and in the
shape of the frontal bones. The anterior surface of the postpalatal
notch varies individually and may be truncate, anteriorly convex, or
anteriorly concave.
Individual variation in the color of the pelage of animals that are in
the same stage of molt or non-molt is by my observation slight. The
presence of oil in the hair results in a false impression of sleekness
and seemingly darker pigmentation. Abnormal white-spotting dorsally
occurs as does yellow and melanistic coat color. These mutations are
considered in the discussion concerning pelage.
Secondary Sexual Variation
In specimens of the two sexes from similar age groups of _hudsonius_
from Michigan, the mean values for each measurement for the two sexes
differ only slightly or are essentially the same (see table 4). In no
species has secondary sexual variation been found to be greater than
individual variation.
TABLE 4.--Mean Measurements for Adult Male and Female Z. hudsonius
of Age Group 2 and Per Cent Difference of Females to Males
(Specimens from Michigan).
==============================+=========+=========+=====================
| | | Per cent difference,
Sex | Male | Female | females to males
------------------------------+---------+---------+---------------------
No. examined | 18 | 15 |
| | |
Total length | 202.85 | 202.88 | 0.02% larger
| | |
Hind foot | 122.85 | 122.10 | 0.60% smaller
| | |
Mastoid width | 10.10 | 10.28 | 1.50% larger
| | |
Occipitonasal length | 22.15 | 22.03 | 0.55% smaller
| | |
Incisors to postpalatal notch | 9.39 | 9.33 | 0.64% smaller
| | |
Zygomatic breadth | 10.47 | 10.57 | 0.95% larger
| | |
Maxillary tooth-row length | 3.52 | 3.60 | 0.23% larger
------------------------------+---------+---------+---------------------
CHECK-LIST OF THE SPECIES AND SUBSPECIES OF THE GENUS _ZAPUS_
PAGE
_Zapus trinotatus_ 385
_Zapus trinotatus eureka_ A. B. Howell 389
_Zapus trinotatus montanus_ Merriam 390
_Zapus trinotatus orarius_ Preble 391
_Zapus trinotatus trinotatus_ Rhoads 392
_Zapus princeps_ 394
_Zapus princeps cinereus_ Hall 399
_Zapus princeps curtatus_ Hall 400
_Zapus princeps idahoensis_ Davis 401
_Zapus princeps kootenayensis_ Anderson 404
_Zapus princeps luteus_ Miller 406
_Zapus princeps minor_ Preble 407
_Zapus princeps oregonus_ Preble 409
_Zapus princeps pacificus_ Merriam 412
_Zapus princeps princeps_ Allen 414
_Zapus princeps saltator_ Allen 416
_Zapus princeps utahensis_ Hall 418
_Zapus hudsonius_ 420
_Zapus hudsonius acadicus_ (Dawson) 432
_Zapus hudsonius alascensis_ Merriam 435
_Zapus hudsonius americanus_ (Barton) 436
_Zapus hudsonius campestris_ Preble 441
_Zapus hudsonius canadensis_ (Davies) 442
_Zapus hudsonius hudsonius_ (Zimmerman) 443
_Zapus hudsonius intermedius_ Krutzsch 447
_Zapus hudsonius ladas_ Bangs 449
_Zapus hudsonius pallidus_ Cockrum and Baker 450
_Zapus hudsonius preblei_ Krutzsch 452
_Zapus hudsonius tenellus_ Merriam 453
Genus =Zapus= Coues
_Genotype._--_Dipus hudsonius_ Zimmerman.
EXTERNAL CHARACTERS.--Muriform in general appearance; forelimbs small,
short; hind limbs greatly developed; hind feet long and narrow; tail
tapering, attenuate, subcylindrical; head long and mouse-shaped; eyes
small and situated midway between nose and ear; external ear somewhat
longer than surrounding hair and provided with antitragal flap which can
cover external auditory meatus, and in company with tragus completely
close opening; upper lip without median groove; internal cheek-pouches
well developed and opening at corners of mouth; mystacial vibrissae
conspicuous; supercilliary vibrissae few; genal tuft absent; teats
normally eight and arranged in pairs (one pectoral, two abdominal, and
one inguinal); anterior and posterior pairs frequently undeveloped;
general pelage coarse; color of pelage varies somewhat in different
species but always follows single basic pattern of broad dorsal band of
some shade of brown or brownish-yellow darkened with brownish-black,
sides of a lighter tone and slightly streaked with brownish-black,
underparts snow-white, sometimes suffused with color of the sides and
usually separated from color of sides by sharp line of clear
brownish-yellow; backs of forefeet and hind feet grayish-white; tail
distinctly bicolor, dark brown above and yellowish-white below; ears
dark and narrowly edged with light color.
[Illustration: FIG. 44. Map showing distribution of the genus
_Zapus_.]
CRANIAL CHARACTERS.--Skull short in relation to width, deep relative to
other dimensions, somewhat convex; delicate, papery, without strong
angularity; braincase relatively unexpanded; antorbital foramen
obliquely oval and transmits masseter muscle of great size; foramen in
inferior ramus of zygomatic process of maxillary for passage of superior
maxillary branch of trigeminal nerve small; zygomata not wide-spreading;
underside of zygoma nearly horizontal, upper edge anteriorly rises
prominently owing to extension of jugal upward along maxillary; jugal
and lachrymal in contact; one ramus of zygomatic process of maxilla
arises directly above other; rostrum thick basally and relatively
attenuate distally; ends of nasals project noticeably beyond incisors;
premaxillaries develop strong alveolar plate separating superior
incisors for half their length; palatal bones shortened posteriorly,
free edge often concave; incisive foramina long, broad, and separated by
bulbose (except at posterior end) bony septum; mastoid bullae absent;
auditory bullae short and transversely placed; postorbital process never
present; parietals nearly square, sometimes emarginate in front; angle
of mandible flattened and bent inward; coronoid process weak, acute, and
slopes strongly upward.
DENTAL CHARACTERS.--Dental formula
I 1, C O, P 1, M 3
-- -- -- -- -- -- -- -- = 18;
i 1 c o p o m 3
upper incisors short, compressed, curved backward, and strongly grooved;
lower incisors slender, curved backward, and ungrooved; both upper and
lower incisors deep orange or yellow; four upper cheek-teeth present;
premolar small, single rooted and, sometimes, non-functional; upper
molars tri-rooted, sub-hypsodont, and with occlusal surface
non-cuspidate (flat); enamel pattern, much complicated, consisting of
one main re-entrant fold lingually and four re-entrant folds labially;
three lower molars, bi-rooted, sub-hypsodont, flat crowned, with two
outer and four inner re-entrant folds.
POSTCRANIAL CHARACTERS.--Neck short and weak; atlas large; axis separate
from atlas; remaining (5) cervical vertebrae also free; thoracic (12)
and lumbar (7) vertebrae strongly built; posterior lumbars with enlarged
neural and anteriorly directed transverse processes; sacral vertebrae
(7) as in murids; caudal vertebrae variable in number (average 36);
clavicle long, slender, uniformly curved, convex outwardly; scapula with
supraspinous and infraspinous fossae of equal size; forelimbs short,
approximately half as long as hind limbs; hind limbs elongate, slender;
femur with third trochanter; tibia and fibula fused slightly distal to
middle of former; five elongate, separate metatarsals (first and fifth
subequal, shorter than others).
ARTIFICIAL KEY TO THE SPECIES OF THE GENUS ZAPUS
A. Baculum with tip spade-shaped and tip wider than 0.43 mm;
underfur with medullary pattern rectangular, cuticular scales
small; coronoid process of mandible long and slender, angle of
divergence from condyle broad; angle of mandible turned in and
wide; pterygoid fossae wide; skull broad in relation to length;
premolars with crescentine fold on occlusal surface.
_Zapus trinotatus_ p. 385
A´. Baculum with tip lanceolate (not spade-shaped) and tip less
than 0.43 mm wide; underfur with medullary pattern square or
rectangular; but, if rectangular, cuticular scales large;
coronoid process short and broad, angle of divergence from
condyle narrow; angle of mandible turned inward and small to
medium; pterygoid fossae usually narrow; skull not broad in
relation to length; premolars without crescentine fold on
occlusal surface.
B(A´). Baculum less than 5.1 mm in total length; guard hair
averaging 115 micra in diameter; underfur with rectangular
medullary pattern, cuticular scales large; skull small;
incisive foramina shorter than 4.6 mm; condylobasal length
averaging less than 20 mm; length of maxillary tooth-row
averaging less than 3.7 mm; palatal breadth at M3 less than
4.2 mm.
_Zapus hudsonius_ p. 420
B´. Baculum more than 5.1 mm in total length; guard hair averaging
more than 140 micra in diameter; underfur with square medullary
pattern, cuticular scales moderately large; skull large;
incisive foramina longer than 4.7 mm; condylobasal length more
than 21 mm; maxillary tooth-row averaging more than 3.8 mm;
palatal breadth at M3 more than 4.4 mm.
_Zapus princeps_ p. 394
SYSTEMATIC ACCOUNTS OF SPECIES AND SUBSPECIES
=Zapus trinotatus= Rhoads
(Synonymy under subspecies)
_Range._--From southwestern British Columbia southward through western
Washington and Oregon and in the humid coastal district of California
almost to the Golden Gate (see fig. 45).
_Characters of the species_: _External._--Size medium to large (total
length 221 mm to 238 mm); tail longer than head and body (131 mm to 149
mm) and bicolored, brown above, white to yellowish-white below; hind
feet long (31 mm to 34 mm), grayish-white above; back various hues and
tones of ochraceous and tawny; sides paler than back; lateral line
separating sides from ventral surface usually distinct and bright;
ventral coloration white, usually with suffusion of ochraceous; ears
usually dark, sometimes flecked, and usually narrowly edged with color
of sides; guard hairs average 141 microns (133u to 155u) in diameter;
underhair with medullary pigment in narrow, hollow rectangles; cuticular
scales of underhair smaller and more numerous than in other species.
_Baculum._--Size large (total length 6.7 mm to 7.4 mm); base broad (0.7
mm to 0.9 mm); tip broad (0.44 mm to 0.57 mm); spade-shaped in dorsal
aspect and tilted upward, gradually tapering to thin-edged tip; shaft
rounded, straight.
_Skull._--Large, broad and deep in relation to length; pterygoid fossa
broad; anterior ramus of zygomatic process of maxillary relatively
narrow; nasofrontal juncture relatively broad; coronoid process of
mandible elongate. Upper premolars relatively large (averaging .70 mm in
length and .75 mm in width), usually functional, occlusal surface with
labial re-entrant fold forming crescentine loop incompletely enclosing
single central cusp; m3 relatively large, elongated; m1 elongated,
broadly rounded anteriorly.
GEOGRAPHIC VARIATION
There are four subspecies currently recognized, all of which are
confined to the Pacific coastal region of North America (See fig. 45).
The features that vary geographically are external size, color of pelage
(shade and tone of upper parts and tint of lower parts), and dimensions
of certain cranial structures (zygomata, braincase, incisive foramina,
palatal bridge, auditory bullae, and pterygoid fossae).
External size is smallest in the southernmost geographic race (_Z. t.
orarius_) and largest in the northernmost geographic race (_Z. t.
trinotatus_). This decrease in size from north to south is clinal and is
in keeping with Bergman's Rule which postulates that within one species
the smallest individuals occur in the warmer parts of its geographic
range.
[Illustration: FIG. 45. Map showing distribution of _Zapus
trinotatus_.
1. _Z. t. eureka_ 3. _Z. t. orarius_
2. _Z. t. montanus_ 4. _Z. t. trinotatus_]
Coloration of pelage is geographically variable. There is a gradual
change in the color of the pelage from north to south. Animals obtained
in the northern part of the geographic range of _Z. trinotatus_ are
generally darker dorsally (more tawny) with the ventral pelage usually
pure white. Those individuals from the southern part of the geographic
range of _Z. trinotatus_ have the dorsal pelage lighter (more reddish
and yellow-brown) and ventrally the pelage is usually heavily suffused
with reddish-brown. The crania also vary geographically; they are
largest in the northernmost part of the range of the species and
smallest in the southernmost part.
NATURAL HISTORY
_Habitat._--On the Olympic Peninsula, Washington, in 1931 Svihla and
Svihla (1933:132) found this species equally abundant in alpine meadows
near timberline, in open grassy areas, and in tall meadow grass and low
blueberry bushes. All of the mice were in wet marshy places. Bailey
(1936:232) reported that in Oregon, these mice live in meadows, marshes,
under ferns and weeds in the woods, or near mountain brooks and streams.
Taylor (1922:221) found _Zapus_ in moderately moist meadows in the
Hudsonian Life-zone at Mt. Rainier, Washington, and Dice (1932:49) found
them in deciduous forest and in open, grassy, or sphagnum bogs. Dice
records it as common also among the alders and willows in high, open,
grassy parks. Merriam (1897b:223) found _Z. trinotatus_ abundantly in
moist places grown-over with grass or weeds. Grass cuttings two to three
inches long were left in small heaps at feeding sites and indicate the
presence of these mice.
_Behavior._--Svihla and Svihla (1933:131) write that the long tail of
_Z. trinotatus_ is used as a balancing organ when the mouse is in
motion. A tailless mouse, attempting to escape, turned somersaults in
the air and invariably landed on its back; the loss of its tail seemed
to leave the mouse without compensation for the vigorous push of the
hind legs. Dalquest (1948:371) noted that the jumping mouse sometimes
walks on all fours, but ordinarily moves by means of short hops on the
hind feet alone. When startled, jumping mice travel in bounds of six
feet or more at a jump.
_Zapus trinotatus_, according to Bailey (1936:232) and Elliot
(1899:261), is mainly nocturnal but occasionally is active in daylight.
Svihla and Svihla (_op. cit._:132) heard captive animals make squeaking
noises when fighting. On several occasions captive animals made a
drumming noise by rapidly beating the tail against a resonant body such
as the bottom of a tin can.
Concerning hibernation, Bailey (_loc. cit._) remarks that animals of
this species in Oregon, become fat in early autumn and lay down excess
adipose tissue under the skin, over the muscles, and in the abdominal
cavity. Svihla and Svihla (_op. cit._:133) noted that captives from the
Olympic Peninsula, Washington, gained weight in September and October
and became extremely fat. With the additional weight they were more
listless and drowsy, often spending days curled up in the hibernating
position with the head between the hind legs and the long tail curled
completely over the head and body. Warmth aroused the animals to
activity, but when the temperature dropped they again hibernated.
Flahaut (1939:17) reported the discovery on February 23, 1939, at
Henderson Inlet, South Bay, Thurston County, Washington, of two nest
cavities inhabited by jumping mice that were hibernating. The nests,
four inches apart and 30 inches below the surface of the ground, were
approximately five inches in diameter and made of shredded paper. Both
mice were dormant, covered by nesting materials and curled up in the
aforementioned hibernating posture. Dalquest (1948: 371) writes that in
the lowlands of Washington this species disappears by late July but that
in the mountains it remains active until the middle of September. Edson
(1932:56) records an individual taken on April 20 from its place of
hibernation beneath the roots of a decaying stump. This animal quickly
roused in the warm mid-afternoon sun but became dormant again when the
temperature dropped to 45° F. It seems that animals near the end of
hibernation become active on warm days and return to the torpid state on
cold ones.
_Enemies._--Little is recorded concerning enemies of _Z. trinotatus_,
but Bailey (1936:233) lists owls and other nocturnal birds, weasels,
skunks, and badgers as preying on this mouse. Smith and Hopkins
(1937:191) found _Z. t. orarius_ in barn owl pellets obtained in Elk
Valley, Marin County, California.
_Food._--Bailey (_loc. cit._) remarks that in Oregon, these mice feed
mainly on small seeds of grasses, small grains (wheat, barley, oats, and
rye), and other plants. These seeds are obtained by cutting the stems,
drawing the stems down and biting off lower sections until the
seed-laden heads are reached. Bailey (_op. cit._:234) found that
_trinotatus_ utilized also the seeds of the western skunk cabbage.
Near Seattle, Washington, according to Dalquest (_loc. cit._), the
principal food of _Z. trinotatus_ was velvet grass (_Holchus lanatus_),
broad-leaved dock, and the seeds of other grasses. Dalquest reports also
that the fruit of the blackberry (_Rubus macropelatus_) is eaten and
that an occasional jumping mouse has its chin stained a deep purple by
juice from these berries.
_Reproduction._--There is normally a single litter of from four to eight
young per year according to Bailey (_loc. cit._). Newly born young have
been described by Svihla and Svihla (1933:132) as follows: slightly
smaller than newly born harvest mice (_Reithrodontomys m. megalotis_),
average weight .8 grams, hairless (without even vibrissae visible),
pink, eyes closed, ears folded, heads short and stubby, tails long
(longer than those of newly born _Peromyscus_), and bodies surprisingly
small (when compared with newly born _Peromyscus maniculatus_).
=Zapus trinotatus eureka= A. B. Howell
_Zapus trinotatus eureka_ A. B. Howell, Univ. California Publ.,
Zool. 21:229, May 20, 1920.
_Zapus trinotatus trinotatus_, Preble, N. Amer. Fauna, 15:26,
August 8, 1899 (part--the part from Crescent City and Carsons
Camp, Mad River, California).
_Zapus orarius_ Preble, N. Amer. Fauna, 15:29, August 8, 1899
(part--the part from Eureka and Carsons Camp, Mad River,
California).
_Type._--Female, adult, skin and skull, No. 11703, Mus. Vert. Zool.;
Fair Oaks, Humboldt County, California; obtained on August 27, 1910, by
Joseph S. Dixon, original No. 1743.
_Range._--Northwestern coastal region of California, from Russian Gulch
State Park, Mendocino County north to Trinidad, Humboldt County. Zonal
range: humid Transition.
_Description._--Size medium; color dull; back near Ochraceous-Buff with
heavy admixture of black hairs, forming broad dorsal band; sides from
near Ochraceous-Buff to near Ochraceous-Salmon, sometimes with heavy
admixture of black hairs; lateral line usually distinct, sometimes
blending with color of belly and side; ventral surface usually suffused
with color of sides; tail bicolored, dark brown above, white to
yellowish-white below; feet grayish-white above; ears dark, edged with
color of sides; auditory bullae large; pterygoid fossae broad; incisive
foramina relatively short; palatal bridge short; maxillary tooth-rows
relatively short; narrow across zygomata; braincase narrow; interorbital
region narrow; zygomatic arch relatively short.
_Comparisons._--From _Zapus trinotatus trinotatus_, _Z. t. eureka_
differs in: Size smaller; ventral surface with much greater suffusion of
ochraceous; auditory bullae larger; pterygoid fossae relatively broader;
frontal region less inflated; palatal bridge shorter; braincase
narrower; narrow across zygomata; upper tooth-rows shorter.
For comparison with _Zapus trinotatus orarius_ see account of that
subspecies.