Chapter II: Part 2

SKULL.--Some of the structures useful for separating taxonomic entities may have little or no biological significance to the animals in nature. Characters mentioned by me are chosen simply for their significance taxonomically. The zygomata vary in degree of lateral bowing, being widely bowed in _Z. princeps_ and _Z. trinotatus_, and less so in _Z. hudsonius_. Differences in zygomatic breadth owing to the degree of bowing are an aid in differentiating subspecies. The length of the skull from the occipital condyles to the tip of the longest nasal bone is useful in separating _Z. hudsonius_ from _Z. trinotatus_ and _Z. princeps_. The narrowness of the base of the zygomatic process of the squamosal is useful in distinguishing between _Z. hudsonius_ and _Z. princeps_, but shows no variation of subspecific worth. The shape and dimensions of the incisive foramina provide specific and subspecific characters. The position of the anterior margin of the postpalatal notch, in relation to the last molars, provides subspecific characters in _Z. princeps_. In the species _Z. princeps_ the median projection on the inferior ramus of the zygomatic process of the maxillary is absent in some subspecies, small in others, and large in some. Shape and inflation of the auditory bullae, shape of the pterygoid fossae, and shape of the nasals are useful in determining specific and subspecific relationships.

TEETH.--The alveolar length of the upper maxillary tooth-rows aids in distinguishing _Z. hudsonius_ from _Z. princeps_ and _Z. trinotatus_. Nearly parallel versus anteriorly divergent upper tooth-rows is a subspecific difference in _Z. princeps_. Variations in the dimensions of P4 and M1 aid in estimating the relationships of species. The occlusal pattern shows little variation and was of no use in separating species.

NONGEOGRAPHIC VARIATION

A knowledge of variation resulting from age, individual, or secondary sexual differences, as opposed to geographic variation between two or more populations of a single species is important in determining the reliability of taxonomic characters.

The largest population-sample of _Zapus_ available to me for the study of nongeographic variation was 63 individuals from various localities in Keweenaw and Menominee counties, Michigan. Thirty-nine were females and 24 were males. It is on these specimens that this discussion is based.

Age Variation

TEETH.--The teeth provide a valuable standard for age determination in that they wear at a measurable rate. The molars erupt in sequence from front to back, and wear shows first on M1 and last on M3. The peglike permanent P4, of which I have not seen the deciduous precursor, receives wear at the same time that the molars are being worn. Wear proceeds at approximately the same rate in the teeth of both the upper jaws and lower jaws.

In order to be more nearly certain that specimens used in making racial comparisons were comparable as to age, six age-groups were established, from youngest to oldest. These groups were based on the degree of wear on the occlusal surface of the upper cheek-teeth, and are as follows: group 1, in which M1 and M2 have not reached full and equal height and show no occlusal wear, and M3 has not erupted or is just breaking through the alveolus; group 2, in which M1 and M2 have reached full and equal height and show slight wear, and M3 may be almost or quite equal in height to M1 and M2 and, when equal, sometimes shows slight wear; group 3, in which M1 and M2 show wear on all cusps but cusps are visible, and M3 shows slight wear; group 4, in which P4 shows slight wear, M1 has cusps and re-entrant folds between cusps mostly gone, M2 shows considerable wear but re-entrant folds are visible, and M3 has most re-entrant folds and cusps gone; group 5, in which P4 shows considerable wear, M1 has cusps completely worn away, M2 has re-entrant folds and cusps worn away, and M3 lacks occlusal pattern except for one or two lakes; group 6, in which all upper cheek-teeth are without occlusal pattern.

These groupings are based on continuously variable features, and, therefore, when the teeth are at certain stages of wear a specimen is difficult to place in one of two groups.

Age group 1 and 2 include juvenal and subadult animals. Animals of age groups 3 through 6 are considered adult. Individuals of age groups 3 through 5, including as they do the great majority of the adult population, were the only age classes used in measuring geographic variation.

Quimby's (1951:69) data indicate that some mice produce litters at the age of approximately 2 months, when four-fifths grown. Therefore, sexual maturity is not always synonymous with morphological maturity.

MEASUREMENTS OF EXTERNAL PARTS.--Data presented here on _Z. hudsonius_ are those recorded by Quimby (1951) on specimens from Anoka County, Minnesota, and those obtained by me from museum specimens from Menominee and Keweenaw counties, Michigan.

According to Quimby (1951:65-66) the mean length [= body length] for three newly born _Z. hudsonius_ is 24.8 mm (24.0-25.5); at the end of the fourth week of growth the mean length averaged 64.4 mm and at the 13th week 77.6 mm. Rapid growth occurs during the first four weeks, with the mean length increasing approximately 2.6 times the size at birth. After the fourth week of development, growth proceeds at a slower rate; the mean length at 13 weeks is only 3.1 times greater than the mean length at birth.

In specimens assigned to age groups 1 and 2 the length of the body averaged 70 and 74.8 mm, respectively. The individuals of both groups are less than 13 weeks old if we assume that growth proceeds at the same rate in Michigan as it does in Minnesota.

In the specimens from Michigan of age groups 3, 4, 5, and 6 the average length of the body is 80.9, 83.7, 89.0, and 83.6, respectively.

According to Quimby (_loc. cit._), the average length of the tail for three _Z. hudsonius_ at birth was 9.2 mm. (8.5-10.0). During the first four weeks of development the tail grew rapidly and reached an average length of 92.0 mm, which was 10 times the length at birth. By the end of 13 weeks of development the average length of the tail for these three individuals was 119.6 mm or 12 times the average length at birth. The most rapid growth was early in development: 80 per cent of the growth of the tail occurred during the first month, after which growth proceeded at a much slower rate.

Quimby (_loc. cit._) records an average dimension of 4.7 mm (4.5-5.0) for the length of the hind foot in three newly born _Z. hudsonius_. The hind foot grew rapidly in length and by the fourth week had increased 5.6 times in its length and averaged 26.3 mm. Growth was much less rapid from the fourth to the thirteenth week when the hind foot averaged 27.7 mm, only five per cent more than in mice four weeks old. Assuming the average length of the hind foot of the adults to be 29.0 mm, the hind foot in individuals 13 weeks old is 96 per cent of the adult size.

According to Quimby (_loc. cit._), the pinna of the ear at birth is small and folded over the external auditory meatus. The length of the ear increases proportionately more (29 per cent) than any other external dimension after the first four weeks of growth.

If the average length of the ear (measured from the crown) of adults is 14.7 mm, the animals from Michigan in age groups 1 and 2 are 91.8 per cent and 96.5 per cent as large as adults.

TABLE 1.--Average Dimensions (in Millimeters) for Specimens of
Z. h. hudsonius of Various Ages (Specimens from Michigan).

==============+=======+=======+=======+=======+=======+=======
Age groups | 1 | 2 | 3 | 4 | 5 | 6
--------------+-------+-------+-------+-------+-------+-------
No. examined | 4 | 13 | 33 | 12 | 3 | 3
--------------+-------+-------+-------+-------+-------+-------
Body | 70.0 | 74.8 | 80.9 | 83.7 | 89.0 | 83.6
--------------+-------+-------+-------+-------+-------+-------
Tail | 113.8 | 118.5 | 122.9 | 125.0 | 125.0 | 118.3
--------------+-------+-------+-------+-------+-------+-------
Hind foot | 28.8 | 28.6 | 28.9 | 29.1 | 28.9 | 29.3
--------------+-------+-------+-------+-------+-------+-------
Ear | 13.5 | 14.2 | 14.7 | 14.8 | 15.0 | 14.3
--------------+-------+-------+-------+-------+-------+-------

From these data, concerning growth of external parts, it seems that: growth is most rapid during the four weeks following parturition; specimens from Michigan, assigned to age groups 1 and 2 on the basis of tooth wear, are less fully developed and probably younger than mice from Minnesota, with a known age of 13 weeks; individuals with sufficient wear on the teeth to be placed in age group 3, if they were obtained in the late fall, may be young from the first litters of the year or, if they were obtained in early spring, may be at least one year old; individuals in age groups 4, 5, and 6 are at least one year old.

SKULL.--The post-embryonic development of the skull is rapid. Animals in age groups 1 and 2 have skulls which average more than 80 per cent of the size that is here considered adult (an average size obtained from age groups 3, 4, and 5). The actual increase in size of certain cranial elements for various age groups is given in table 2.

In age group 1 the rostrum is relatively short as it is in _Neotoma micropus_ (J. A. Allen, 1894:235) and juveniles of _Peromyscus truei_ (Hoffmeister, 1951:7). The rostrum lengthens rapidly and there is a general increase in actual and relative size of the entire preorbital region; the increase after age group 3 is slower and of lesser magnitude. Changes with age in the size of the braincase are slight. In age group 1 the average depth of the braincase is 99.6 per cent of the adult size; the average breadth of the braincase is 98 per cent of the adult size, and the average width across the mastoid region is 96.4 per cent of the adult size. These dimensions indicate that the braincase reaches full size early. The zygomatic arch, however, undergoes change with age; there is a gradual increase in breadth owing to lateral bowing and a gradual lengthening which is in keeping with a general elongation of the skull anterior to the braincase.

The incisive foramina in age group 1 are short (4.0 mm), broad (2.2 mm in the middle), and taper to a point at each end. In age group 2 the foramina have elongated (4.2 mm) and are less pointed posteriorly, but there is no change in breadth. In age groups 3, 4, 5, and 6 the foramina become progressively longer (4.5 mm in age group 6), have a relatively constant breadth (2.2 mm), and become more nearly truncate anteriorly.

TABLE 2.--Average and Extreme Measurements (in Millimeters) of
Skulls of Six Age-groups in Specimens of Zapus hudsonius
from Michigan.

===============+============+============+============
Age groups | 1 | 2 | 3
---------------+------------+------------+------------
Number | | |
examined | 4 | 13 | 33
| | |
Occipitonasal | 20.5 | 21.2 | 22.0
length | 20.0 21.2 | 20.8 21.8 | 21.5 23.2
| | |
Mastoid | 9.8 | 10.04 | 10.12
breadth | 9.7 10.0 | 9.6 10.4 | 9.5 10.5
| | |
Length of | 8.07 | 9.02 | 9.07
zygomatic arch | 8.0 8.2 | 8.5 9.3 | 8.5 9.4
| | |
Breadth of | 3.36 | 3.33 | 3.37
palate at P4 | 3.3 3.5 | 3.1 3.4 | 3.1 3.8
| | |
Breadth of | 2.4 | 2.55 | 2.66
palate at M3 | 2.3 2.6 | 2.3 2.7 | 2.3 3.2
| | |
Palatal | 8.67 | 8.98 | 9.38
length | 8.4 9.1 | 8.8 9.2 | 9.3 9.8
| | |
Distance from | | |
incisors to | 8.53 | 8.98 | 9.08
postpalatal | 8.4 8.7 | 8.5 9.5 | 9.0 9.8
notch | | |
| | |
Interorbital | 4.25 | 4.19 | 4.2
breadth | 4.2 4.3 | 4.0 4.4 | 4.0 4.4
| | |
Average length | | |
of upper | 3.2 | 3.2 | 3.21
molar series | 3.2 3.4 | 3.2 3.4 | 2.9 3.5
| | |
Breadth of | 9.5 | 9.58 | 9.61
braincase | 9.3 9.7 | 9.2 9.7 | 9.1 10.0
| | |
Zygomatic | 10.33 | 10.49 | 10.55
breadth | 10.0 10.7 | 10.4 10.9 | 10.1 11.2
| | |
Condylobasal | 16.9 | 18.33 | 18.80
length | 16.6 17.1 | 17.4 19.2 | 18.2 19.5
---------------+------------+------------+------------

===============+============+============+============
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.

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.

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.

_Remarks._--Howell (1920:230), without having examined the material, provisionally referred specimens from Requa and Crescent City, Del Norte County, California, to _Z. t. eureka_. I have studied this material and find the specimens to be intermediate between _Z. t. trinotatus_ and _Z. t. eureka_ in cranial characters (zygomatic breadth, interorbital width, and breadth of braincase), but nearer _Z. t. trinotatus_ in coloration (absence of ochraceous suffusion ventrally). They are here referred to _Z. t. trinotatus_. The zone of intergradation between _Z. t. trinotatus_ and _Z. t. eureka_ seems to extend from Requa, California, north to Gold Beach, Oregon, where other specimens intermediate between these two subspecies, have been obtained. These individuals are also referred to _Z. t. trinotatus_ on the basis of cranial features and color.

_Specimens examined._--Total, 42, all from California, distributed as follows: _Humboldt Co._: Trinidad, 4 (SDM); Carsons Camp, Mad River, 3 (USBS); 3 mi. W Arcata, 5 (MVZ); _7-3/10 mi. E Bayside_, 1 (MVZ); _12 mi. S Korbel, on Maple Creek_, 2 (MVZ); _Falk_, 1 (MVZ); Carlotta, 1 (MVZ); _F. B. Summer Redwoods, S Eureka_, 1 (MVZ); _Maple Creek, 1 mi. W junction Mad River_, 12 (MVZ). _Mendocino County_: Mendocino City, 1 (MVZ); Albion River, 1/3 mi. E MacDonalds Ranch, 1 (MVZ); Russian Gulch State Park, 10 (MVZ).

_Marginal records._--California: Trinidad; Russian Gulch State Park; Albion River, 1/3 mi. E MacDonalds Ranch; Mendocino City; Carlotta.

=Zapus trinotatus montanus= Merriam

_Zapus trinotatus montanus_ Merriam, Proc. Biol. Soc. Washington,
11:104, April 26, 1897; Bailey, N. Amer. Fauna, 55:234,
August 29, 1936.

_Zapus montanus_, Preble, N. Amer. Fauna, 15:28, August 8, 1899.

_Type._--Female, adult, skin and skull; No. 79863, U. S. Nat. Mus., Biol. Surv. Coll.; Crater Lake, Klamath County, Oregon; obtained on August 19, 1896, by Edward A. Preble, original No. 1388.

_Range._--From Crater Lake, Klamath County, Oregon, northward along the Cascade Range into Hood River County, Oregon. Zonal range: Transition and Canadian.

_Description._--Size medium; back near Ochraceous-Buff with admixture of black hair, resulting in a grizzled, broad, dorsal band; sides lighter than back, from near Ochraceous-Buff to near Pinkish-Cinnamon, and lined with black hair; lateral line distinct; underparts usually pure white, sometimes with slight suffusion of ochraceous on lower throat and upper chest; tail bicolored, brown above and yellowish-white below; ears dark, sometimes flecked with ochraceous, edged with yellowish-white; feet grayish-white above; braincase relatively narrow; zygomata relatively short; condylobasal length short; mastoid region relatively narrow; palatal bridge short; auditory bullae large; frontal region inflated; pterygoid fossae relatively narrow.

_Comparison._--From _Zapus trinotatus trinotatus_, _Z. t. montanus_ differs as follows: Size averaging smaller; sides more ochraceous, fewer black hairs; upper parts duller; skull smaller; zygomatic arch shorter, braincase relatively narrower; frontal region more inflated; pterygoid fossae relatively narrower; zygomata narrower.

_Remarks._--The systematic status of _Z. t. montanus_ has been in doubt. Several workers, for example, Howell (1920:227) and Preble (1899:28), considered it to be a species, and others (Merriam, 1897a:104, Bailey, 1936:234) considered it to be a subspecies of _Z. trinotatus_. _Z. montanus_ is here considered to be a subspecies of _Z. trinotatus_, because of the agreement of the two in size and shape of the baculum, diameter and pigment pattern of the hair, and the over-all proportions of the skull. In addition, animals from intermediate geographic areas are available and show actual intergradation.

Intergradation has been noted in specimens from North Santiam River, 3400 ft., Oregon. In color, in length of incisive foramina, in breadth of braincase, and in width of zygomata these specimens are intermediate between _Zapus trinotatus montanus_ and _Z. t. trinotatus_, but in the sum-total of characters they are referable to the former. Specimens from Lost Creek R. S., 10 mi. SE McKenzie Bridge, are intermediate in color between _Z. t. trinotatus_ and _Z. t. montanus_; they are referable to _Z. t. montanus_. The animals available from Brooks Meadow, 4300 ft., 9 mi. ENE Mt. Hood and the one from Mt. Hood, in color, in length of incisive foramina, and in mastoid width, closely approach _Z. t. trinotatus_ from Skamania County, Washington, but in the sum-total of characters are nearest _Z. t. montanus_ and are here referred to _montanus_.

_Specimens examined._--Total, 35, all from Oregon, distributed as follows: _Deschutes County_: Tumalo Creek, 15 mi. W Bend, 6100 ft., 3 (MVZ). _Douglas Co._: Diamond Lake, 1 (USBS). _Hood River Co._: Brooks Meadow, 4300 ft., 9 mi. ENE Mt. Hood, 10 (MVZ); _Mt. Hood_, 1 (USBS). _Klamath Co._: _Crater Lake_, 3 (MVZ); _1/2 mi. N Government Camp, 6700 ft., Munson Valley, Crater Lake Nat'l Park_, 2 (MVZ); east slope Cascade Divide, 6400 ft., Crater Lake Nat'l Park, 2; Anna Creek, Mt. Mazama, 6000 ft., 2 (USBS). _Lane Co._: Lost Creek R. S., 10 mi. SE McKenzie Bridge, 6 (USBS); _Three Sisters, Alder Springs, 4300 ft._, 2 (USBS). _Linn County_: North Santiam River, 3400 ft., 3 (MVZ).

_Marginal records._--Oregon: Brooks Meadow, 4300 ft., 9 mi. ENE Mt. Hood; Tumalo Creek, 15 mi. W Bend, 6100 ft.; Anna Creek, Mt. Mazama, 6000 ft.; east slope Cascade Divide, 6400 ft., Crater Lake Nat'l Park; Diamond Lake; North Santiam River, 3400 ft.

=Zapus trinotatus orarius= Preble

_Zapus orarius_ Preble, N. Amer. Fauna, 15:29, August 8, 1899.

_Zapus pacificus_ Merriam, Proc. Biol. Soc. Washington, 11:104,
April 26, 1897 (part--the part from Point Reyes, Marin County,
California).

_Zapus trinotatus orarius_, Hooper, Miscl. Publ. Mus. Zool. Univ.
Michigan, 59:67, January 12, 1944.

_Type._--Male, adult, skin and skull, No. 250, collection of E. A. and O. Bangs (now in Mus. Comp. Zool.); Point Reyes, Marin County, California; obtained on May 14, 1893, by C. A. Allen, original No. 618.

_Range._--Southern and western Marin County, California. Zonal range: Upper Sonoran areas that are moist yet safe from continuous inundation.

_Description._--Size small; back dark ochraceous, usually overlaid with black hairs forming broad dorsal band; side lighter than back with admixture of black hairs; lateral line distinct, usually bright, near Ochraceous-Buff; under parts strongly suffused with ochraceous; tail bicolored, white to yellowish-white below and dark brown above; feet grayish-white above; ears dark, edged with yellowish-white or tan; skull small; zygomata narrow; braincase narrow; maxillary tooth-rows short; interorbital region narrow; incisive foramina short; palatal bridge relatively long; mastoid region relatively broad; occipitonasal length short.

_Comparison._--From _Zapus trinotatus eureka_, _Z. t. orarius_ differs in: Size smaller; color, dorsally and laterally, brighter, more ochraceous; skull averaging smaller in all measurements taken except length of palatal bridge, where it averages longer; auditory bullae smaller, less inflated; pterygoid fossae narrower.

_Remarks._--Preble (1899:30) named this jumping mouse as a full species. Included in the specimens examined were animals from Eureka and Mad River, Humboldt County, California. Howell (1920:231) retained _Z. orarius_ as a full species but restricted its range to Marin County, California, and referred material from northern California, including the animals from Eureka and Mad River, to a new subspecies (_eureka_) of the species _Z. trinotatus_. Howell (_loc. cit._) suggested that _Z. orarius_ had its closest affinity with _Z. t. eureka_ but remarked that intergrading material was not available. Hooper (1944:68) arranged _Z. orarius_ as a subspecies of _Z. trinotatus_ and suggested that intergrades could be expected from geographically intermediate areas, for example, northern Sonoma County, California.

Although animals from intermediate geographic areas still are not available to show actual intergradation, I concur with Hooper (_loc. cit._) and arrange _Z. orarius_ as a subspecies of _Z. trinotatus_. The close relationship of _Z. orarius_ to _Z. trinotatus_ is evident; certain diagnostic characters, held in common, are the shape and size of the os penis, the diameter and pigment pattern of the hair, and the general configuration of the skull.

Interbreeding in the wild between _Z. t. orarius_ and _Z. t. eureka_ probably does not take place, because these subspecies are separated by terrain unsuited to jumping mice.

_Specimens examined._--Total, 29, all from California, distributed as follows: _Marin County_ (MVZ): 3 mi. W Inverness, 300 ft., 14; _5 mi. NNE Point Reyes Lighthouse_, 12; _W end Elk Valley, 10 ft._, 1; West Portal, Fort Barry, 2.

_Marginal records._--California: 3 mi. W Inverness, 300 ft.; West Portal, Fort Barry.

=Zapus trinotatus trinotatus= Rhoads

_Zapus trinotatus Rhoads_, Proc. Acad. Nat. Sci. Philadelphia,
1894:42, January 15, 1895.

_Jaculus hudsonius_, Baird, Repts. Expl. and Surv. 111, 8 (pt. 1):
433, July 14, 1858 (part--the part from Washington).

_Zapus hudsonius_, Coues, Bull. U. S. Geol. and Geog. Surv. of the
Territories, 2nd ser., No. 5:260, 1877 (part--the part from
Steilacoom [Pierce County], Washington).

_Zapus imperator_ Elliot, Field Columbian Mus., publ. 30, zool.
ser., 1:228, February 1, 1899, type from Siegs Ranch, Elwah River,
Clallam County, Washington.

_Zapus princeps trinotatus_, Dalquest, Univ. Kansas Publ. Mus. Nat.
Hist., 2:371, April 9, 1948.

_Type._--Male, adult, skin and skull, No. 360, S. N. Rhoads Coll.; Lulu Island, mouth of Frazer River, British Columbia; obtained on May 31, 1892, by S. N. Rhoads (type in Philadelphia Acad. Nat. Sci.).

_Range._--Pacific coastal region from Requa, Del Norte County, California, north in Oregon west of the Cascades, and in Washington including the Cascades; to southwestern British Columbia.

_Description._--Size large; back from near Ochraceous-Buff to near Tawny with admixture of black hair forming broad dorsal band; sides lighter than back from near Ochraceous-Buff to near Tawny; lateral line usually distinct; belly white, sometimes with faint suffusion of ochraceous on lower throat and upper chest; tail bicolored, brown above, white to yellowish-white below; ears dark, sometimes flecked with color of sides, edged with ochraceous; feet grayish-white above; palatal bridge relatively short; incisive foramina relatively long; condylobasal region long; zygomatic width great; braincase relatively broad; distance from incisors to postpalatal notch relatively great.

_Comparisons._--For comparisons with _Zapus trinotatus montanus_ and _Zapus trinotatus eureka_ see accounts of those subspecies.

_Remarks._--This subspecies retains most of its diagnostic characters throughout nearly all parts of its geographic range. Intergradation occurs between _Z. t. eureka_ and _Z. t. trinotatus_ in extreme southwestern Oregon and northwestern California (see account of _Z. t. eureka_). Intergrades between _Z. t. montanus_ and _Z. t. trinotatus_ have been commented on in the account of _Z. t. montanus_. Specimens from Eugene, Oregon, according to Bailey (1936:232), show affinity to _Z. t. montanus_ but are considered by him to be _Z. t. trinotatus_.

_Specimens examined._--Total, 238, distributed as follows:

BRITISH COLUMBIA: Alta Lake, on Pac. Gt. Eastern Ry., 2600 ft., 5 (MVZ); Okanagan, 1 (FM); _Vedder Crossing_, 4 (1 MVZ, 3 PM); _Chilliwack Valley_, 2 (NMC); 18 mi. S Chilliwack, 1 (MVZ); Cultus Lake, 2 (NMC); _Lihumption Park, 4500-4800 ft._, 12 (NMC); _Seymour Mtn., 4000 ft._, 8 (1 MVZ, 7 PM); _Cariboo_, 2 (FM); _Sumas_, 8 (1 MVZ, 7 FM); Huntingdon, 40 (NMC); _Parnassus Creek, Black Tusk Meadow, 5200 ft._, 1 (PM); _Howe Sound, Brackendale_, 2 (NMC); Stanley Park, Vancouver, 1 (PM); _Allison Pass, Manning Park_, 1 (PM); Manning Park, 2 (PM).

CALIFORNIA: _Del Norte Co._: Crescent City, 11 (6 FM, 5 USBS); Requa, 4 (FM).

OREGON: _Benton County_: _3 mi. N Corvallis_, 2. _Clatsop County_: Old Fort Clatsop, 100 ft., 11 (MVZ); 7-1/2 mi. S Cannon Beach, 50 ft., 1 (MVZ). _Columbia County_: 7 mi. SE Rainier, 100 ft., 11 (MVZ). _Curry County_: Gold Beach, 3 (FM). _Douglas County_: Gardiner, 7 (5 MVZ, 2 FM). _Lane County_: Sutton Lake, 6 mi. N Florence, 1 (MVZ). _Lincoln County_: _Delake_, 3 (2 MVZ); Newport, 2 (MVZ). _Multnomah County_: Portland, Council Crest, 950 ft., 1 (MVZ). _Tillamook Co._: _Tillamook_, 1 (MVZ); _9 mi. S Tillamook_, 1 (MVZ); Netarts, 3 (SDM); Blaine, 3 (MVZ). _Washington County_: 18-1/2 mi. NW Portland, 1300 ft., 5 (MVZ).

WASHINGTON: _Clallam County_: Deer Lake, 3800 ft., 3. _Clarke County_: _3-1/2 mi. E and 1-1/2 N Amboy, 3500 ft._, 3 (MVZ); _1-1/2 mi. ENE Amboy, 3500 ft._, 13 (MVZ); 3-1/2 mi. E and 5 mi. N Yacolt, 500 ft., 1 (MVZ); _1-1/2 mi. W Yacolt, 800 ft._, 11 (MVZ). _Cowlitz County_: _6 mi. NE Kelso_, 4 (MVZ); _4 mi. E mouth Kalama River_, 5 (MVZ). _King County_: Lakeridge Tract, S end Forest Ave., Lake Washington, 2 (MVZ); Seattle 2 (MVZ); Snoqualmie Pass, 5 (MVZ). _Mason County_: Potlatch, 2 (MVZ). _Pacific County_: _1-1/2 mi. N Chinook, 10 ft._, 1 (MVZ); 3-1/2 mi. SE Chinook, 10 ft., 5 (MVZ). _Pierce Co._: 5 mi. E Tacoma, 4 (MVZ); Puyallup, 3 (1 MVZ, 2 FM); Mt. Rainier, 1 (MVZ); 3 mi. E Ashford, 1 (LMH). _Skamania County_: Ice Caves, 2800 ft., 5 mi. WSW Guler, 1 (MVZ). _Thurston County_: Boston Harbor, 5 (CAS). _Wahkiakum County_: 4 mi. E Skamokawa, 5 (MVZ). _Whatcom County_: Baker Lake, 2 (MVZ).

_Marginal records._--British Columbia: Okanagan; Manning Park. Washington: Baker Lake; Snoqualmie Pass; Mt. Rainier; Ice Caves, 2800 ft., 5 mi. WSW Gulch. Oregon: Portland, Council Crest, 950 ft. California: Requa; Crescent City. Oregon: Gold Beach; Gardiner; Sutton Lake, 6 mi. N Florence; Newport; Netarts; Old Fort Clatsop, 100 ft. Washington: 3-1/2 mi. SE Chinook, 10 ft.; Deer Lake, 3800 ft. British Columbia: Stanley Park, Vancouver; Alta Lake, 2600 ft.

=Zapus princeps= Allen

(Synonymy under subspecies)

_Range._--The Rocky Mountains region from Yukon south into Arizona and New Mexico; westward through eastern Oregon and through the Cascades and Sierra Nevada of California; eastward in the northern Great Plains to extreme eastern parts of the Dakotas (see fig. 46).

_Characters of the species_: _External._--Size medium to large (total length 216 mm to 247 mm); tail longer than head and body (129 mm to 148 mm) and bicolored, pale brown to grayish-brown above, white to yellowish-white below; hind feet long (31 mm to 34 mm), grayish-white above; back variable from yellowish-gray to salmon-brown and ochraceous; sides paler than back; lateral line usually present but sometimes indistinct or entirely absent (when present usually clear Ochraceous-Buff); ventral coloration white, usually suffused with ochraceous; ears usually dark, sometimes flecked and usually narrowly edged with light color; guard hairs average 142 microns (130u to 168u) in diameter; underhair with medullary pigment in form of hollow squares; cuticular scales of underhair larger and fewer than in other species.

_Baculum._--Size medium (total length 5.6 mm to 6.6 mm); base moderately broad (0.7 mm to 0.8 mm); tip narrow (0.26 mm to 0.31 mm) rounded and dished out in dorsal aspect, blunted; shaft rounded, slightly sinusoidal, recurved at tip.

_Skull._--Large, not exceptionally broad and deep in relation to length; rostrum broad but tapering; pterygoid fossa moderately narrow; anterior ramus of zygomatic process usually broad; incisive foramina usually broadly rounded and elongate; auditory bullae usually moderately inflated; coronoid process of mandible relatively short. Upper premolars of medium size (averaging .55 mm in length and .50 mm in breadth), sometimes functional, with occlusal surface normally divided by single shallow re-entrant fold; m1 relatively short, narrow anteriorly.

Guide to subspecies

1. _Z. p. cinereus_ 7. _Z. p. oregonus_
2. _Z. p. curtatus_ 8. _Z. p. pacificus_
3. _Z. p. idahoensis_ 9. _Z. p. princeps_
4. _Z. p. kootenayensis_ 10. _Z. p. saltator_
5. _Z. p. luteus_ 11. _Z. p. utahensis_
6. _Z. p. minor_]

GEOGRAPHIC VARIATION

There are 11 subspecies recognized, most of which are in the mountains of the western United States and southwestern Canada. There is geographic variation in color, relative proportions of external parts (tail, hind feet, head, and body), and shape and size of the skull.

Three basic types of coloration occur in _Z. princeps_, as pointed out by Hall (1931:9). Yellow-sided dark-backed jumping mice exemplified by _kootenayensis_, _idahoensis_, and _utahensis_ are found to the eastward in the Rocky Mountains. Reddishbrown-sided, brown-backed jumping mice typified by _luteus_ and _pacificus_ are found to the westward in the Sierra Nevada and in New Mexico and Arizona; mice with yellowish-buff or pinkish-buff-sides and light backs are the subspecies, _cinereus_, _curtatus_, and _oregonus_, that occur in the intervening Great Basin.

External dimension as a whole decreases from north to south, although not uniformly. For example, the smallest individuals are of the southernmost geographic subspecies (_Z. p. luteus_), but the largest are of the subspecies (_Z. p. utahensis_) that is near the geographic center of the range for the species. In the skull there is geographic variation in the length and shape of the zygomata, size and shape of the incisive foramina, alignment of maxillary tooth-rows, size and shape of auditory bullae, position of the postpalatal notch in relation to M3, and the presence or absence and size of the medial projection on the inferior ramus of the zygomatic process of the maxillary.

NATURAL HISTORY

_Habitat._--_Zapus princeps_ occurs most commonly adjacent to streams where grasses and herbs are in lush growth. It frequents mountain meadows neighboring small streams and is often taken from alder, aspen, or stands of willow, where the moist ground supports a heavy undergrowth of herbs. Davis (1939:330) found these mice in heavy herbage along a small stream bordered by quaking aspen near Victor, Teton County, Idaho. They were found along streams bordered by willow, rose, alder, huckleberry, sedges, and herbs of various kinds at Alturas Lake, Mill Creek, and at the head of the Pahsimeroi River. Linsdale (1938:195) found jumping mice in the Toyabe Mountains, Nevada, near the streamsides or in seepy areas close to the streams where associated vegetation included rose, willow, wild peach, sage, grasses, and herbs. In the Uinta Mountains, Utah, R. D. Svihla (1931:264) obtained them from willows along streams in mountain parks. Borell and Ellis (1934:37) in the Ruby Mountains, Nevada, found jumping mice to be common in heavy vegetation along streams. Louise Kellogg (1916:369) obtained jumping mice in northern California; all were near water, in grassy meadows, or under alders where vegetation was dense.

_Zapus princeps_ is locally abundant, but its numbers seem to vary considerably from year to year as well as seasonally. Early autumn, when young of the year are abroad, seems to be the period of greatest abundance. Moore (1928:154) remarks that runways were plainly marked and well strewn with four-inch pieces of brome-grass. Davis (1939:334) notes that _Z. princeps_ has runways, and found that sections, four inches long, of cut grass piled in runways was good evidence of the presence of the mouse.