BY
E. RAYMOND HALL AND KEITH R. KELSON
IN preparing maps showing the geographic distribution of North American
lagomorphs, some conflicting statements in the literature have led us to
examine the pertinent specimens of the Florida cottontail and the
Audubon cottontail with results as given below. The study here reported
upon was aided by a contract between the Office of Naval Research,
Department of the Navy, and the University of Kansas (NR 161–791).
Unless otherwise indicated, catalogue numbers are of the United States
National Museum and most of the specimens are in the Biological Surveys
collection of the Fish and Wildlife Service. Grateful acknowledgment is
made to persons in charge of the collections for permission to use the
collections under their charge.
Sylvilagus floridanus similis Nelson
1907. Sylvilagus floridanus similis Nelson, Proc. Biol. Soc.
Washington, 20:82, July 22.
Some confusion has existed concerning the subspecific identity of the
Florida cottontail in Nebraska because of the way in which Nelson
recorded specimens in his "The Rabbits of North America" (N. Amer.
Fauna, 29:fig. 11, and pp. 169–174, August 31, 1909). He (op.
cit.:174) listed the following specimens under the western subspecies,
S. f. similis: Two topotypes (Nos. 87784 and 18738/25532) and of
course the type; the specimen (No. 116288) from the Snake River [= Snake
Creek of maps], 11 mi. NW Kennedy; two from Neligh (126074 and 151438);
and one (probably 18680/25410) from Kennedy. But, he listed (op.
cit.:172) under S. f. mearnsi, the eastern subspecies, a specimen
(10721) from Brownlee, and two from Kennedy. One of the two from Kennedy
probably was the one that is recorded in the files of the U.S. Fish and
Wildlife Service as "identified by Cary. spec. in Univ. Nebraska". The
other, or third, specimen from Kennedy, we judge, did not exist at all
but was recorded by Nelson because a card in the reference file, under
Kennedy, Nebraska, in addition to No. 18680/25410, carried a second
entry, a number 3471X. The latter is the X-catalogue number of specimen
No. 116288 from the Snake River! The X-catalogue is used in place of a
field catalogue for specimens sent to the mammal collection of the
United States Fish and Wildlife Service, by persons who do not keep
regular field numbers of their own. It seems that Nelson prepared (or
had prepared) his lists of specimens, at least in part, from cards
rather than from the labels on the specimens themselves. Some further
confusion as to names that Nelson intended to apply to cottontails in
Nebraska resulted from the fact that his map (op. cit.:fig. 11)
indicated that the localities mentioned above for S. f. mearnsi were
within the geographic range of S. f. similis.
Our comparison of each of the Nebraskan specimens with specimens of S.
f. mearnsi in comparable pelage from Iowa and with the type and
topotypes of S. f. similis reveals that each of the specimens of which
catalogue numbers are given above is clearly referable to Sylvilagus
floridanus similis.
Because some mammalogists have suspected that intergradation between
Sylvilagus floridanus similis and Sylvilagus nuttallii grangeri
occurs along the eastern base of the Rocky Mountains, we have examined
specimens which may throw light on this matter.
From S. f. similis (holotype and three topotypes), S. n. grangeri
(eight practical topotypes from Redfern, South Dakota) differ as
follows: Throat patch darker; hind foot shorter; ear (dry) from notch
longer; rostrum narrower; posterior extension of supraorbital process
enclosing a longer and wider space between it and the braincase;
superior border of premaxilla straight in profile instead of convex
dorsally; tympanic bullae more inflated; external auditory meatus larger
(diameter of the meatus more, instead of less, than crown length of
upper molars); posterior border of palate without, instead of with,
spine.
Specimens of the two species from places as near each other as extreme
southeastern Montana (S. f. similis from Boxelder Creek, Capitol and
the Little Missouri River) and Devils Tower, Wyoming (S. n. grangeri),
seem not to differ in the length of the hind foot and the ear and in the
color of the spot on the chest. Also, the presence or absence of the
spine on the posterior margin of the palate is subject to individual
variation in these specimens but the other cranial differences,
mentioned above, still are apparent. These same cranial differences are
readily apparent between specimens of the two species taken only five
miles apart in eastern Wyoming (for the precise localities, see the
following paragraph). It is concluded, therefore, that S. f. similis
and S. n. grangeri do not inter-grade along the eastern base of the
Rocky Mountains.
Data on specimens from Laramie County in eastern Wyoming show that S.
f. similis is a heavier animal than S. n. grangeri and also that
similis molts earlier. For example, an adult female (K.U. No. 15936)
taken on July 13, 1945, three miles east of Horse Creek P.O., 6400 ft.,
weighed 1374 grams and is in fresh pelage, whereas an adult female of
S. n. grangeri (K.U. No. 15935), taken on July 17, 1945, two miles
west of Horse Creek P.O., 6600 ft., weighed only 1149 grams, and still
has some of the worn winter pelage on the upper parts.
Sylvilagus floridanus holzneri (Mearns)
1896. Lepus sylvaticus holzneri Mearns, Proc. U.S. Nat. Mus.,
18:554, June 24.
1904. Sylvilagus floridanus holzneri, Lyon, Smithsonian Miscl.
Coll., 45:336, June 15.
Examination of cottontail rabbits from Arizona in the Biological Surveys
Collection and the United States National Museum indicates that
Sylvilagus audubonii can be distinguished from Sylvilagus nuttallii
and Sylvilagus floridanus by the larger (more inflated) tympanic
bullae. Topotypes of Sylvilagus nuttallii pinetis and other specimens
from Alpine, Mt. Thomas, Springerville, the Prieto Plateau at 9000 feet
on the south end of the Blue Range, and the Tunitcha Mountains are
characterized by a posteriorly pointed supraoccipital shield and a long,
wide space between the braincase and the posterior extension of the
supraorbital process. The cottontails with equally small tympanic bullae
from more western and more southern localities are referable to
Sylvilagus floridanus holzneri on the basis of a posteriorly truncate
or emarginate supraoccipital shield and a narrower and shorter space
(usually a "foramen") between the braincase and the posterior extension
of the supraorbital process. In S. f. holzneri the posterior end of
the posterior process fuses with the braincase whereas the posterior end
of this process in Arizonan specimens of S. n. pinetis merely lies
against the braincase or projects free of it. In specimens from Arizona
the difference in shape of the posterior border of the supraoccipital
shield and the difference in size of the space between the braincase and
the posterior extension of the supraorbital process are the only
differences of taxonomic worth found by us. Many other features of the
skull, of color of pelage, and of size of external parts all fell within
the range of individual variation of a series of specimens from one
locality.
Specimens from the following localities in Arizona are referable to
Sylvilagus floridanus holzneri (Mearns).
Hualpai Mts., Nos. 117461, 117462, 117488, 117490, 117495, 227735,
and 227832; Ft. Whipple, No. 214157; Prescott, No. 34667/46752;
Mayer, No. 247495; Reynolds Creek Ranger Station, Sierra Ancha
Mts., Gila Co., No. 247734; Fish Creek, Tonto National Forest, 2000
ft., No. 212833; north base Mt. Turnbull, 4500 ft., No. 214339; Ash
Creek, 6100 ft., Graham Mts., No. 204363; Pinery Canyon, 7500 ft.,
Chiricahua Mts., No. 247953; Thomas Cañon, 2 mi. E Baboquivari
Mts., No. 244420; Pine Springs, 15 mi. south of Colorado Cañon, No.
2425 Amer. Mus. Nat. Hist. On December 4, 1950, we removed the
skull of No. 2425 to more certainly ascertain the identity of the
individual.
The specimens listed above include those that Nelson (N. Amer. Fauna,
29:211, August 31, 1909) listed from the Hualpai Mountains, Pine
Springs, and Prescott under the name Sylvilagus nuttallii pinetis.
Nelson (op. cit.:Pl. X, fig. 2) figured one of these skulls from the
Hualpai Mountains as S. n. pinetis and the cranial measurements (op.
cit.:201) that he records for S. nuttallii pinetis likewise are of
these same specimens of Sylvilagus floridanus holzneri. Nelson's
description (op. cit.:207–210) seems to have been affected by the
erroneous (as we see the matter) inclusion of these specimens of S. f.
holzneri in the materials identified by him as Sylvilagus nuttallii
pinetis.
The specimens so far mentioned from Arizona can be identified with ease.
The identification becomes difficult, however, when the holotype of S.
f. holzneri, from the Huachuca Mountains, is examined. The difficulty
results from the holotype having a barely detectable emargination in the
posterior border of the supraoccipital shield. In this respect the
holotype is intermediate between S. f. holzneri (as known by specimens
from more western localities in Arizona) and S. n. pinetis from the
White Mountains to the northward. As noted above, S. f. holzneri has a
deep notch and S. n. pinetis has none. This intermediacy of the
holotype supports the possibility, mentioned by Nelson (op. cit.:200),
that intergradation occurs between S. f. holzneri and S. n. pinetis.
Additional evidence, however, is against this possibility; the notch in
the supraoccipital is deeper in specimens (No. 66136, from Chiricahua
Mts., and No. 204364, from Ash Creek in Graham Mts.) from mountains
geographically intermediate between the Huachuca Mountains and the White
Mountains. Also, the holotype of S. f. holzneri differs from S. n.
pinetis and agrees with other specimens of S. f. holzneri from
farther southwest in Arizona in the robustness of the posterior
extensions of the supraorbital processes and in the considerable degree
of fusion of the tips of these processes with the squamosals.
Additionally, the rostrum of the holotype is wide and deep as in other
specimens of S. floridanus from more eastern localities and is unlike
the narrow and shallow rostrum of S. n. pinetis.
If intergradation occurs in Arizona between the species Sylvilagus
floridanus and Sylvilagus nuttallii, as Nelson (op. cit.:200)
intimated it might, the intergrades probably will be found along the
Tonto Rim or in the territory between the Blue Range and the Graham
Mountains.
Sylvilagus floridanus cognatus Nelson
1907. Sylvilagus cognatus Nelson, Proc. Biol. Soc. Washington,
20:82, July 22.
We have examined the specimens recorded by Nelson (N. Amer. Fauna,
29:193, August 31, 1909) and conclude that Nelson (op. cit.)
accurately described them. We differ from Nelson on one point of
interpretation; we prefer to use the trinomial, instead of the binomial,
for cognatus because the kind and amount of difference between it and
subspecies of Sylvilagus floridanus (S. f. holzneri and possibly S.
f. llanensis) is on the order of magnitude that distinguishes
subspecies, and not full species, of Sylvilagus.
The specimen (W.D. Hollister, original No. 208) from the Datil
Mountains, lent to us by the Colorado Museum of Natural History, does
have, as Nelson (op. cit.) pointed out, larger tympanic bullae and a
slenderer rostrum than do other specimens of S. f. cognatus.
Nevertheless, No. 208, agrees with cognatus and differs from
Sylvilagus nuttallii pinetis in the greater vertical depth of the
zygoma, the greater transverse width of the first pair of upper
incisors, the broader posterior extensions of the supraorbital
processes, the fusion (instead of freedom from, or mere touching to, the
braincase) of the tips of these extensions, the less upturned
supraorbital processes, and the more nearly truncate posterior margin of
the supraorbital shield. Therefore, the specimen is referable to
Sylvilagus floridanus cognatus. The slender rostrum and large tympanic
bullae of No. 208 are either individual variations or features peculiar
to the population of Sylvilagus floridanus in the Datil Mountains.
Sylvilagus floridanus robustus Bailey
1905. Lepus pinetis robustus V. Bailey, N. Amer. Fauna, 25:159,
October 24.
Nelson (N. Amer. Fauna, 29:194–195, August 31, 1909) described specimens
from the Big Bend area of Texas. This was the only area from which
Nelson had specimens. Our examination of these same specimens indicates
that his description of them was accurate. Davis and Robertson (Jour.
Mamm., 25:271, September 8, 1944) recorded a specimen, under the name
Sylvilagus robustus, from "The Bowl, Guadalupe Mountains, Culberson
County, Texas." Our examination of the skull of this specimen
(♀ adult, No. 658, Mus. Zool., Louisiana State
University) indicates that it is, among named kinds of rabbits, best
referred to robustus. The specimen is morphologically as well as
geographically intermediate between S. f. cognatus and S. robustus.
This morphological intermediacy is illustrated by certain of the
following cranial measurements of three adult females: No. 108695
(robustus), Chisos Mts.; No. 658 from the Guadalupe Mts.; and No.
128651, NE slope Capitan Mts. Basilar length, 59.2, 54.2, 54.4; length
of nasals, 33.9, 31.1, 32.2; breadth of rostrum above premolars, 19.3,
17.5, 17.0; depth of rostrum in front of premolars, 15.8, 14.8, 14.0;
interorbital breadth, 20.4, 19.1, 19.7; parietal breadth, 27.2, 27.1,
26.5; diameter of bulla, 13.3, 12.2, 10.7. Considering the intermediate
nature of specimen No. 648, and the kind and amount of difference
between Sylvilagus floridanus cognatus and S. robustus, it seems
appropriate to us to use the name-combination Sylvilagus floridanus
robustus.
Actual intergradation, in the sense of interbreeding between individuals
of a continuously distributed population of animals, probably does not
occur regularly between S. f. cognatus and S. f. robustus nor
between several populations within either one of these subspecies; in
south-central Arizona and western Texas the animals are said to occur
only in the higher parts of the mountains. Consequently a given
population is separated from another by low-lying territory inhospitable
to the species Sylvilagus floridanus. This low-lying territory is
inhabited by another species, Sylvilagus audubonii. More intensive
collecting in the region concerned may, however, show a continuous
distribution of the species Sylvilagus floridanus in several areas
where it seems now to have an interrupted distribution.
Sylvilagus audubonii neomexicanus Nelson
1907. Sylvilagus audubonii neomexicanus Nelson, Proc. Biol. Soc.
Washington, 20:83, July 22.
Nelson (N. Amer. Fauna, 29:230, August 31, 1909) listed under
Sylvilagus audubonii cedrophilus Nelson an adult female, skin with
skull (U.S. Nat. Mus., Biol. Surv. Coll., No. 108698) from fifteen miles
south of Alpine, Texas. Nelson (loc. cit.) remarked that the
"bleached" color of the back and the great lateral breadth of the
tympanic bullae of No. 108698 were peculiarities not possessed by any
other specimen examined. Geographically, the locality of capture is far
south of other known occurrences of S. a. cedrophilus and
approximately on the boundary separating the range of S. a. minor from
that of S. a. neomexicanus. The large size, which may have induced
Nelson to refer the specimen to S. a. cedrophilus, is not surprising
considering that the individual is a female and fully adult. A
combination of new and old fur on the upper parts presents a pattern
that might be duplicated in other specimens of S. a. neomexicanus. The
lateral inflation of the tympanic bullae can be interpreted as
intergradation with the geographically adjacent S. a. minor to the
south; S. a. minor has large bullae. There are no features otherwise
which suggest that the specimen is anything other than Sylvilagus
audubonii neomexicanus and we refer it to that subspecies.
Sylvilagus audubonii minor Mearns
1896. Lepus arizonae minor Mearns, Proc. U.S. Nat. Mus., 18:557,
June 24.
1907. S[ylvilagus]. a[uduboni]. minor, Nelson, Proc. Biol. Soc.
Washington, 20:83, July 22.
Nelson (N. Amer. Fauna, 29:230, August 31, 1909) listed, without
comment, under Sylvilagus audubonii cedrophilus Nelson, a skin with
skull inside (Amer. Mus. Nat. Hist., 5419, ♀ adult or sub-adult) from San Diego,
Chihuahua, Mexico. We locate San Diego approximately 230 miles south and
60 miles east of El Paso, Texas. Thus, the specimen is from near the
center of the geographic range of Sylvilagus audubonii minor. With the
permission of Mr. G.G. Goodwin of the American Museum of Natural History
we removed the skull. It differs in no essential features from those of
other specimens of S. a. minor. For example, of specimens in the
United States National Museum, Biological Surveys Collection, a female
(No. 132002) from Guzman in Chihuahua, and a male (No. 51020) from Santa
Rosalia in the same state, are almost indistinguishable from the San
Diegan specimen. The specimen is without external measurements but the
length of the hind foot and length of ear from the notch in the dry
state (80 and 57, respectively) agree with the corresponding
measurements of S. a. minor. Color of the skin furnishes no diagnostic
character as between S. a. minor and S. a. cedrophilus. We identify
the specimen from San Diego as Sylvilagus audubonii minor.
Transmitted January 30, 1951.
24–7436