(DRAFT) - Taxonomy
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
TAXONOMY
NAME - SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
OTHER COMMON NAMES - SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN; SNAKE, RATTLE+, RIDGENOSE, NEW MEXICO; SNAKE, RATTLE+, RIDGE-NOSE; SNAKE, RATTLE+, RIDGENOSED and CHIHUAHUA; CASCABEL
ELEMENT CODE -
CATEGORY - Reptiles
PHYLUM AND SUBPHYLUM - CHORDATA,
CLASS AND SUBCLASS - REPTILIA,
ORDER AND SUBORDER - SQUAMATA,
FAMILY AND SUBFAMILY - VIPERIDAE,
GENUS AND SUBGENUS - CROTALUS,
SPECIES AND SSP - WILLARDI, OBSCURUS
SCIENTIFIC NAME - CROTALUS WILLARDI OBSCURUS
AUTHORITY -
TAXONOMY REFERENCES -
COMMENTS ON TAXONOMY -
New Mexican Ridge-nosed Rattlesnake
Crotalus willardi obscurus Harris and Simmons, 1976
KINGDOM: Animal GROUP: Reptile
PHYLUM: Chordata CLASS: Reptilia
ORDER: Squamata FAMILY: Viperidae
Ridgenose rattlesnakes (Crotalus willardi Meek, 1903) differ from
other members of their genus in having upturned internasal and canthal
scales that form a ridge around the front of the snout (31).
Individuals of the species are relatively small, attaining a length of
about 2 feet (600 cm) (20). The dorsal coloration consists of a light
brownish background overlain with pale crossbands with dark edges.
The underparts are whitish to pale brownish. The New Mexican
ridgenose rattlesnake, Crotalus willardi obscurus (Harris and Simmons,
1976), has grayish-tan underparts, versus more reddish brown hues in
the other races of the species. C.w. obscurus is further
distinguished from the other subspecies by the lack or obscurity of
whitish facial markings. Specifically, there is no white vertical
line on the rostal or mental (as on C.w. willardi, C.w. amabilis, and
C.w. meridionalis) and generally no white flashmark on the sides of
on the head (as C.w. silus) , although some specimens from the
Taxonomy - 1 (DRAFT) - Taxonomy
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
Sierra San Luis have a flashmark present (11,12).
The ridge-nosed rattlesnake (Crotalus willardi), as a species,
occurs in southeastern Arizona, southwestern New Mexico, and the
Mexican States of Sonora, Chihuahua, Durango, and Zacatecas (11).
Five subspecies have been described, with the nominate subspecies
found in the Huachuca, Santa Rita, and Patagonia Mountains of Arizona
(09,10,11,38) and in the Sierra de Cananea of Sonora (07,09,11). The
subspecies C.w. silus has the largest distribution: "the Sierra
Madre Occidental of western Chihuahua and eastern Sonora along the
Continental Divide and including the Sierra Huachinera, Sierra del
Tigre, Sierra de Oposura, Sierra Nacozari, Sierra Aconchi and from
near Yecora" (07). It is also found in the Sierra Los Ajos, and
the Sierra la Purica. C.w. merdidionalis is found in the Sierra Madre
Occidental of southern Durango and northern Zacatecas (05). The
remaining two subspecies have very limited distribution: C.w.
amabilis is known only from the Sierra del Nido in Chihuahua (01); and
C.w. obscurus occurs in the Animas and possibly Peloncilla Mountains
of New Mexico (03,07) and in the Sierra San Luis of Mexico (07,12).
The ridgenose rattlesnake is named in honor of Frank C. Willard,
who collected the type specimen in southeastern Arizona (28). Klauber
then described two races of the species from Mexico, i.e., C.w. silus
from Chihuahua and C.w. merdidionalis from Durango (19). Anderson
later described a fourth subspecies, C.w. amabilis, from the isolated
Sierra del Nido of central Chihuahua (01). Harris (1974) (09) and
Harris and Simmons (1976) (12) assigned the name C.w. obscurus to both
the ridgenose rattlesnake of the Animas Mountains of NM and the San
Luis Mountains of Chihuahua (12). Formerly these two populations were
considered to be of the race C.w. silus (05,18,20). C.w. obscurus has
been accepted as a valid race by the Society for the Study of
Amphibians and Reptiles, the USFWS, and the NM Department of Game and
Fish (04,06,15,26,33) pending further taxonomic study. Common names
used for the New Mexican ridge-nosed rattlesnake include: New Mexico
ridgenose rattlesnake, ridge-nose rattlesnake, Chihuahua ridgenosed
rattlesnake, and in Mexico, the "cascabel."
The type specimen of C.w. willardi is at the Field Museum of
Natural History in Chicago, IL, while that of C.w. obscurus is at the
U.S. National Museum of Natural History in Washington, DC. Additonal
museum specimens of the latter form exist at the University of New
Mexico, the American Museum of Natural History, the Los Angeles County
Museum of Natural History, the University of Arizona, the Univ. of
Texas at Arlington, and the Natural History Society of Maryland
collection (04). Captive specimens are present in various zoos and
private collections, and several photographic records of the race
are also in existence (12,13,25,34).
Taxonomy - 2 (DRAFT) - Status
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
STATUS
Coded Status
T: Federal Threatened
Commercial
Game (Consumptive Recreational)
COMMENTS ON STATUS -
U.S. STATUSES AND LAWS:
The New Mexican ridge-nosed rattlesnake (Crotalus willardi
obscurus) has been designated a Threatened species pursuant to the
Endangered Species Act of 1973 (50 CFR 17.11; P.L. 93-205, 87 Stat.
884; 16 U.S.C. 1531-1540), as amended. The subspecies has this status
wherever found including Mexico and the State of New Mexico. Critical
Habitat is designated for this species in Hildalgo County, NM at
elevations between 6,200 feet and 8,532 feet in Bear, Indian, and
Spring Canyons in the Animas Mountains (50 CFR 17.95(c)).
This subspecies is protected by the Lacey Act (P.L. 97-79, as
amended; 16 U.S.C. 3371 et seq.) which makes it unlawful to import,
export, transport, sell, receive, acquire, or purchase any wild
animal (alive or dead including parts, products, eggs, or offspring):
(1) in interstate or foreign commerce if taken, possessed,
transported or sold in violation of any State law or
regulation; or
(2) if taken or possessed in violation of any U.S. law,
treaty, or regulation or in violation of Indian tribal law.
It is also unlawful to possess any wild animal (alive or dead
including parts, products, eggs, and offspring) within the U.S.
territorial or special maritime jurisdiction (as defined in
18 U.S.C. 7) that is taken, possessed, transported, or sold in
violation of any State law or regulation, foreign law, or Indian
tribal law.
RESPONSIBLE FEDERAL AGENCIES:
USFWS -Responsible for the management/recovery, listing, and
law enforcement/protection of this species.
All Federal agencies have responsibility to ensure that any
action authorized, funded, or carried out by that agency is not likely
to jeopardize the continued existence of the species or result in the
destruction or adverse modification of Critical Habitat (50 CFR 402),
and to utilize their authorities to carry out programs for the
conservation of the species.
STATE STATUSES AND LAWS:
Status - 1 (DRAFT) - Status
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
STATE: New Mexico
DESIGNATED STATUS: Endangered Group I
ADMINISTRATIVE AGENCY: New Mexico Department of Game and Fish
STATE STATUTE: Regulation No. 624, March 28, 1985. New Mexico
Statutes Annotated 17-2-37 to 17-2-46.
INTERNATIONAL STATUSES, TREATIES, AND AGREEMENTS:
This species (Crotalus willardi) is listed as Endangered in
Mexico's "Especies de Fauna en Peligro de Extincion en Mexico";
a recommendation to CITES (Reyes; August 1982).
ECONOMIC STATUSES:
This species has value as a component of New Mexico's natural
heritage of biotic diversity. Collection and some commercial
exploitation of this particular rattlesnake has happened in the past
and may still continue.
77/05/26:42 FR 27007/27009 - Proposed Threatened w/ Critical Habitat
78/07/04:43 FR 34476/34480 - Listed as Threatened w/ Critical Habitat
83/12/08:48 FR 55100/55102 - Five year review
85/07/22:50 FR 29900/29901 - Five year review
Status - 2 HABITAT ASSOCIATIONS
HABITAT - TERRESTRIAL
TERRESTRIAL
SOCIETY OF AMERICAN FORESTRY TYPES
SAF TYPE STAGE CLOSURE
Shortleaf Pine-Oak shrub--seedling
Shortleaf Pine-Oak young tree
Shortleaf Pine-Oak mature tree
Shortleaf Pine-Oak Old Growth
Douglas-fir-western hemlock shrub--seedling
Douglas-fir-western hemlock young tree
Douglas-fir-western hemlock mature tree
Douglas-fir-western hemlock Old Growth
LAND USE -
Deciduous Forest Land
Evergreen Forest Land
Mixed Forest Land
Shrub and Brush Rangeland
Mixed Rangeland
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Palustrine SS6
COMMENTS ON HABITAT ASSOCIATIONS -
Although explored biologically as early as 1892 (27), detailed
descriptions of habitats of C.w. obscurus date mainly from recent
years. In particular, the habitats in the Animas Mountains of NM
have been surveyed botanically (36) and classified in detail (14) only
in the last decade. The San Luis Mountains of Mexico have yet to be
so treated, although more fragmentary information exists from them
(10,21,27). In general, the floras of the two ranges are similar,
with a predominance of evergreen forests at higher elevations. The
San Luis Mountains are somewhat more mesic than are the Animas, with
the additions of such species as Arizona cypress (Cupressus
arizonica), bigtooth maple (Acer grandidentata), and other riparian
plants. To what extent this increased mesicness may benefit C.w.
obscurus in the San Luis Mountains is unknown.
In the Animas Mountains, C.w. obscurus has been found in and
adjacent to habitats classified as Douglas fir forest, pine-oak
woodland, Emory oak woodland, Arizona oak woodland, netleaf/
silverleaf oak woodland, Gambel oak woodland, riparian woodland,
pinyon-juniper woodland, manzanita chaparral, oak chaparral, mixed
chaparral, and talus slopes (14). However, of these the most
frequently occupied by the snake, in the Animas, are the following:
Pine-oak woodland: Dominated by Chihuahua and Apache pines (Pinus
leiophlla and P. engelmannii), with an understory of netleaf,
silverleaf, Arizona and Gambel oaks (Quercus rugosa, Q. hypoleucoides,
Q. arizonica, and Q. gambelii), alligator juniper (Juniperus
deppeana), Mexican pinyon (Pinus cembroides), shrubs, forbs, and
grasses. This habitat occurs on perhaps 200 acres from 5600 to 8000
feet in elevation, typically in canyons.
Habitat Associations - 1 Arizona oak woodland: Dominated by Arizona oak; occupies several
hundred acres from 5600 to 6500 feet in elevation, mainly in canyon
bottoms.
Netleaf/silverleaf oak woodland: Dominated by netleaf and silverleaf
oaks; occurs on several hundred acres at 6000 to 8000 feet in
elevation, including canyon bottoms.
Gambel oak woodland: Dominated by Gambel oak; occurs on a few hundred
acres at 7000 to 8000 feet in elevation, typically in canyon bottoms.
Riparian woodland: Dominated by various broadleaf trees and shrubs
and is typically associated with one or more of the above habitats,
generally in canyons or drainages (National Wetland Inventory type
P0SS6).
Manzanita chaparral: Dominated by manzanita (Arctostaphylos pungens);
occurs on several hundered acres at 7000 to 8500 feet in elevation,
typically on slopes.
Oak chaparral: Dominated by shrubby netleaf and silverleaf oaks, with
an admixture of other shrubs, plus forbs and grasses. Occurs on
several thousand acres at 7000 to 8500 feet in elevation, typically on
slopes.
Of the above habitats, those that occur in and near canyon
bottoms appear to be the essential ones for C.w. obscurus. These are
typically dominated by pines, oaks, and associated trees, shrubs,
forbs, and grasses. In total this combination of elements occupies at
most a few thousand acres in the Animas Mountains, mainly at
elevations of 5600 to 8000 feet. The rattlesnake has been detected
over a similar altitudinal range, that being 6100 to 7700 feet in
elevation (02). C.w. obscurus occurs in similar habitats in the
San Luis Mountains.
Rocks, leaf litter, and mesic conditions commonly are mentioned
in C. willardi habitat descriptions. The annual percipitation in
the Animas Mountains is about 20 inches and the annual evaporation
is about 65 inches. The only known permanent water is Turkey (=Aspen)
Spring, which has very low flow in the upper portion on Indian Creek
Canyon. Winter retreats are probably talus areas and other
Labyrinthian formations (e.g., rock outcrops, cliffs/ledges, etc.)
which probably serve as thermal refugia that allow the snakes
to maintain body temperatures above some critical thermal minimum.
Concealment appears to be an important requirement of C. willardi
because snakes blend well into the background of preferred substrate
(e.g., leaf litter and downed logs) (05,12,26).
Habitat Associations - 2 (DRAFT) - Food Habits
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
FOOD HABITS
TROPHIC LEVEL -
CARNIVORE
LIFESTAGE FOOD FOOD PART
General Aves
General Mammalia
General Carrion
General Reptilia
Food Habits - 1 (DRAFT) - Environment Associations
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
ENVIRONMENTAL ASSOCIATIONS
G = General A = Adult
LIM = Limiting RA = Resting Adult
J = Juvenile FA = Feeding Adult
RJ = Resting Juvenile BA = Breeding Adult
FJ = Feeding Juvenile P = Pupae
L = Larvae E = Egg
RL = Resting Larvae
FL = Feeding Larvae
LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
G Aquatic Features: Springs [flowing]
G Terrestrial Features: Talus
G Terrestrial Features: Cliffs/ledges
G Terrestrial Features: Rock outcrops
G Terrestrial Features: Downed logs
Environment Associations - 1 (DRAFT) - Life History
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
LIFE HISTORY
FOOD HABITS:
The food habits of Crotalus willardi in the wild have not been
studied much. Presumably the bulk of the diet consists of small
vertebrates that the snake itself kills. Lizards may be the chief
prey, with lesser numbers of small mammals, birds, and even
invertebrates being taken on occasion (35). The most frequently
recorded prey species include the Yarrow's spiny lizard (Sceloporus
jarrovii) and the Arizona alligator lizard (Elgaria kingii) (19,37),
plus the brush mouse (Peromyscus boylii) (20,37). Other species
recorded as prey were the Wilson's warbler (Wilsonia pusilla) (20),
rufous-crowned sparrow (Aimophila ruficeps) (29), and once a scorpion
was disgorged (20). In captivity, C. willardi has been known to
prefer lizards to small rodents as prey (03). Suggestions that this
species might feed on carrion or employ facial or caudal luring to
capture prey (02) have limited supporting evidence.
Although hard data on the food habits of C. willardi are few,
several considerations provide additional insights into the subject.
The species is a small-bodied snake living in a periodically cool
environment. Thus, not only are its prey items limited to those of
small size, but C. willardi must also cope with the thermoregulatory
problems in being able to seek prey. Even in summer, when maximum
temperatures are reached in its montane environment, this species
faces cool periods at night, during cloudy weather, and as a result of
its microhabitat selection; e.g., canyon bottoms where solar gain is
less. To cope with these factors, one would expect C. willardi to be
more active by day than lowland rattlesnakes. Given that the most
available prey would be small rodents, lizards, and birds,
one would expect that C. willardi would be a rather active, even agile
species compared to lowland congeners. Evidence for such suppositions
is limited, but C. willardi is known to be rather active by day (02).
It shows a tendancy to climb or rest on vegetation (02,14). Yarrow's
spiny lizard, a principle food of this snake, maintains a nearly
season-long activity period by orienting itself on talus slopes
to direct sunlight. Therefore, these talus slopes provide thermal
conditions that allow for a nearly year-round food source for
C. willardi. Prey abundance at these sites may play a significant
role in the selection of talus slopes by C. willardi.
HOME RANGE/TERRITORY:
Rattlesnakes almost certainly have home ranges, but defining them
is difficult (20). As for C.w. obscurus, the only direct evidence
concerning territorial fidelity involves a distinctively marked
individual that was recaptured in the Animas Mountains on three
occasions in the period of July-October 1976 (14). On each occasion
the snake was within 18 inches of the original point of capture. This
is remarkable, especially considering the fact that the point of
capture was in a stand of grass rather than in a crevice or other
retreat. C. willardi hibernates in protected areas that
do not freeze, probably in small groups and possibly with other snake
species. Two C.w. obscurus found in rock talus in October may have
been near such a denning area, especially given that additional ones
Life History - 1 (DRAFT) - Life History
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
were found at the site in other years (02).
PERIODICITY:
C.w. obscurus, is known to be active as early as April (03) and
as late as October (02,14). An analysis of the records of the species
shows that most are from the months of July-September; however, these
may also be the months in which most collectors sought the species.
These months also coincide with the rainy season in the Animas
Mountains, and it is possible that the apparent increase in activity
by these snakes is correlated with the rains. For example, higher
humidity may ameliorate temperatures and provide more optimal
conditions under which these rattlesnakes might be active.
Daily activity patterns for C. willardi have been summarized
(02), but the data may be ambiguous. In particular, relatively
fixed diurnal cycles in conjunction with periods of rain or other
weather phenomena, have not been verified. However, given factors
such as the species size and environment, C. willardi is probably
active during periods of moderate temperatures, both diurnal, and
seasonally. Thus, during cool weather one would expect the
species to be active in the warmest part of the cycle, e.g., mid-day.
Conversely, it should be active during the morning and late afternoon-
early evening in warm weather. Currently, there are no records
of nocturnal activity in the species (02), although this snake is
probably active on warm nights.
MIGRATION PATTERNS:
Other than movements to and from winter refuges, no migration is
is known or suspected in C. willardi.
COVER/SHELTER REQUIREMENTS:
As with many other snakes, C. willardi requires cover and shelter
to escape from both bad weather and from predators, and these are
probably also essential elements in its seeking of prey, reproduction,
and other activities. Winter retreats are probably talus areas and
other labyrinthian formations (e.g., rock outcrops, cliffs/ledges,
etc.) that allow the snakes to move below the frost line. Similar
sites may be used at other times of the year, although in warm weather
C. willardi is often found on or near vegetated areas
(02). Such vegetation would provide numerous features needed by the
snakes, including shade, a more stable temperature regime, and
concealment. Concealment appears to be an important consideration in
the requirements of C. willardi, and it is probably no accident that
the snake blends well into the background, e.g., leaf litter and
downed logs (05,12,26). The species probably relies to a considerable
extent on concealment in obtaining prey, both from an immobile
position and while cruising. This concealment is probably also a key
feature in escaping predators of this specis, especially as long as a
snake remains immobile. Such immobility is well-practiced by C.w.
obscurus, to the extent that rattling seems to occur only as a
last resort. However, once disturbed the species may rattle and
attempt to crawl away, including into denser cover if available.
REPRODUCTIVE SITE REQUIREMENTS:
Life History - 2 (DRAFT) - Life History
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
Rattlesnakes are ovoviviparous, with fertilized eggs being
retained in the female until hatching occurs (20). Other than an
environment with protection against extremes of weather and predation,
no special requirements are known to be necessary for reproduction to
occur. Presumably prey must be available for the young soon after
they disperse, which is almost immediately after birth.
REPRODUCTIVE CHARACTERISTICS:
C. willardi is known to reach sexual maturity when 80 percent
full grown, which would be at a length of 450 mm or more (02,20).
Copulation has been reported only once from the wild, that involving a
pair of C.w. silus in Sonora in July (03). Copulation last from 6 to
12 hours in rattlesnakes (20), but bouts of up to 24 hours have been
observed in captive C. willardi (32). Sexual activity may be induced
by the inception of summer rains and/or the shedding of the skin in
females (02,32); however, the subject is poorly researched, especially
in the wild.
Given that the gestation period of C. willardi is 13 months, it
is likely that the species only reproduces biennially (32).
Paturition has been recorded mainly in August (03,22,32), with one
record for September (24). The average number of young in 12 broods
of five subspecies of C. willardi was 5.5, with the the range from 2
to 9 (02). By comparison, larger species of rattlesnakes have more
young per brood; typically in the range of 10 to 20 (20). The average
weight in newborn C. willardi is 6.29 grams, and the average length is
190.8 millimeters (02). The newborns resemble adults (25), except for
being browner and in having yellow-orange lip pigment (20,32).
C.w. obscurus neonates have a black tail-tip, not yellow as in
other species.
PARENTAL CARE:
Newborn rattlesnakes share a presence with their mothers only as
a result of the birth experience, and dispersal occurs within a day or
so of that event (20). So far as is known, the female in no way
assists the young after birth, although her proximity could well deter
predation on them.
POPULATION BIOLOGY:
Little is known of the age and sexual profiles of wild
populations of C. willardi, and density and population estimates are
lacking.
SPECIES INTERRELATIONSHIPS:
Very little is known about interrelationships between C. willardi
and other species in its environment. Those for which the most is
known involve species on which the rattlesnake might prey, but even
that information is spotty. For example, a correlation may exist
between the appearance of newborn C. willardi and the hatching of
certain lizards (e.g., Sceloporus jarrovi) as is stated to be the case
in two other rattlesnakes (i.e., C. lepidus and C. pricei) and that
lizard (17). However, more study is needed not only to establish the
existence of such an interrelationship, but also to determine the
extent to which the two species are affected.
Life History - 3 (DRAFT) - Life History
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
Other relationships that could be explored in C. willardi are
those involving predation. One would assume that mammals, birds, and
other snakes occasionally take C. willardi as prey, as they do with
other rattlesnakes (20). However, this factor in C. willardi remains
poorly known, to the extent that no predation on C. w. obscurus seems
to have been reported. Nontheless, several potential predators exist
in the range of the subspecies, including king snakes, carnivorous
mammals, hawks, and owls.
OTHER LIFE HISTORY DESCRIPTORS:
Infestations of the flagellates, Monocercomas and Pseudomonas and
the bacterium Salmonella arizonae, have been reported in captive C.
willardi (16), but how or if these infest wild populations, or have
any negative impact on them, is not known.
Life History - 4 (DRAFT) - Management Practices
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Beneficial Restricting/regulating human disturbance of populations
Beneficial Land Acquisition
Beneficial Stocking captive-reared wild-strain animals
Beneficial Restricting Poaching
Adverse Incidental Capturing/Killing
Existing Incidental Capturing/Killing
Adverse Collecting
Existing Collecting
Adverse Commercial Exploitation
Existing Commercial Exploitation
Adverse Low Gene Pool
Existing Low Gene Pool
Adverse Competition
Existing Competition
Adverse Grazing
Existing Grazing
Adverse Fire
Existing Fire
COMMENTS ON MANAGEMENT PRACTICES -
The New Mexican ridge-nosed rattlesnake is listed as a federally
threatened species because of its limited range, vulnerability, and
the past excesses of collecting. Collecting probably had a
significant impact on the the New Mexican ridge-nosed rattlesnake
population. After the species was documented in the Animas Mountains
in 1957 (05), collectors came from all parts of the country to obtain
specimens (02). One researcher visiting the Animas Mountains
encountered fifteen collectors from six states, all seeking specimens
of the C.w. obscurus (10). During the 1960's and early 1970's, the
collection of the New Mexican ridge-nosed rattlesnake probably
increased, as the taking of species in Mexico and Arizona became more
difficult. Collecting permits were required in Mexico, and Arizona
gave the species complete protection in January 1975 (07,10,11). In
1976 (12), the New Mexican ridge-nosed rattlesnake was recognized as a
distinct subspecies, adding to its value to collectors.
Unfortunately, collectors not only took rattlesnakes from the
Animas Mountains, but they also destroyed or altered habitat in their
collection efforts (07,10). Rock and log turning and the use of
crowbars or gasoline on rock outcroppings were employed as collecting
techniques, to the detriment of the snake's habitat (10,11).
Excessive grazing may have reduced habitat, further restricting the
distribution of this species.
Infestations of the flagellates Monocercomas and Pseudomonas and
the bacterium Salmonella arizonae have been reported in captive C.
willardi (16), but how or if these infest wild populations or have any
negative impact on them is not known. Although disease is not known
to limit wild populations of C.w. obscurus, the highly disjunct range
of this species makes it vulnerable to extinction due to disease and
Management Practices - 1 (DRAFT) - Management Practices
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
habitat loss. Recolonization after a major die-off would be virtually
impossible (04).
Future threats to the species:
The largest threat to the New Mexican ridge-nosed rattlesnake is
loss of habitat in the Animas and San Luis Mountains. Loss of habitat
could occur as a result of several reasons such as grazing,
development, off-road vehicle use, pollution, mining, timber
harvesting, or other factors.
APPROVED PLAN:
U.S. Fish and Wildlife Service. 1985. New Mexico Ridge-nosed
Rattlesnake Recovery Plan. U.S. Fish and Wildlife Service,
Albuquerque, NM. 59 pp.
The primary objective of the Recovery Plan is to maintain and
enhance the status of the New Mexico ridge-nosed rattlesnake to the
point that survival of the Animas Mountains and Sierra San Luis
populations is assured. Of primary importance is the protection of
the snake and its habitat through enforcement of the Endangered
Species Act of 1973, and the New Mexico Wildlife Conservation Act of
1974 to prevent poaching, harrassing, killing, or habitat destruction.
Efforts should be directed at ensuring the long term protection
of Critical or essential habitat in the U.S. by establishing new
cooperative agreements with current landowners and/or renewing the
management plan prepared under the cooperative agreement with the
previous owners. In the event a new cooperative agreement cannot be
signed, other alternatives (easements, lease or other legal
agreements to aquire management rights) should be sought. Development
of a joint U.S./Mexico agreement to protect individuals and
populations and to study the species in Mexico is also recommended.
Since little is known about ridge-nosed rattlesnakes in general
and this subspecies in particular, studies should be initiated that
should include:
1) Monitoring species populations (numbers, condition, and age
structure), and may include radio tagging of captured individuals for
detailed study.
2) Determination of habitat requirements, including vegetation
and associated parameters.
3) Behavior patterns (activity and reproduction).
4) Prey relationships and the availability of potential prey.
5) Sources of mortality (predation, disease, man's impacts
(restricted access to areas in the Animas Mountains has already
minimized effects), and related factors).
Based on these studies and other information, steps to reduce or
eliminate threats to survival of the species should be developed and
implemented. The taxonomic status of Crotalus willardi populations
throughout their range should be studied, particularly the
relationship between the Animas Mountains population and the San Luis
Mountains population in Chihuahua. Two or three captive
populations of New Mexico ridge-nosed rattlesnakes should be
established for scientific research. Surplus individuals could be
Management Practices - 2 (DRAFT) - Management Practices
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
released into both the Animas Mountains and the Sierra San Luis to
augment existing populations should the need arise. Finally, public
awareness of the uniqueness of the New Mexico Ridge-nosed Rattlesnake
should be increased through the use of the local, State and National
broadcasts and print media.
In 1974 a cooperative agreement was signed with a private company
restricting access to unauthorized entry to rattlesnake habitats in
the Animas Mountains. Since these lands were sold in 1982 to another
company, the agreement has not been renewed although the management
plan remains in effect. The Service is presently negotiating to
acquire the Animas Mountains.
Management Practices - 3 (DRAFT) - References
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
References
***** REFERENCES FOR ALL NARRATIVES EXCEPT N-OCCURRENCE *****
01 Anderson, J.D. 1962. A new subspecies of the ridge-nosed
rattlesnake, Crotalus willardi, from Chiuahua, Mexico. Copeia,
1962(1):160-163.
02 Applegarth, J.S., J.C. Bednarz and M.A. Williamson. 1980. The
ridge-nosed rattlesnake in New Mexico: A review of existing
information and a search for suitable habitat on public lands.
Unpubl. Rept. to the BLM, Las Cruces, NM.
03 Armstrong, B.L. and J.B. Murphy. 1979. The natural history of
Mexican rattlesnakes. Univ. Kansas Mus. Nat. Hist., Special Publ.
No. 5. 88 pp.
04 U.S. Fish and Wildlife Service. 1985. New Mexico Ridge-nosed
Rattlesnake Recovery Plan. U.S. Fish and Wildlife Service,
Albuquerque, NM. 59 pp.
05 Bogert, C.M. and W.G. Degenhardt. 1961. An addition to the fauna
of the United States, the Chihuahua ridge-nosed rattlesnake in New
Mexico. Amer. Mus. Noviates, 2064:15 pp.
06 Collins, J.T., R. Conant, J.E. Huheey, J.L. Knight, E.M. Rundquist
and H.M. Smith. 1982. Standard common and scientific names for
North American amphibians and reptiles. Soc. for the Study of
Amphibians and Reptiles. Circular 12:1-28.
07 Degenhardt, W.G. 1972. The ridge-nosed rattlesnake: An Endangered
species. Pages 104-113 In: Symposium on rare and Endangered
wildlife of the southwestern United States. NM Dept. of Game and
Fish, Santa Fe. 167 pp.
08 Degenhardt, W.G. 1975. The first year of study of the Animas
ridge-nosed rattlesnake, Crotalus willardi. Unpublished Report on
file at: U.S. Fish and Wildlife Service, Albuquerque, NM. 4 pp.
09 Fitch, H.S. 1970. Reproductive cycles in lizards and snakes.
Univ. of Kansas, Mus. Nat. Hist. 8:213-274.
10 Harris, H.S., Jr. 1974. The New Mexican ridge-nosed rattlesnake.
National Parks and Conservation 48:22-24.
11 Harris, H.G., Jr. and R.S. Simmons. 1975. An Endangered species,
the New Mexican ridge-nosed rattlesnake. Bull. MD Herp. Soc.
11(1):1-7.
12 Harris, H.G., Jr. and R.S. Simmons. 1976. The paleogeography and
evolution of Crotalus willardi, with a formal description of a new
subspecies from New Mexico, United States. Bull. MD Herp. Soc.
12(1):1-22.
13 Harris, H.G., Jr. and R.S. Simmons. 1978. A preliminary account
of the rattlesnakes with the descriptions of four new subspecies.
Bull. MD Herp. Soc. 14:105-211.
14 Hubbard, J.P. 1977. A biological inventory of the Animas
Mountains, Hidalgo County, New Mexico. Rept. distributed by the
Endangered Species Program, NM Dept. Game and Fish. 56 pp.
15 Hubbard, J.P., M.C. Conway, H. Campbell, G. Schmitt and M.D. Hatch.
1979. Handbook of species Endangered in New Mexico. NM Dept. Game
and Fish, Santa Fe. 215 pp.
16 Johnson, T.B. 1983. Status report on Crotalus willardi willardi.
USFWS, Albuquerque, NM. 70 pp.
References - 1 (DRAFT) - References
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
17 Kauffeld, C.F. 1943. Growth and feeding of newborn Price's and
green rock rattlesnakes. Amer. Midland Nat. 29:607-614.
18 Kauffeld, C.F. 1969. Snakes: The keeper and the kept. Doubleday
and Co., Inc., Garden City, NY. 248 pp.
19 Klauber, L.M. 1949. The subspecies of the ridge-nosed
rattlesnake, Crotalus willardi. Trans. San Diego Soc. Nat. Hist.
11(8):121-140.
20 Klauber, L.M. 1972. Rattlesnakes: Their habits, life histories,
and influence on mankind, 2nd ed. Univ. CA Press., Berkeley.
2 vol., 1533 pp.
21 Marshall, J.T., Jr. 1957. Birds of pine-oak woodland in southern
Arizona and adjacent Mexico. Cooper Orin. Soc., Pacific Coast
Avifauna No. 32. 125 pp.
22 Martin, B.E. 1975. Notes on a brood of the Arizona ridge-nosed
rattlesnake, Crotalus willardi willardi. Bull. MD Herp. Soc.
11:64-65.
23 Martin, B.E. 1975. An occurrence of the Arizona ridge-nosed
rattlesnake, Crotalus willardi willardi, observed feeding in
nature. Bull. MD Herp. Soc. 11:66-67.
24 Martin, B.E. 1975. A brood of the Arizona ridge-nosed
rattlesnakes (Crotalus willardi willardi) bred and born in
captivity. Bull. MD Herp. Soc. 11:187-189.
25 Martin, B.E. 1976. A reproductive record for the New Mexican
ridge-nosed rattlesnake (Crotalus willardi obscurus). Bull. MD
Herp. Soc. 12:126-128.
26 McCranie, J.R. and L.D. Wilson. 1978. A second Mexican specimen
of Crotalus willardi obscurus from the Sierra San Luis, Chihuahua,
with comments on other members of the herpetofauna. Herp. Rev.
9(3):108-109.
27 Mearns, E.A. 1896. Mammals of the Mexican boundry of the United
States. Pt. 1. Bull. U.S. Mus. 56.
28 Meek, S.E. 1905. An annotated list of a collection of reptiles
from southern California and northern lower California. Field
Columbian Mus., Zool. Ser. (Fieldiana:Zoology) 7:1-19.
29 Parker, S.A. and D. Stotz. 1977. An observation on the foraging
behavior of the Arizona ridge-nosed rattlesnakes, Crotalus willardi
willardi (Serpentes:Crotalidae). Bull. MD Herp. Soc. 13:123.
30 Russell, F.E. 1980. Snake venom poisoning. J.B. Lippincott Co.,
Philadelphia, PA. 562 pp.
31 Stebbins, R.C. 1966. A field guide to western reptiles and
amphibians: Field marks on all species in western North America.
Houghton Mifflin Co., Boston, MA. 279 pp.
32 Tryon, B.W. 1978. Reproduction in a pair of captive Arizona
ridge-nosed rattlesnakes, Crotalus willardi willardi (Reptilia,
Serpentes, Crotalidae). Bull. MD Herp. Soc. 14:83-88.
33 U.S. Fish and Wildlife Service. 1977. Proposed Endangered status
and Critical Habitat for the New Mexican ridge-nosed rattlesnake.
Federal Register 42:27007-27009.
34 U.S. Fish and Wildlife Service. 1980. In jeopardy - America's
Endangered species: Ridge-nosed rattlesnake. Leaflet. 4 pp.
35 Vorhies, C.T. 1948. Food items of rattlesnakes. Copeia
1948:302-303.
36 Wagner, W.L. 1977. Floristic affinities of the Animas Mountains,
References - 2 (DRAFT) - References
Species SNAKE, RATTLE+, RIDGE-NOSED, NEW MEXICAN
Species Id ESIS152006
Date 14 MAR 96
southwestern New Mexico. M.S. Thesis. Univ. NM. 180 pp.
37 Woodin, W.H. 1953. Notes on some reptiles from the Huachuca area
of southeastern Arizona. Bull. Chicago Acad. Sci. 9:285-296.
38 Fowlie, J.A. 1965. The snakes of Arizona. Azul Quinta
Press. Fallbrook, CA. iv + 164 pp.
***** REFERENCES FOR N-OCCURRENCE NARRATIVE ONLY *****
01 Anderson, J.D. 1962. A new subspecies of the ridge-nosed
rattlesnake, Crotalus willardi, from Chiuahua, Mexico. Copeia
1962(1):160-163.
02 Applegarth, J.S., J.C. Bednarz and M.A. Williamson. 1980. The
ridge-nosed rattlesnake in New Mexico: A review of existing
information and a search for suitable habitat on public lands.
Unpubl. Rept. to the BLM, Las Cruces, NM.
03 Bogert, C.M. and W.G. Degenhardt. 1961. An addition to the fauna
of the United States, the Chihuahua ridge-nosed rattlesnake in New
Mexico. Amer. Mus. Noviates 2064:15 pp.
04 Degenhardt, W.G. 1975. The first year of study of the Animas
ridge-nosed rattlesnake, Crotalus willardi. Unpublished report on
file at: U.S. Fish and Wildlife Service, Albuquerque, NM. 4 pp.
05 Harris, H.S., Jr. 1974. The New Mexican ridge-nosed rattlesnake.
National Parks and Conservation 48:22-24.
06 Harris, H.G., Jr. and R.S. Simmons. 1975. An Endangered species,
the New Mexican ridge-nosed rattlesnake. Bull. MD Herp. Soc.
11(1):1-7.
07 Harris, H.G., Jr. and R.S. Simmons. 1976. The paleogeography and
evolution of Crotalus willardi, with a formal description of a new
subspecies from New Mexico, United States. Bull. MD Herp. Soc.
12(1):1-22.
08 Hubbard, J.P. 1977. A biological inventory of the Animas
Mountains, Hidalgo County, New Mexico. Rept. distributed by the
Endangered Species Program, NM Dept. Game and Fish. 56 pp.
09 Johnson, T.B. 1983. Status report on Crotalus willardi willardi.
USFWS, Albuquerque, NM. 70 pp.
10 Klauber, L.M. 1949. The subspecies of the ridge-nosed
rattlesnake, Crotalus willardi. Trans. San Diego Soc. Nat. Hist.
11(8):121-140.
11 Klauber, L.M. 1956. Rattlesnakes: Their habits, life histories,
and influence on mankind. Univ. CA Press., Berkeley. 1476 pp.
12 McCranie, J.R. and L.D. Wilson. 1978. A second Mexican specimen
of Crotalus willardi obscurus from the Sierra San Luis, Chihuahua,
with comments on other members of the herpetofauna. Herp. Rev.
9(3):108-109.
References - 3