An Introduction to the Mexican Wolf and Conservation Status Briefing.

Species Report:

Mexican Wolf (Canis lupus baileyi)

Name of species

Mexican Gray Wolf (Canis lupus baileyi)

Classification:

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Class: Mammalia

Subclass: Eutheria (placental mammals)

Order: Carnivora

Family: Canidae

Genus: Canis

Physical Description:

The wolves of the Southwest are the smallest in size, most genetically unique, most endangered, and the southernmost subspecies of all North American gray wolves. There is a contentious debate about how many subspecies of gray wolves inhabited the Southwest historically, and that will perhaps be the topic of another article in the future. With recent advances in paleogenetic technology, the science on this will undoubtedly need to be revisited, but the literature I consulted at the time of writing this article back in 2017, one could ascertain that Zoologist Edward Alphonso Goldman along with Edward William Nelson, recognized up to five different sub-species of gray wolves in the Southwest.

-Canis lupus mogollensis (Goldman 1937). Arizona wolf of Mogollon and sub- Mogollon Arizona and west-central New Mexico.

-Canis lupus monstrabilis (Goldman 1937). The Texas wolf of the southwest and southeast New Mexico.

-Canis lupus nubilus (Thomas Say 1823) plains or buffalo wolf of the plains grasslands. Extended from Saskatchewan, Canada, through Oklahoma and Texas panhandles to northeast New Mexico and the Llano Estacado of New Mexico and Texas.

-Canis lupus youngi (Goldman 1937). Intermountain of the Great Basin, inhabiting Utah, southern Wyoming, eastern Colorado down to Arizona and northern New Mexico.

-Canis lupus baileyi (Nelson and Goldman 1929) Mexican wolf or Lobo found in Madrean montane forest evergreen woodlands and adjacent grasslands in Mexico, Arizona, and southwest New Mexico.

Of all the subspecies mentioned above, all are extinct today except Canis lupus baileyi.

Their general appearance, as described by Brown, is that of an oversized coyote, with a large head and a shorter muzzle and larger nose pad than coyotes (Canis latrans). Their color varies with the season as well as the individual, but can generally be described as richly colored buff, gray, rust, and black (Bass, 1998). Mexican wolves often display black in the tips of their ears and tails.

Adults range in length from 4 ½ to 5 ½ ft. (including their tail) and heights between 26 to 32 inches tall at the shoulder. Mexican Gray Wolf ranges between 50-90 lbs. in weight, and, just like their northern cousins, are sexually dimorphic, with males being taller and heavier than females. As with many canids, the sense of smell of wolves is acute and used for finding food sources, dense, and communication with members from their pack as well as rival wolves.

Identifying wolves in the wild by their tracks can sometimes be a challenging task. However, most times their tracks are easily distinguished from coyote tracks because they are larger and longer in size. Wolf tracks are usually bigger than 3 ½ inches and usually around 4 ½ (front paws) whereas coyotes and most domestic dogs (with the exceptions of a few breeds like Great Danes and St. Bernard’s that will imprint at around 4 inches ) will typically imprint at 3 ½ inches and below. Additionally, another notable difference is that the wolf’s track has its toes pointing straight forward whereas the dog’s outer digits will splay slightly outwards from the heel pad. Lastly, a wolf heel pad is larger than a dog of similar size

Wolves, as do most canines in general, consider the economy of energy when moving and use transit roads, washes, and other easy routes. Wolves employ a particular trot in which they sort of flail their forelegs in a very graceful rhythm. Wolves are digitigrade, meaning that they walk on their toes rather than the entire surface of their soles as opposed to other species that walk flat on their feet (plantigrades) such as bears, elephants, and yes, humans.

Habitat:           

Mexican wolves are found in a variety of habitats, preferring mountain oak woodlands or juniper and piñon forests and adjacent grasslands above 4,500 feet of altitude. There is conflicting information on whether they are low desert dwellers or not.

Unfortunately, because of the onslaught launched against wolves in the United States in the late 1800s and early 1900s, a lot of the behavior observed in wolves come from hunters and Wolfers (a term commonly used for civilian and government agency wolf hunters during the extermination of wolves in the continental U.S). Some of these behaviors observed can be considered atypical of the behavior observed in other subspecies of gray wolf. Author Rick Bass in his book “The New Wolves” (1998) describes is as follows: “It seems to me safe to say that the behavior of a persecuted species, in the final days before its extinction from the wild, may not represent how that species would prefer to behave in the wild under more “normal” conditions”.

Geographic Range:

Historically Mexican gray wolf roamed Texas, Arizona, New Mexico (per Brown, New Mexico was the only state where all five subspecies inhabited), southern Colorado, and the Mexican states of Sonora, Chihuahua, parts of Sinaloa, Durango, and Zacatecas. However, as of today, and after two decades of reintroduction of Mexican wolves back in the wild, they are restrained to the Mexican Wolf Recovery Area, a designed geographic area that includes Arizona and New Mexico down from Interstate 40 to the international border with Mexico and some parts of Mexico.

Social structure, hunting method, and natural prey:

Wolves form highly structured hierarchical groups, sometimes referred to as packs. According to the U.S. Fish and Wildlife Service, a typical Mexican wolf can consist of 4-8 members. These group sizes can change by dispersing members as they get older and pursue their opportunities to breed and establish a territory, however. This, in turn, can be affected by varying stochastic conditions in their system that may affect prey availability.

We can make two distinctions in the way that these packs are formed. There are what are normally termed a simple pack, formed of a breeding male and a female and their offsprings, or complex packs which may include offspring from several prior years and thus, creating multi-generational groups. The more complex packs tend to happen where prey is large, such as moose, bison and elk. With simple packs, the parents tend to do all the work as they teach the inexperienced pups to navigate the world around them, and with complex packs, having more experienced members aside from the mating pair, there is room for more division of labor all around. As we can see, these are two completely different dynamics which can profoundly affect and dictate the wolves day to day.

Wolves are extremely territorial and use a wide range of scent marking and posting to signal rival wolf groups’ territory boundaries. They also make long scratches in the dirt after urinating, made by kicking with their hind legs and pulling back with their front legs. Both sexes make these marks, but mainly the males, especially during the mid-winter breeding season.

Wolves use a wide range of vocal communications such as growls, snarls, barks, whining, and, of course, the widely-known howls, which they use to communicate with wolves from their own family or to announce themselves to rival wolves and for the location of prey.

They are social hunters who work cohesively to bring down prey much bigger than themselves. Native prey for Mexican wolves include elk, mule deer, white-tailed deer, javelin, rabbits, and other small mammals. Rick Bass makes note of the traditional native southwestern elk, the Merriam elk, being extinct as a result of overhunting and competition from domestic grazing animals at the turn of the 20th century. Reintroduction attempts brought the northern Rockies elk into the area, which is bigger than Merriam elk and is now common in the southwest. The hunting strategy for wolves is coursing, that is to chase their prey over large distances, and attack from behind and the flanks of the prey species after it has been weakened or worn down.

Each individual may carry out a specific role in the hunt, depending on based on age, gender, and social status. The dominant individuals, typically the breeding pair usually selects the prey and initiate the attack, but may break it off if it its’s going unsuccessfully or a change to another prey if needed. But they don’t necessarily “direct” the hunt. Each wolf seems to know what to do and they do it as one. The group will engange in a series of behaviors that are meant to test their prey for weakness and once any sign of it, they will typically commit to it and move in for an attempted kill.

Trophic niche:

Mexican gray wolves are apex predators, and as such they occupy the top of the trophic pyramid. They are crucial components of their ecosystems for they modulate prey populations and through selectively taking down weaker, older and sick individuals, control prey species population. In his book The Wolf: The Ecology and Behavior of an Endangered Species, Dr. David Mech explains the “sanitation effect” of wolves, holding that the culling of biologically inferior (or less fit) individuals from a population is called the sanitation effect of predation. By predating on diseased animals, wolves can also prevent them from spreading illness and pathogens to the rest of the herd. Wounded, injured, or crippled animals may seem as little detriment to the herd but they are less effective reproducers and contribute little to the overall success of the herd. However, they use as much food and resources, as well as space and cover, as the more effective reproducers. Therefore, their presence takes away from the prime individuals, thus, by removing inferior individuals through predation, wolves unequivocally impart a long range of benefits to the strengthening of the individuals that will pass on their genes.

As apex carnivores, the effects on the ecosystem in which they inhabit reverberate throughout the system in such profound and complex ways that one can argue their presence effects an increase in biodiversity as well, making these systems more functional and resilient. Contrary to popular belief, wolves, as most apex predators, rarely overcome their prey populations. However, surplus killing does indeed occur though often has a contextual explanation and should not be considered as habitual behavior. Surplus killing is a fascinating topic with evolutive adaptive and behavioral scientific explanation to which I plan to explore on another article. We can conclude, then, that with their presence and predatory activity, large carnivores prevent hoofed herbivore mammals (ungulates) from overgrazing entire areas, allowing preferred young tender shoots and plants to propagate and continue to thrive in these areas.

Adaptations for an arid and/or adaptation for the cold

Mexican gray wolves have long legs and sleek bodies that make them very fast in the long chases of ungulates and other prey animals (coursing). The fur colorations serve a great camouflage in the forested areas. Their coat is heavy, oiled, and with a thick undercoat that helps them conserve heat in the winter cold temperatures. From all the images I have seen, and wolves I have watched and observed myself, it seems to me that Canis lupus baileyi has slightly larger ears than the northern gray wolves, which may suggest a manifestation of Allen’s rule. In the late 19th century, Joel Asaph Allen worked out that the average temperature of the ecosystem to which an organism is adapted affects the surface-to-area-volume ratio for their physiology. In broader terms, animals adapted to warmer climates will have larger limbs and appendages than animals adapted to cold climates. Here I am referring to homeotherms; that is, those who can maintain a stable body temperature despite external temperatures i.e. warm-blooded animals. This may be an adaptive eovlutive outcome because of the need to eliminate excess heat from their bodies. With an evolved higher surface area-to-volume ratio to maximize the surface area, it is easier and faster for excess body heat to dissipate and, therefore, they tend to cool off more easily. The opposite would be true for cold-climate organisms.

Reproduction:

Wolves become sexually mature at about two years, with females maturing a bit sooner at around 1 ½ years of age. Around about 2 ½ years of age, usually in mid-winter, they typically form a pair that often lasts for life. However, is one of the pair members dies, the remainder partner will pair up with a new mate.

In Yellowstone, it is not uncommon for the dominant male to mount other subordinate females but this isn't the general rule. What tends to happen is that in certain years, typically in situations where there seems to be an abundance of prey, the dominant female will not engage in the more normal behavior of agression that typically suppresses the estrus cycle of the rest of the females in the group, and this often leads to multiple litters in a year. However, this occurrence, to my knowledge, has been reported mostly in the Yellowstone National Park and I am unsure if it applies to the Mexican wolves in the wilds of the Southwest. The bond formed is, however, very strong and pairs show great affection to each other. In the case where the male may mate, or attempt to mate with other subdominant females, he will usually still remain focused on the dominant female. When females enter estrus, it usually only once per year and the mating takes place over 3-5 days. In the Southwest, this occurs between late December and mid-February.

Before pups are born, the female selects an appropriate den site. The sites are not always nor necessarily selected for their proximity to water. However, a view of the surrounding area of the den is a deciding factor. Once selected, the den site may be used for many years (Bailey, 1931). Den sites are either dug out new under a rock ledge or a base of large tree trunks, or by enlarging already existing cavities, usually on a slope (Young 1944). Dens may have one or several entrances, each one usually marked by a mound of discarded dirt, although the main entrance is well hidden, often in shrubbery or thickets. The entrance is so small that the female must crawl on her belly to enter it. The quarters are a bit more spacious, but not big enough for the adults to stand upright. The quarters may be up to fifty feet from the main entrance. An interesting fact Dr. Wiese shared with me as a sign to look for during breeding observations is plucking of the belly hair from the female. I suspect this is to clear the way for pups to have an easier time latching onto the nipples and facilitate suckling of the mother's milk. If that's the case, then it would mean that this also means that she is close to giving birth.

After a gestation of 60-63 days, typically 4-8 pups will be born in spring (March-April in New Mexico and Arizona). Pups are born blind and they open their eyes between 5-9 days. The female eats any excrement dropped by pups and won’t defecate inside the den herself. They nurse for 6-8 weeks, during which time the male assists by providing food for the female. He seldom enters the den, but he drops food regularly at the entrance and remains on guard during the day from some nearby vantage point. Male wolves are always working to protect their mate and offspring, therefore, if danger approaches, they will lure the intruder by allowing himself to be noticed and take them away from the den site. If one of the mates is killed, the surviving mate will take on the role of single parent and will move the pups to an alternate den.

At about three weeks of age, the pups will venture out of the den. The excursions will gradually become longer and more frequent until about mid-summer when pups spend as much time outside of the den as inside. Leg bones, vertebrae, freshly killed rodents, or skulls are brought for the pups to gnaw on or play with. By late summer the roughly three-to-four-months-old pups leave the den and follow parents continuously.  By October the young wolves are typically already learning to kill with the rest of the family. The surviving young will remain with their parents through the first winter. They attain full size by 9-11 months and by their second winter, young animals are loosely associated with their parents, spending most of their time with siblings or by themselves.

Conservation Efforts and Status:

There was a time when thousands of Mexican gray wolves would have roamed free in the Southwest. The settling of the west and the invasion of cattle and other livestock farming in wolf natural habitat would quickly change this, and conflict arose. This led to an extermination campaign from ranchers sanctioned by the government through different means such as strychnine, compound 1080, jagged-tooth metal traps, guns, dynamite charges in dens, wolf bounties, and anything that would decimate the populations of a species that had rapidly come to be construed to as varmint.

Of the many tactics employed by Wolfers, a particularly atrocious method of extermination was to track the dens and kill all but one pup. They would then chain the surviving pup, commonly referred to as the “Judas” wolf, to a rock or tree. As the tied-down wolf whimpered and howled in calls for the rest of its family, the expectation was that the rest of the wolves would rapidly return so that hidden hunters would shoot all down easily.

Through the indiscriminate killing of wolves, largely to protect livestock special interests and to reduce competition for habitat as well as natural prey, the Southwest lost their last Lobos in the wild by the 1940s. Luckily, Congress passed the creation of the Endangered Species Act in 1973, and shortly after, Mexican wolves were listed as endangered species in 1976.

In 1977, the Department of the Interior charged the USDFW with the task of reintroduction of Mexican wolves to the wild. Between 1977 and 1982 an effort to capture wild remaining Mexican wolves in an attempt to create a captive wolf breeding program was initiated in collaboration with Mexico in a bi-national effort to keep these magnificent canids alive, known as the Species Survival Plan (SSP).

As the capturing and breeding program developed successfully, the team would have to identify a suitable area for the potential release and reintroduction of wolves in the Arizona and New Mexico area, a fraction of its historical range. The Environmental Impact Statement (EIS) was finalized in 1996 and the Apache National Forest (Arizona) and Gila National Forest (New Mexico) were designed as prime areas for the reintroduction to take place. Finally, in March 28th, 1998, the first captive-bred Mexican wolves were released into the wild in the Blue Range Wolf Recovery Area (BRWRA).

Mexican wolf experimental pop area map, USFWS, Public Domain, https://www.fws.gov/media/mexican-wolf-experimental-pop-area-map

 The reintroduction project in the last two decades has had its ups and downs, but fortunately, recent years have shown good results. The United States Fisheries and Wildlife Service (USFWS) reports that at least 59 packs were tracked and documented in 2022 of which 40 roamed the New Mexico part of the wolf territory and 19 in Arizona. The Service also reports a stunning 67 percent survival rate, a significant win considering that pups’ survival rate in the wild tends to be closer to 50 percent. It is notable to mention that the Interagency team continues to practice supplemental feeding techniques, which is likely having an impact on these numbers, but a formidable win nonetheless. I mention this because, depending on who you ask, at this point in the recovery effort, it seems more desirable that the management of this species would be more hands-off by now. Lastly, the recovery team has been able to collar about 109 individuals, allowing them to track about 45 percent of the total population providing the research team with invaluable data.

Current research questions

The genetic study of Lobos both in captivity and the wild is an ongoing research task with many goals other than creating a stable, self-sustaining, population. Among them is to ensure genetic diversity and minimize inbreeding problems.

In 1996, Jaime García-Moreno, Marjorie D. Matocq, Michael S. Roy, Eli Geffen and Robert K.Wayne, published a study hoping to clarify uncertainty concerning the origin of the wolves selected for the captive breeding program initiated by the U.S. Fish and Wildlife Service department in 1984. Three wolves from Durango and Chihuahua (#5, #11, and the unknown wild sire of #6, #7. #8, #9, and #10) were caught in the wild between 1977 and 1980 and designated as the “certified lineage”. This first set later became known as the McBride lineage (P.W. Hedrick and R. J. Fredrickson). To avoid inbreeding depression and to increase genetic variation, more specimens were needed to be added to the program (Laikre and Ryman, 1991). Two other captive populations were then established to complement the gene pool: the Aragón lineage and the Ghost Ranch lineage. The Aragón lineage, at Zoological Park of San Juan de Aragón in Mexico City in 1985 (wolves #209 and #210). The animals’ origins selected for this population were poorly documented (Hedrick 1995). The Ghost Ranch lineage (wolves #293 and #294) was established at the Arizona-Sonora Desert Museum, near Tucson, AZ. There were two founders in this population: the male was bought as a pup by a tourist in the town of Yecora, Sonora (Mexico) and later donated to the museum, and the female founder, was captured from the wild Pack Canyon at the Tumacacori Mountains in southern Arizona in 1959.

The McBride and Ghost Ranch lineages underwent analysis for allozyme and mitochondrial DNA polymorphisms. The results showed that Mexican wolves have a unique mitochondrial haplotype (group of genes within an organism that are inherited from a single parent). Although the analysis of the Ghost Ranch lineage showed that they all had Mexican wolf haplotype, there were still questions in regards to the origin of the male founder (Garcia-Moreno et all). Similar uncertainty raised questions about the origins of the founders of the Aragon lineage as well. The three captive populations of Mexican wolves were established with different founders at different times. None of the surveyed individuals from the uncertified lineages had domestic dog or coyote marker alleles, and both populations had a large proportion of alleles in common with certified wolves, suggesting that they were not simply founded by a cross between a gray wolf and domestic dog or coyote as some critics of the project allege (Garcia-Moreno et all 1996).

After establishing that all the lineages descended from independent founders, both Ghost Ranch and Aragon lineages were incorporated into the captive program management program. The McBride lineage had more founders, a lower inbreeding coefficient, and a greater number of surviving alleles than the other two populations, resulting from intensive management to maintain genetic diversity and minimize inbreeding depression. Because of this, the Genetics Committee of the Mexican Wolf Recovery Team suggested a percentage ratio to follow when future generatins would be incoming from breeding in captivity. They recommended that the combined populations consist of 10% each from Ghost Ranch and Aragon lineages and the rest from the McBride lineage (Hendrick et all 2007).

Despite the closely monitored management of the populations, the captive breeding program has had partial success only. They have slowly accumulated inbreeding and consequently lost genetic variation. At the time of Hendrick and Fredrickson’s published paper, the progress to combine the captive populations had shown success, but it can be argued that the self-imposed rules from the USFWS in not allowing larger restricted areas for reintroduction that had the most negligent impact on the genetic diversity of the populations. This, coupled by the fact that the Service continues to employ subsidized feeding showcases the need for continued support and updating of the proposals to allow wolves the ability to self-sustain by ensuring a healthy availability of wild prey. Because these factors undoubtedly conflicts with livestock growers' interest, the project perception tends to be contentious.

Since the begining of the project, other facilities have since been added to the list of pre-release captive facilities, such as Servilleta (Socorro, NM) and Ladder (Caballo, NM) Ranch Wolf Management Facilities in New Mexico (near the Blue Range Wolf Recovery Area) and Wolf Haven International, in Tenino WA. I was lucky to work as a biological technician at the Ladder Ranch location and volunteer for the Service at the Sevilleta National Wildlife Refuge in 2018 and 2019 and much of the footage and pictures found in this website were taken there.

Sources:

-BOOKS:

The Wolf in the Southwest, The Making of an Endangered Species (David E. Brown, 1983).

The New Wolves (Rick Bass, 1998).

Wolf Haven, Sanctuary and the Future of Wolves in North America (Brenda Peterson and Annie Marie Musselman, 2016).

The Wolf: The Ecology and Behavior of an Endangered Species, (Dr. L. David Mech, 1970)

Mammal Tracks and Signs: A Guide to North American Species, (Mark Elbroch, 2003)

-ACADEMIC JOURNALS: 

HEDRICK, P.W. and FREDRICKSON, R.J. (2007) ‘Captive breeding and the reintroduction of Mexican and red wolves’, Molecular Ecology, 17(1), pp. 344–350. doi:10.1111/j.1365-294x.2007.03400.x.

García‐Moreno, J. et al. (1996) ‘Relationships and genetic purity of the endangered Mexican wolf based on analysis of microsatellite loci’, Conservation Biology, 10(2), pp. 376–389. doi:10.1046/j.1523-1739.1996.10020376.x.

-INTERNET SOURCES

-Fish and Wildlife Service official webpage: (www.fws.gov/southwest/es/mexicanwolf)  

-Wolf Haven International: (http://wolfhaven.org)

-Lobos of the Southwest: (http://mexicanwolves.org)