# Volcano rabbit

The volcano rabbit (Romerolagus diazi), also known as the teporingo, zacatuche, or burrito, is a small rabbit in the family Leporidae that resides on the slopes of volcanoes in Mexico. It is the only species in the genus Romerolagus, and is the world's second-smallest rabbit, second only to the pygmy rabbit. It has small rounded ears, short legs, a large forehead, and short, thick fur. It weighs approximately 390–600 g (0.86–1.3 lb) and has a life span of 7 to 9 years. The volcano rabbit lives in groups of 2 to 5 animals in burrows (underground nests) and runways among grass tussocks. The burrows can be as long as 5 m and as deep as 40 cm. There are usually 2 to 3 young per litter, born in the burrows. In semi-captivity, however, they do not make burrows and the young are born in nests made in the grass tussocks.
Unlike many species of rabbits (and similar to pikas), the volcano rabbit emits high-pitched sounds instead of thumping its feet on the ground to warn other rabbits of danger. It is crepuscular and highly active during twilight, dawn and all times in between. Populations have been estimated as approximately 1,200 individuals in 150–200 colonies over their entire range.

## Taxonomy and etymology

Romerolagus diazi was first described by the head of the Mexican Geographical and Exploring Commission, Fernando Ferrari-Pérez, in 1893 as a member of the hares (genus Lepus), using the scientific name Lepus diazi and common name conejo del Volcán (volcano rabbit). Its type locality was "near San Martín Texmelusán, northeastern slope of Volcán Iztaccíhuatl [Ixtaccíhuatl, Puebla], Mexico". It was separately described as the Popocatepetl rabbit, Romerolagus nelsoni, in 1896 by Clinton Hart Merriam in an account that made no reference to the earlier work of Ferrari-Pérez. The article noted a type specimen that was collected at "Mt. Popocatepetl, Mexico (altitude 3,350 meters or 11,000 feet)" by Edward William Nelson, for whom the species was named. Merriam noted several characteristics that differed significantly from any member of the hares, such as its anatomy and means of locomotion (running on all four legs rather than hopping), and gave it the genus name Romerolagus in honor of Matías Romero, a supporter of the United States Biological Survey in Mexico. It was given its current common and scientific names by Gerrit Smith Miller Jr. in 1911, who noted the discrepancy between the two descriptions and, after consulting with Nelson and Ferrari-Pérez, clarified the nomenclature of the species.
The volcano rabbit is named for its preferred habitat, that being the slopes of volcanoes. One Nahuatl name, zacatochtle, refers to the rabbit's relationship with subalpine tussock grass in the genus Festuca (referred to as zacate in Spanish, zacatl in Nahuatl). The name comes from the combination of zacatl and tochtle ("rabbit"), and has been modified to the currently-used epithet zacatuche. Another common name, teporingo, likely derives from Classical Nahuatl, combining tepētl ("mountain"), olīn ("movement") and the suffix -co referring to location.
No subspecies of the volcano rabbit are recognized, and it is the only species within its genus, though there have been few genetic studies of the disconnected populations that would elucidate such relationships.

## Description

The volcano rabbit's adult weight ranges from 386 to 602 g (0.851 to 1.327 lb). It has short, dense fur that ranges in color from brown to black. The rabbit is a gnawing animal that is distinguished from rodents by its two pairs of specialized upper incisors. Its body size and hindlimb development demonstrates a need for grass cover to evade predators. Its speediness and hind limb development relative to its body size correlates to a need for evasive actions. It is relatively slow and vulnerable in open habitats; therefore it takes comfort in high, covered areas. Volcano rabbits have a very narrow gestational period: In one study, all females gave birth between 39 and 41 days after coitus. It has difficulty breeding in small enclosures.
The volcano rabbit creates runways similar to those made by microtine rodents to navigate their habitat. Its burrows consist of dense grass clumps, with a length of 5 m and depth of 40 cm. Its small size relates to its selective dietary habits.

## Distribution and habitat

Volcano rabbits are endemic to Mexico. Specifically, the rabbit is native to four volcanoes just southeast of Mexico City. The largest of these volcanic regions is within the Izta-Popo National Park, with other areas including the Chichinautzin and Pelado volcanoes. The range of the volcano rabbit has been fragmented into 16 individual patches by human disturbance. Vegetation within these patches is dominated by native grasslands and include Nearctic and Neotropical varieties. The elevation of these patches is between 2900 and 3660 meters above sea level. The soil consists mostly of andosols and lithosols. The local climate is temperate, subhumid, and has a mean annual temperature of 11 °C. Annual rainfall averages at about 1,000 millimetres (39 in). In those patches most heavily populated with volcano rabbits, the plants Festuca tolucensis and Pinus hartwegii are most abundant. Volcano rabbits show strong preferences for habitat types that are categorized as open pine forests, open pine woodland, and mixed alder pine forest. Human activity in the area has had a great impact upon the preferred habitat of the volcano rabbit, as humans have fragmented the rabbit's habitat by constructing highways, farming, afforestation, and lack of sound fire and grazing practices. Ecological fragmentation has been caused by environmental discontinuity.
Volcano rabbits are commonly found at higher altitudes. Almost 71% of volcano rabbits are found in pine forests, alder forests, and grasslands. Volcano rabbits are more abundant near tall, dense herbs and thick vegetation, and are adversely affected by anthropogenic environmental disturbances like logging and burning. A study on the effects of climate change upon volcano rabbit metapopulations concluded that fluctuations in climate affected rabbits more on the edge of their habitable range. The volcano rabbit's range encompasses a maximum of 280 km$^2$ of grasslands in elevated areas in the Trans-Mexican Neovolcanic Belt.
Research conducted by Hoth et al., in relation to the distribution of the Volcano Rabbit in 1987 found no records of this species in the Nevado de Toluca, including the site where Tikul Álvarez (IPN) collected a specimen in 1975 (Nevado de Toluca, 4 km S, 2 km W Raíces, 3350 masl). Though there was an unconfirmed sighting in the region in August 2003, no permanent volcano rabbit colony has been documented in Nevado de Toluca and it was declared "extinct" within this portion of its range in 2018; populations exist elsewhere within the Trans-Mexican Volcanic Belt and in captivity. The International Union for the Conservation of Nature no longer mentions the Nevado de Toluca as a current or potential site for the distribution of this species.

### Habitat management

The IUCN/SSC Lagomorph Specialist Group has created an action plan for this rabbit that focuses upon the need to manage the burning and overgrazing of its Zacatón habitats and to enforce laws prohibiting its hunting, capture, and sale. Studies about the volcano rabbit's geographical range, role in its habitat, population dynamics, and evolutionary history have been recommended.

## Diet

The volcano rabbit feeds primarily on grasses such as Festuca amplissima, Muhlenbergia macroura, Stipa ichu, and Eryngium rosei. The rabbits also use these plants as cover to hide from predators. M. macroura was found to be in 89% of pellets of the volcano rabbits, suggesting that this is the base of their diet, but it does not actually provide the necessary energy and protein needs of the rabbits. By supplementing their diet with 15 other forms of plant life, volcano rabbits can get their required nutrition. Other plant species that support the volcano rabbit are Muhlenbergia quadidentata, Pinus hartwegii, F. tolucensis, and P. hartwegeii. Volcano rabbits also consume leaves, foliage, and flowers indiscriminately under poor conditions, as habitat loss has eliminated much of their food sources. Protein acquisition is the primary limiting factor on the size of the populations of each of the four volcanoes on which the species is located. Studies show that many individuals of the population suffer from serious weight loss and starvation.
Seasonal changes also affect the diet of the volcano rabbit greatly. The grasses it normally consumes are abundant during wet seasons. During the dry season, the volcano rabbit feasts on shrubs and small trees, as well as other woody plants. During the winter plants, these woody plants make up most of their diet, as well as the primary building material for their nests.

## Conservation

Threats to R. diazi include logging, harvesting of grasses, livestock grazing, habitat destruction, urban expansion, highway construction and frequent forest fires. Unsound management policies of its habitat in National Parks and outside, mainly by afforestation, have also threatened volcano rabbit populations. These threats have resulted in a loss of 15–20% of the volcano rabbit's habitat during the last three generations. They have also resulted in ecological displacement and genetic isolation of R. diazi.
Hunting is another threat to the volcano rabbit, despite the fact that R. diazi is listed under Appendix 1 of CITES and it is illegal to hunt under Mexican law. Many are unaware that R. diazi is protected and officials do not adequately enforce its protection. Hunting, livestock grazing, and fires can even harm R. diazi within national parks that are protected such as Izta-Popo and Zoquiapan National Parks.
In terms of conservation efforts, various captive breeding programs have been established with relative success, but infant mortality in captivity is high. Actions toward conservation should be focused on the enforcement of laws which forbid hunting and trading of the volcano rabbit. Furthermore, efforts must be put toward habitat management, specifically the control of forest fires and livestock overgrazing of grasses. Lastly, it would be beneficial to enact education programs regarding R. diazi and the various threats that face it. The public should also be educated about the volcano rabbit's protected status, as many are unaware that it is illegal to hunt R. diazi.

### Decline

Numerous studies conducted during the 1980s and 1990s agreed that the habitat of the volcano rabbit was shrinking due to a combination of natural and anthropogenic causes. There is evidence that its range has shrunk significantly during the last 18,000 years due to a 5–6 °C (41–43 °F) increase in the prevailing temperature, and its distribution is now divided into 16 patches. The fragmentation of the volcano rabbit's distribution has resulted from a long-term warming trend that has driven it to progressively higher altitudes and the relatively recent construction of highways that dissect its habitat.
Declines in the R. diazi population have been occurring due a number of changes in vegetation, climate, and, thus, elevation. The volcano rabbit is extremely vulnerable to the effects of climate change and other anthropogenic intrusions because of its extremely limited range and specialized diet. Patches of vegetation that R. diazi uses for survival are becoming fragmented, isolated and smaller, rendering the environment more open and therefore less suitable for its survival. Because the volcano rabbit inhabits the area surrounding Mexico City, Mexico's most populous region, it has suffered a very high rate of habitat destruction.
The cottontail rabbit, Sylvilagus, is expanding into the volcano rabbit's niche, but there is "no evidence that [volcano rabbits'] habitat selection is a response to competitive exclusion." The volcano rabbit has been severely pressured by human intrusion into its habitat. Anthropogenic disturbance enables other rabbit species to flourish in grasslands, increasing competition with the volcano rabbit.
Volcano rabbits have been bred in captivity, but there is evidence that the species loses a significant amount of genetic diversity when it reproduces in such conditions. A comparative study done on wild and captive volcano rabbits found that the latter lost a substantial amount of DNA loci, and some specimens lost 88% of their genetic variability. There was, however, one locus whose variability was higher than that of the wild population.