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Perognathus merriamiMerriam's pocket mouse

By Hunter Folmar

Geographic Range

Perognathus merriami (Merriam’s pocket mouse) currently occupies a geographic range extending from the plains of northern Texas and western Oklahoma, westward to eastern New Mexico, and south through western and southern Texas into the Mexican states of Chihuahua, Nuevo Leon, Tamaulipas, and Coahuila. Merriam’s pocket mouse does not extend eastward past the western two-thirds of the state of Texas. (Best and Skupski, 1994; Linzey, et al., 2008; Schmidly, 2004)

Habitat

Merriam’s pocket mice inhabit several different vegetation and habitat types throughout their range. In central and southern Texas they live in shortgrass or heavily grazed pasture dominated by mesquite (Prosopis glandulosa). In western regions, they inhabit desert scrubland characterized by rocky soil and limited vegetation. Merriam’s pocket mice appear to have no preference for soil type within its geographic range, residing in areas of clay, caliche, and sand. (Best and Skupski, 1994; Chapman and Packard, 1974)

  • Range elevation
    0 to 1585 m
    0.00 to 5200.13 ft

Physical Description

Merriam’s pocket mice are small heteromyid rodents whose weight and length (including body and tail) averages from 7 to 10 grams and 113.9 to 116.4 mm, respectively. Average weight and size varies depending on geographic region. Within Texas, for example, this species is smallest in the south, moderate in size in the west, and the largest in north. Males are slightly larger in size. For example, in Coahuila, Mexico an average difference of 0.9 grams between males and females has been reported. Throughout its range, the pelage of P. merriami is smooth and silky, and when pressed down may be oily in appearance. The dorsal side of the pelage is ochraceous buff colored with black hairs; the ventral side is solid white. Merriam’s pocket mice are morphologically distinguishable from other pocket mice in the genus (such as Perognathus flavus) by its shorter mastoid breadth, shorter bullar length, slightly smaller hind foot, longer average tail length, and a relatively small post-auricular white spot. No data on metabolic rate was found for P. merriami. However, Perognathus flavus, the sister species to P. merriami, has a basal metabolic rate of 2.09 cc O2/g hr.

Recent genetic analyses has confirmed the diagnosis of P. merriami as a sister species to P. flavus, despite earlier reports indicating P. merriami and P. flavus are conspecific based on behavioral analyses. Two subspecies of P. merriami are currently recognized: P. m. gilvus in the northwestern portion of its range and P. m. merriami in the southeastern portion of its range. (Best and Skupski, 1994; Brant and Lee, 2006; Coyner, et al., 2010; Genoways and Brown, 1993; Martin, 1977)

  • Sexual Dimorphism
  • male larger
  • Range mass
    7 to 10 g
    0.25 to 0.35 oz
  • Range length
    113.93 to 116.43 mm
    4.49 to 4.58 in
  • Average basal metabolic rate
    2.09 cm3.O2/g/hr

Reproduction

The mating system of Merriam’s pocket mouse is not known. However, it is likely that this species exhibits similar mating systems as what is observed in other species of Perognathus and Chaetodipus. These heteromyid genera are closely related, and both belong to the subfamily Perognathinae. Because of larger home range observations for males than females, such as in C. formosus and P. parvus, and larger mean capture distance in P. longimembris, it is assumed P. merriami exhibit polygynous or promiscuous mating systems. (Genoways and Brown, 1993)

The breeding season of Merriam’s pocket mouse ranges from April to November, with some individuals producing two litters per season in southern portions of its range. The mass at birth is unknown. However, P. longimembris has a neonate weight of 0.9 grams and although this Perognathus species is larger than P. merriami, birth mass may be similar. Typical litters usually consist of three to six individuals, and young retain a soft, yellow colored pelage that lacks the black hairs that are present on the dorsal side of adults. The gestation period is unknown for Perognathus merriami; P. flavus, its sister species, has a gestation period of 26.0 days. It is therefore likely that P. merriami has a similar gestation time.

Young males may molt into adult pelage and be sexually mature before reaching the final mass of an adult. Females, however, do not appear to be reproductively viable when they are the same mass as a viable juvenile male. Gestation, birth mass, time to weaning, time to independence, and reproductive ages for both sexes of P. merriami are not known at this time. (Best and Skupski, 1994; Chapman and Packard, 1974; Genoways and Brown, 1993)

  • Breeding interval
    Merriam's pocket mice breeds one to two times a year, depending on the range.
  • Breeding season
    April to November
  • Range number of offspring
    3 to 6
  • Average gestation period
    26 days

Parental investment is unknown; no data were available for the Merriam’s pocket mouse or other Perognathus species.

Lifespan/Longevity

Perognathus merriami has a relatively short lifespan, with averages in the wild spanning from 22 to 33 months. Captive individuals have lived for up to three years on limited diets and no water. (Chapman and Packard, 1974; Schmidly, 2004)

  • Range lifespan
    Status: wild
    33 (high) months
  • Range lifespan
    Status: captivity
    3 (high) years
  • Typical lifespan
    Status: wild
    22 to 33 months

Behavior

Merriam’s pocket mice maintain a system of burrows within their home ranges. Males typically maintain six to seven burrows per individual, while females appear to keep around five, on average. They prefer to dig the burrows at the bases of bunchgrasses or other vegetation to add stability to the entrance of the tunnel. Merriam’s pocket mice often have two types of burrows: a refuge and home burrow. Home burrows are much larger, with enlarged nest chambers and two entrances; refuge burrows have one entrance, are shorter in length, and have smaller chambers. Merriam’s pocket mice are nocturnal and remain in the burrow until sundown. Heteromyid rodents are generally thought to avoid contact with other conspecifics, with most encounters (with the exception of mating) lacking in physical contact. (Best and Skupski, 1994; Chapman and Packard, 1974; Genoways and Brown, 1993)

  • Range territory size
    300 to 21,900 m^2

Home Range

Merriam’s pocket mice occupy territories between 0.03 and 2.19 ha depending on the sex of the individual, with females typically occupying larger areas, but males tending to travel farther outside of their territories than females. Territory ranges are roughly equal to home ranges, and territories of Merriam’s pocket mice do not overlap each other, a strong indicator of territorial behavior. (Best and Skupski, 1994; Chapman and Packard, 1974)

Communication and Perception

Little information exists on communication in Merriam's pocket mice, as they normally emit no sound. However, they produce a high-pitched squeak when handled. Other members of Heteromyidae use olfactory communication to exchange information at burrowing and sandbathing sites. Some species, such as Dipodomys spectabilis, have been observed drumming their feet on the ground as a means of communication. No records of this behavior have been recorded in P. merriami. (Best and Skupski, 1994; Genoways and Brown, 1993)

Food Habits

Perognathus merriami typically maintains a diet of seeds, but may consume insects and vegetation. Plant species it has been known to consume include honey mesquite (Prosopis glandulosa), little bluestem (Schizachyrium scoparium), and coastal sandbur (Cenchrus spinifex), among many others. The mouse appears to forage for its food based on seasonal abundance, but will discriminate based on palatability. Merriam's pocket mice do not drink water, obtaining all of the moisture needed from its food sources. (Best and Skupski, 1994; Chapman and Packard, 1974; Schmidly, 2004)

  • Animal Foods
  • insects
  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit

Predation

Merriam's pocket mice are preyed upon by northern grasshopper mice (Onychomys leucogaster), gray foxes (Urocyon cinereoargenteus), loggerhead shrikes (Lanius ludovicianus), and barn owls (Tyto alba). (Best and Skupski, 1994; Raun, 1960)

Ecosystem Roles

Little is known of major effects of P. merriami on its environment. Merriam’s pocket mice act as hosts to multiple species of ectoparasites ranging from mites (Androlaelaps fahrenholzi), fleas (Orchopeas leucopus), ticks (Amblyomma americanum), and lice (Fahrenholzia boleni). Endoparasites obtained from P. merriami include the coccidian Eimeria reedi.

Merriam’s pocket mice occur in environments that are sympatric with Baiomys taylori, Chaetodipus hispidus, C. nelsoni, C. penicillatus, Dipodomys merriami, Perognathus flavus, and Sigmodon hispidus. (Best and Skupski, 1994; Chapman and Packard, 1974; Genoways and Brown, 1993)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Merriam’s pocket mice can be kept as pets in suitable enclosures filled with slightly damp sand. They should be fed seeds occasionally. Other than being kept as pets, there are no known positive effects of P. merriami on humans. (Best and Skupski, 1994)

Economic Importance for Humans: Negative

Merriam’s pocket mice are reservoirs for diseases that have the potential to be transmitted to humans. They carry hantaviruses albeit at low frequencies. (Mantooth, et al., 2001)

Conservation Status

Merriam’s pocket mice appear to be stable due to their large range and sizeable population with no major conservation concerns at this time. (Linzey, et al., 2008)

Contributors

Hunter Folmar (author), Texas A&M University, Jessica Light (editor), Texas A&M University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chemical

uses smells or other chemicals to communicate

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

folivore

an animal that mainly eats leaves.

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

omnivore

an animal that mainly eats all kinds of things, including plants and animals

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Best, T., M. Skupski. 1994. Perognathus merriami. Mammalian Species, 473: 1-7.

Brant, J., T. Lee. 2006. Morphological analysis of Perognathus flavus and P. merriami (Rodentia: Heteromyidae). The Southwestern Naturalist, 51(1): 79-86.

Chapman, B., R. Packard. 1974. An ecological study of Merriam's pocket mouse in Southeastern Texas. The Southwestern Naturalist, 19(3): 281-291.

Coyner, B., T. Lee, D. Rogers, R. Bussche. 2010. Taxonomic status and species limits of Perognathus (Rodentia: Heteromyidae) in the southern Great Plains. The Southwestern Naturalist, 55(1): 1-10.

Genoways, H., J. Brown. 1993. Biology of the Heteromyidae. Provo, Utah: The American Society of Mammalogists.

Lee, T., M. Engstrom. 1991. Genetic Variation in the Silky Pocket Mouse (Perognathus flavus) in Texas and New Mexico. Journal of Mammalogy, 72(2): 273-285.

Linzey, A., R. Timm, S. Álvarez-Castañeda, I. Castro-Arellano, T. Lacher. 2008. "Perognathus merriami" (On-line). The IUCN Red List of Threatened Species. Accessed October 03, 2015 at http://www.iucnredlist.org/details/16637/0.

Mantooth, S., M. Milazzo, R. Bradley, C. Hice, G. Ceballos, R. Tesh, C. Fulhorst. 2001. Geographical distribution of rodent-associated hantaviruses in Texas. Journal of Vector Ecology, 26: 7-14.

Martin, R. 1977. Species preferences of allopatric and sympatric populations of silky pocket mice, genus Perognathus (Rodentia: Heteromyidae). American Midland Naturalist, 98(1): 124-136.

Osgood, W. 1900. Revision of the pocket mice of the genus Perognathus. North American Fauna, 18: 1-73.

Raun, G. 1960. Barn owl pellets and small mammal populations near Mathis, Texas, in 1956 and 1959. The Southwestern Naturalist, 5(4): 194-200.

Schmidly, D. 2004. The Mammals of Texas. Austin, Texas: University of Texas Press.

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