Microtus pinetorum - Pine Vole

Geographic Range:

Range of M. pinetorum in Wisconsin is limited to the southern portion of the state with isolated occurrences in central Wisconsin (Long 1990).  M. pinetorum is extant throughout the eastern United States and an extreme southern portion of Ontario.  Its southern range is limited to approximately 30 degrees north latitude with a small protrusion into north-central Florida.  The western edge of its range is less precise and variable.  It is known to live in eastern Texas, Oklahoma, and Kansas, as well as the southeastern tip of Nebraska, the southeastern 2/3 of Iowa and the extreme southeastern tip of Minnesota (Smolen 1998).  

Physical Description:

M. pinetorum is observed as having even length, reddish or “walnut brown” fur, that is short and dense like that of a mole.  It has an exceptionally small tail and exceptionally large fore claws that are elongated to fit M. pinetorum’s semi-fossorial lifestyle (Long 1990).  Along with these characters, Kurta (1995) adds that M. pinetorum has very short ears and reduced eyes.  Furthermore, its tail is no longer than its hind foot.

Long (1990) considers the skull of M. pinetorum to be broad, “…especially the posterior extensions of the nasals, the adjacent premaxillaries, and the interorbital region.”  He also views the post-rostral portion of the skull as being quite circular, with the brain case encroaching into the orbits, and considers the nasals short and broad.

The dental formula for M. pinetorum is i1/1, c0/0, p0/0, m3/3, total 16 (Smolen 1981).  Teeth of M. pinetorum are similar to M. ochrogaster.  However, the first inner prism of the middle ventral molar is normally quadrate and angles sharply (Long 1990).

Jackson (1961) gives these basic measures of M. pinetorum:  Total length of adults, 110 to 132 mm.  (4.3 to 5.2 inches); tail, 18 to 25 mm.  (0.7 to 1.0 inches); ear from notch, 7 to 9 mm. (0.3 to 0.4 inches); hind foot, 16.5 to 18 mm. (0.6 to 0.7 inches).  Weight of adult, 24 to 30 grams. Skull length, 22.5 to 25.4 mm.; width, 13.5 to 15.5 mm.; upper molariform tooth row, 6.2 to 6.6 mm.

These characters are relatively unique to M. pinetorum and easily set apart this species from confusion with any other rodents in Wisconsin (Kurta 1995).

Lifespan/Longevity:

According to Kurta (1995) M. pinetorum usually only lives to an age of about 3 months in the wild, and its maximum age is little over a year.  Smolen (1981) cites a paper by Miller and Getz published in 1969 that found an average survival length of 2.6 months.

Predation:

There are many predators that feed on M. pinetorum, mainly those animals that are considered to be rodent specialists.  Kurta (1995) lists numerous hawks and owls as being predators as well as snakes, foxes, raccoons, weasels, skunks and opossums. Smolen (1981) compiled a list of specific species known to prey on M. pinetorum:

Barn Owl                     (Tyto alba)

Long–eared Owl          (Asio otus)

Screech Owl                (Otus asio)

Short-eared Owl          (Asio flammeus)

Great Horned Owl        (Bubo virginianus)

Barred Owl                  (Strix varia)

Red-tailed Hawk          (Buteo lineatus)

Broad-winged Hawk    (Buteo platypterus)

Marsh Hawk                (Circus cyaneus)

Pilot Black Snake         (Elaphe obsolete)

Red Fox                       (Vulpes fulva)

Grey Fox                      (Urocyon cinereoargenteus)

Opossum                      (Didelphis marsupialis [virginiana])

Ecosystem Roles:

M. pinetorum plays a relatively small role in the ecosystem, especially in Wisconsin due to its limited distribution throughout the state.  Other than being a prey item for predators, I could find no evidence of M. pinetorum playing any substantial role in the ecosystem.

Food Habits:

M. pinetorum is a generalist herbivore that exhibits the ability to socially transmit food preferences (Solomon 2002).  Roots, tubers, and rhizomes are common food staples for M. pinetorum during much of the year.  In summer months it adds grass stems, clover sprouts, fruits, seeds, and nuts to this diet.  As autumn and winter approach M. pinetorum caches foodstuffs in subterranean chambers.  However, M. pinetorum usually must eat bark to sustain itself through the last months of winter (Kurta 1995).

Reproduction:

Marfori et al. (1997) found DNA evidence among communities of M. pinetorum that is indicative of a monogamous mating system.  Kurta (1995) also says M. pinetorum is monogamous, and the father helps rear the young while sharing the same nest and home range with the mother.  There is a common assumption among mammalogists that M. pinetorum is a cooperative breeder that lives in extended families (Marfori et al. 1997, Solomon 1994).

Solomon and Vandenbergh found their breeding colonies of M. pinetorum had relatively smaller litter sizes than other arvicoline rodents.  However, were still very successful breeders, having, on average, a litter per month for more than 12 months (1994).  In contrast, Kurta (1995) writes that breeding in the wild only lasts from January to October, allowing an adult female to have only four litters.  He also points out that M. pinetorum only has four mammae, which is fewer than other voles, thus most litter contain only 2-4 young.  This coincides with Solomon and Vandenberghs assertion that M. Pinetorum has relatively smaller litter sizes than other arivcoline rodents.

Kurta (1995) writes that young are born weighing 2-3g, after an in utero gestation period of 20-24 days.  Furthermore, the young are born naked but develop short hairs by day 5 and their eyes and ears begin to open by day 8, they are walking by day 12.  According to Smolen (1981) young cease nursing by day 16 and begin to eat solid food. Additionally, lactation generally lasts only 20 days and the pups are usually weaned within 17-21 days.

Male M. pinetorum begin to produce sperm by 6 to 8 weeks, while females become mature at 10-12 weeks, or on average in 105 days (Smolen 1981).  This is comparable to Kurta’s(1995) assertion that “A female [M. pinetorum] dos not conceive until 14-15 weeks of age- much later than either a [M. pennsylvanicus or ochrogaster].”

Behavior:

 McGuire and Sullivan (2001) observed that young M. pinetorum attach to their mothers nipple immediately after she enters the nest and most often stay attached to that nipple until removed by the mother or dislodged, rarely do the young voluntarily release a nipple.  They state that of the four nipples present on M. pinetorum, the young show a distinct preference to suckle on the posterior set.  By observing M. pinetorum in a lab setting McGuire and Sullivan also found that M. pinetorum mothers most commonly dislodge suckling young by spinning in tight circles.

M. pinetorum is a social vole (Solomon 1999).  Powell and Fried (1992) observed Juvenile M. pinetorum exhibiting behavioral activities that are common among helpers in cooperative breeding species.  These behaviors include brooding, grooming, and retrieving younger siblings, and maintaining nests, runways, and food caches.  It is their belief that cooperative breeding has evolved in M. pinetorum because of the limited vacant tunnel networks and the high cost of digging new systems restrains M. pinetorum from rapid dispersal, as in other rodents.

Marfori et al. (1997) found evidence that offspring beyond weaning remain philopatric while the parents continue to reproduce and wean successive litters.  In 1998 Solomon et al. reinforced this idea stating that in their study “… as long as the breeding female remains at the nest, no other female begins to reproduce.”  Brant et al. (1998) proposes that mother M. pinetorum tugging on their daughters could lead to subordination of the daughters thus causing a delay in reproductive activation, preventing pair bonding or sexual behavior.

M. pinetorum has a relatively small home range and shows no evidence of territoriality  (Smolen 1981).  While foraging along surface runways or underground tunnels it never wanders more than 15 or 30 meters away from its nest.  Leaf litter and grasses usually cover its runways. Its tunnel system is generally 3 cm in diameter and 5–10 cm underground (Kurta 1995).  Smolen (1981) hypothesized that the depth and length of tunnels may depend on the depth of loam in their habitat.  He also agreed with Kurta in that M. pinetorum commonly incorporates old mole runways into its tunnel system.  Kurta (1995) and Smolen (1981) both describe nests of M. pinetorum as being globular and most commonly found in the burrow system however, are occasionally found under fallen logs.  Smolen describes nests mainly constructed from dry grasses, leaf fragments, and a few entire leaves, that are 15-18 cm in diameter.  He also found that there are normally 3-4 exits leading away from the nest.

This species is diurnal, thus equally active day or night (Smolen 1981, Kurta 1995).

Habitat:

 M. pinetorum inhabits a range of different habitat types.  Kurta (1995) vaguely describes M. pinetorum’s habitat, “This species prefers hardwood forests of oak, maple, and beech, although it is a potential resident of any wooded area- deciduous, coniferous, or mixed.”  He goes on to say that M. pinetorum requires a sandy soil that is well drained, with a cover of thick duff.  Smolen (1981) concurs with Kurta, finding that well drained soil with a thick ground cover of either litter or vegetation are common parameters in most habitats for M. pinetorum.  Kurta’s vague description may not be unwarranted, Smolen (1981) puts it this way, “Populations of Microtus pinetorum occur in a wide variety of habitats throughout their range, varying from subclimax beech-maple forests with closed canopies and varying depths of leaf litter to grassy fields with many bushes, patches of brambles, and mats of honeysuckle.”  According to Smolen (1981) the floral assemblage for M. pinetorum in Wisconsin is maple (Acer spp.), elm (Ulmus spp.), yellow birch (Betula allegheniensis), basswood (Tilia spp.), and the ferns.  However, it would not be wise to restrict M. pinetorum just to this cover type in Wisconsin due to its ability to live in such a wide range of habitats.

Food Habits:

Positive-

It is relatively easy to breed and maintain a colony of M. pinetorum in the laboratory.  Because M. pinetorum is unique among other rodents in exhibiting a cooperative breeding system as well as displaying fossorial adaptations (Solomon 1994) it can be stated that M. pinetorum has an economic importance simply in its ability to aid research.
      

Negative-

As Smolen (1981) puts it, “Microtus pinetorum has a long history of economic conflict with man.” M. Pinetorum is commonly found in orchards and nurseries, it consumes crops of white and sweet potatoes, peanuts, lily bulbs, nursery stock, and planted seeds (Smolen 1981, Kurta 1995). M. pinetorum is capable of completely girdling apple trees up to six inches in diameter, by the time the nursery realizes what’s happened the trees are usually past recovery (Smolen 1981). Smolen (1981) cites an orchard in West Virginia where over 1000, 18-year-old trees were killed in a single year.  Charles Elton’s book, Voles, Mice and Lemmings (1965) describes “plagues” and “outbreaks” of M. pinetorum, in the early 1900’s, where hundreds of thousands of dollars of damage was done to orchards on the east coast.

The main control of M. pinetorum is accomplished by poisons.  However, successful application can be a significant problem due to M. pinetorum’s semifossorial lifestyle (Smolen 1981).  Measures to control populations of M. pinetorum in orchards should not be limited to one time removal of the pest because M. pinetorum actively invades areas that have reduced populations (Lapasha 1994).

Conservation:

Wisconsin’s Department of Natural Resources considers M. pinetorum to be threatened in the state.  It is protected under state law.

Literature Cited:

Brant, C.L., T.M. Schwab, J.G. Vandenbergh, R.L. Schaefer and N.G. Solomon.  1998.  Behavioural suppression of female pine voles after replacement of the breeding male.  Animal Behaviour 55:615-627.

Elton, C.  1965.  Voles, Mice and Lemmings: 109-113 in J. Cramer and H.K. Swann ed.  Wheldon & Wesley, LTD.  Stechert-Hafner Service Agency, INC. Codicote, Herts. New York, N.Y.

Kurta, A.  1995.  Woodland Vole Microtus Pinetorum.  Mammals of the Great Lakes Region: Revised Edition. The University of Michigan Press, Ann Arbor, Michigan.

Lapasha, D.G. and R.A. Powell.  1994.  Pine vole (Microtus pinetorum) movement in apple orchards with reduced populations.  Journal of Horticultural Science 69:1077-1082.

Long, C.A.  1990.  Voles and Bog Lemmings of Wisconsin.  Wisconsin Academy of Sciences, Arts and Letters.

Marfori, M.A., P.G. Parker, T.G. Gregg, J.G Vandenbergh and N.G. Solomon.  1997.  Using DNA fingerprinting to estimate relatedness within social groups of pine voles.  Journal of Mammalogy 78:715-724.

McGuire, B. and S. Sullivan.  2001.  Suckling behavior of pine voles (Microtus pinetorum).  Journal of Mammalogy 82:690-699.

Powell, R.A. and J.J. Fried.  1992.  Helping by juvenile pine voles (Microtus pinetorum), growth and survival of younger siblings, and the evolution of pine vole sociality.  Behavioral Ecology 3:325-333.

Solomon, N.G., C.S. Yeager and L.A. Beeler.  2002.  Social transmission and memory of food preferences in pine voles (Microtus pinetorum).  Journal of Comparative Psychology 116:35-38.

Solomon, N.G. and J.G. Vandenbergh.  1994.  Management, breeding, and reproductive performance of pine voles.  Laboratory Animal Science 44:613-617.

Solomon, N.G., J.G. Vandenbergh and W.T. Sullivan Jr.  1998.  Social influences on intergroup transfer by pine voles (Microtus pinetorum).  Canadian Journal of Zoology 76:2131-2136.

Solomon, N.G., M.H. Ferkin and R. O’Boyle.  1999.  Do pine voles (Microtus pinetorum) use numerous types of olfactory cues to discriminate gender?  Journal of Chemical Ecology 25:2147-2159.

Smolen, M.J.  1998.  Microtus pinetorum.  Mammalian Species 147:1-7.

 
Reference written by Jeff Houghton, Biol 378: Edited by Chris Yahnke. Page last updated 4-28-04.