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Overview

Brief Summary

Description

"The Sonoma Tree Vole nests so high in trees that finding one in a forest interior is quite difficult, and many records are from individuals that were living in trees that were cut down. A few coniferous tree species provide all of the Sonoma Tree Vole's food. The animal may eat an average of about 2,400 needles per day, taking them from young, terminal twigs and consuming only the outer part of each needle. Although one large tree may have several nests, each nest will usually contain only one Vole. Litters are small—often only one or two young—and the young develop slowly, not leaving the nest until they are a month old. The animal's distribution is limited to the coast of northern California, where it is common."

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  • Original description: Johnson, M.L., and S.B. George, 1991.  Species limits within the Arborimus longicaudus species-complex (Mammalia: Rodentia) with a description of a new species from California.  Contributions in Science (Los Angeles), 429:12.
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Distribution

endemic to a single state or province

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: (5000-20,000 square km (about 2000-8000 square miles)) This vole inhabits northwestern California, from Freestone, Sonoma County, north through Mendocino, Humboldt, and western Trinity counties to the South Fork of the Smith River, Del Norte County (Johnson and George 1991). There is some disagreement over the specific identity (pomo versus longicaudus) of tree voles at the northern extent of the range in northern California (see Hayes 1996).

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Range Description

This vole inhabits northwestern California, from Freestone, Sonoma County, north through Mendocino, Humboldt, and western Trinity counties to the South Fork of the Smith River, Del Norte County (Johnson and George 1991). There is some disagreement over the specific identity (pomo versus longicaudus) of tree voles at the northern extent of the range in northern California (see Hayes 1996).
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Physical Description

Size

Length: 21 cm

Weight: 47 grams

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Size in North America

Sexual Dimorphism: Females are larger than males.

Length:
Average: 166 mm males; 182 mm females
Range: 158-176 mm males; 170-187 mm females

Weight:
Range: 25-47 g
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Diagnostic Description

Differs from Phenacomys longicaudus in chromosomes (diploid number of 40 or 42, vs. 52 in northern range of longicaudus), smaller overall size, and certain skull and muscle characteristics (Johnson and George 1991). See key in Adam and Hayes (1998).

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Ecology

Habitat

Comments: Habitat consists of mixed evergreen forests; optimum habitat appears to be wet and mesic old-growth Douglas-fir forest, but this species also occurs in younger forests (e.g., Douglas-fir 47 years old). This vole is primarily arboreal but exhibits some terrestrial activity. It nests in trees, 2-50 m above ground; it may use old nests of birds, squirrels, or woodrats. Nests usually are in Douglas-fir trees but sometimes may be in other conifer or in Pacific madrone (Meiselman and Doyle 1996, Vrieze 1980, Zentner 1977, all as cited in Adam and Hayes 1998). Meiselman and and Doyle (1996) found that nests were most abundant in old-growth forests; the species was associated with large-diameter Douglas-fir, high percent canopy cover, high stump density, low snag density, shorter snags and logs, and lower elevation; all nests were in Douglas-fir, mostly adjacent to the trunk on the south side.

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Habitat and Ecology

Habitat and Ecology
The species' habitat consists of mixed evergreen forests; optimum habitat appears to be wet and mesic old-growth Douglas-fir forest, but this species also occurs in younger forests (e.g., Douglas-fir 47 years old). This vole is primarily arboreal but exhibits some terrestrial activity. It nests in trees, 2-50 m above ground; it may use old nests of birds, squirrels, or woodrats. Nests usually are in Douglas-fir trees but sometimes may be in other conifer or in Pacific madrone (Meiselman and Doyle 1996, Vrieze 1980; all as cited in Adam and Hayes 1998). Meiselman and Doyle (1996) found that nests were most abundant in old-growth forests; the species was associated with large-diameter Douglas-fir, high percentage canopy cover, high stump density, low snag density, shorter snags and logs, and lower elevation; all nests were in Douglas-fir, mostly adjacent to the trunk on the south side.

It breeds throughout the year. Ovulation is induced by copulation (Adam and Hayes 1998). Females may breed within 24 hours of giving birth. It sometimes exhibits delayed implantation. Gestation period is 27 to 48 days, with an average of 31 days (Hamilton 1962). Litter size usually is two, with a range of one to five (Adam and Hayes 1998). Newborns are altricial, weaned at 25 to 46 days (Hamilton 1962).

This species is thought to have very limited dispersal capability (Thomas et al. 1993). Predators include Spotted Owls (A. longicaudus made up almost 50% of prey items of Spotted Owls in Oregon), and probably other owls, Raccoons, and Fishers (Adam and Hayes 1998). This vole feeds primarily on Douglas-fir needles. It also eats needles of Grand or Lowland White Fir, Sitka Spruce, and Western Hemlock. It may eat inner bark of twigs as well (Benson and Borell 1931). Usually feeds inside or on top of its nest.

Systems
  • Terrestrial
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Migration

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Trophic Strategy

Comments: Feeds primarily on Douglas-fir needles. Also eats needles of Grand or Lowland White Fir, Sitka Spruce, and Western Hemlock. May eat inner bark of twigs as well (Benson and Borell 1931). Usually feeds inside or on top of its nest.

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

Comments: According to Gordon Gould (California Department of Game and Fish), there are currently 900 observations of nests or animals. Approximately 875 of these observations are from the mid- to late 1990s and the remainder are from the early 1990s. Observations are mapped by the California Department of Game and Fish into occupied legal sections. These data probably will result in the mapping of about 325 occupied sections in California. Gould also stated that most surveys were completed at the request of the timber industry. This species does occupy areas that are not of interest to the timber industry. As a result, there are gaps in distributional information, and many more sections may be occupied than currently indicated (Gordon Gould, pers. comm., 1998).

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Global Abundance

10,000 - 1,000,000 individuals

Comments: Total adult population size is unknown but probably exceeds 10,000. The species is relatively common in some areas, but the number of nests found can vary greatly by location and appears to be highest closer to the coast (up to several nests per acre); farther inland toward drier slopes density drops off dramatically (Gordon Gould, pers. comm., 1998). According to Brylski (1990), this species is reported to be rare to uncommon throughout the range, but the difficulty of locating nests and capturing individuals makes abundance hard to assess.

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General Ecology

Thought to have very limited dispersal capability (Thomas et al. 1993). Predators include Spotted Owls (ARBORIMUS LONGICAUDUS made up almost 50% of prey items of Spotted Owls in Oregon), and probably other owls, Raccoons, and Fishers (Adam and Hayes 1998).

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Life History and Behavior

Cyclicity

Comments: Active throughout the year.

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Reproduction

Breeds throughout the year. Ovulation induced by copulation (Adam and Hayes 1998). Females may breed within 24 hrs of giving birth. Sometimes exhibits delayed implantation. Gestation period 27 to 48 days, average 31 days (Hamilton 1962). Litter size usually is 2 (range 1-5) (Adam and Hayes 1998). Newborns are altricial, weaned at 25 to 46 days (Hamilton 1962).

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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: N3 - Vulnerable

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NatureServe Conservation Status

Rounded Global Status Rank: G3 - Vulnerable

Reasons: Restricted range along the coast of northwestern California; threatened by forest fragmentation and habitat loss.

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IUCN Red List Assessment


Red List Category
NT
Near Threatened

Red List Criteria

Version
3.1

Year Assessed
2008

Assessor/s
Blois, J. & NatureServe (Clausen, M.K., Hammerson, G. & Cannings, S.)

Reviewer/s
Amori, G. (Small Nonvolant Mammal Red List Authority) & Chanson, J. (Global Mammal Assessment Team)

Contributor/s

Justification
Listed as Near Threatened because its extent of occurrence is not much greater than 20,000 km², its range is severely fragmented and there is a continuing decline in the extent and quality of its forest habitat making it close to qualifying for Vulnerable under criterion B1.

History
  • 1996
    Data Deficient
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Global Short Term Trend: Relatively stable to decline of 30%

Comments: Information on current population trend is not available, but area of occupancy and habitat quality probably are declining (likely at less than 30% over 10 years or three generations).

Global Long Term Trend: Decline of 30-50%

Comments: Area of occupancy and abundance likely have declined compared to the historical situation. Evidence of persistence was poor in a Del Norte County population revisited in 1985 (Johnson and George 1991).

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Population

Population
The total adult population size is unknown but probably exceeds 10,000. The species is relatively common in some areas, but the number of nests found can vary greatly by location and appears to be highest closer to the coast (up to several nests per acre); farther inland toward drier slopes the density drops off dramatically (Gordon Gould pers. comm. 1998). According to Brylski (1990), this species is reported to be rare to uncommon throughout the range, but the difficulty of locating nests and capturing individuals makes abundance hard to assess.

According to Gordon Gould (California Department of Game and Fish), there are currently 900 observations of nests or animals. Approximately 875 of these observations are from the mid-to-late 1990s and the remainder are from the early 1990s. Observations are mapped by the California Department of Game and Fish into occupied legal sections. These data probably will result in the mapping of about 325 occupied sections in California. Gould also stated that most surveys were completed at the request of the timber industry. This species does occupy areas that are not of interest to the timber industry. As a result, there are gaps in distributional information, and many more sections may be occupied than currently indicated (Gordon Gould pers. comm. 1998).

Information on current population trend is not unavailable, but area of occupancy and habitat quality probably are declining (likely at less than 30% over 10 years or three generations). The area of occupancy and abundance probably have declined compared to the historical situation. Evidence of persistence was poor in a Del Norte County population revisited in 1985 (Johnson and George 1991).

Population Trend
Decreasing
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Threats

Degree of Threat: Medium

Comments: Threats include forest fragmentation and habitat loss (Maser et al. 1981; Thomas et al. 1993; Gordon Gould, pers. comm., 1998). Although the species is locally common in the foothills of mountains on the east edge of the coastal plain in Humboldt County, loss and fragmentation of habitat has been extensive everywhere within the range (Williams 1986). Timber harvest and clearing of trees for agriculture and homesites have significantly reduced available habitat and fragmented populations (Maser et al. 1981). Construction of roads and powerlines has also contributed to loss of habitat and fragmentation and isolation of populations. Furthermore, these trends are likely to continue at an accelerated pace in the future (Williams 1986).

Previously it was believed that this vole requires old-growth mesic forest and, according to Gould (1987), projections were that all old-growth forests capable of sustaining a commercial harvest in California would be cut within 25 years. Obviously such a situation would be a grave threat to the tree vole. However, recent surveys have found many nests in secondary forest and on drier inland slopes. The vast majority of recent observations come from secondary growth forest, some of which is 70-80 years old and fairly well developed (Gordon Gould, pers. comm., 1998). A 1984-1985 study conducted nest surveys in nine 20-hectare sites of young, mature, and old-growth Douglas-fir forests in northern California. A total of 79 nests were found with 39 nests occurring in old-growth forest, 22 nests in mature forest, and 18 nests in young forest (Meiselman 1987). Thus this species appears to be more adaptable and probably better able to disperse through various habitats than was previously believed.

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Major Threats
Threats include forest fragmentation and habitat loss (Maser et al. 1981; Thomas et al. 1993; Gordon Gould pers. comm. 1998). Although the species is locally common in the foothills of mountains on the east edge of the coastal plain in Humboldt County, loss and fragmentation of habitat has been extensive everywhere within the range (Williams 1986). Timber harvest and clearing of trees for agriculture and home sites have significantly reduced available habitat and fragmented populations (Maser et al. 1981). Construction of roads and power lines has also contributed to the loss of habitat and fragmentation and isolation of populations. Furthermore, these trends are likely to continue at an accelerated pace in the future (Williams 1986).

Previously it was believed that this vole requires old-growth mesic forest and, according to Gould (1987), projections were that all old-growth forests capable of sustaining a commercial harvest in California would be cut within 25 years. Obviously such a situation would be a grave threat to the tree vole. However, recent surveys have found many nests in secondary forest and on drier inland slopes. The vast majority of recent observations come from secondary growth forest, some of which is 70-80 years old and fairly well developed (Gordon Gould pers. comm., 1998). A 1984-1985 study conducted nest surveys in nine 20-hectare sites of young, mature, and old-growth Douglas-fir forests in northern California. A total of 79 nests were found with 39 nests occurring in old-growth forest, 22 nests in mature forest, and 18 nests in young forest (Meiselman 1987). Thus this species appears to be more adaptable and probably better able to disperse through various habitats than was previously believed.

This vole may have limited dispersal capabilities and thus may be vulnerable to habitat loss or fragmentation (Huff et al. 1992, cited by Adam and Hayes (1998).
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Management

Global Protection: Few to several (1-12) occurrences appropriately protected and managed

Comments: This vole occurs on a few protected sites. Less than 5% of known sites are protected (Gordon Gould, pers. comm., 1998).

The Survey and Manage program required the U.S. Forest Service to survey for certain logging-sensitive species (including the tree vole) throughout areas subject to timber sale and to provide adequate no-logging buffers if such species are found. Some vole protection was eliminated in March 2004 when the Survey and Manage provisions of the Northwest Forest Plan were withdrawn. Subsequent litigation may affect the ultimate outcome of this situation.

Needs: This species may benefit from existing/proposed conservation measures for the spotted owl (Thomas et al. 1993).

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Conservation Actions

Conservation Actions
This vole occurs on a few protected sites. Less than 5% of known sites are protected (Gordon Gould pers. comm. 1998). The Survey and Manage program required the U.S. Forest Service to survey for certain logging-sensitive species (including the tree vole) throughout areas subject to timber sale and to provide adequate no-logging buffers if such species are found. Some vole protection was eliminated in March 2004 when the Survey and Manage provisions of the Northwest Forest Plan were withdrawn. Subsequent litigation may affect the ultimate outcome of this situation.

It is necessary to determine the total extent of range and abundance of this species, and to monitor populations to determine trends and further investigate the effect of fragmentation. This species may benefit from existing/proposed conservation measures for the spotted owl (Thomas et al. 1993).
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Wikipedia

California red tree mouse

The California red tree mouse or Sonoma tree vole (Arborimus pomo) is a species of rodent in the family Cricetidae.[2] The species is found in northwest California.[1] The preferred habitat for this primarily arboreal vole is old-growth Douglas-fir forests.[1]

References[edit]

  1. ^ a b c Blois, J., Clausen, M.K., Hammerson, G. & Cannings, S. (2008). "Arborimus pomo". IUCN Red List of Threatened Species. Version 2009.2. International Union for Conservation of Nature. Retrieved 9 February 2010. 
  2. ^ Musser, G. G. and M. D. Carleton. 2005. Superfamily Muroidea. In Mammal Species of the World a Taxonomic and Geographic Reference (D. E. Wilson and D. M. Reeder eds.). Johns Hopkins University Press, Baltimore.
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Names and Taxonomy

Taxonomy

Comments: This species is represented by California populations previously recognized as Arborimus (or Phenacomys) longicaudus. Recognition as a species distinct from A. longicaudus is based on chromosome differences (diploid number of 40 or 42, vs. 52 in northern range of A. longicaudus), smaller overall size, and certain skull and muscle differences (Johnson and George 1991). Musser and Carleton (in Wilson and Reeder 1993, 2005) and Baker et al. (2003) accepted A. pomo as a species distinct from A. longicaudus.

There is no consensus on the proper generic allocation for this species. It was placed in the genus Arborimus by Johnson and George (1991), Musser and Carleton (in Wilson and Reeder 1993, 2005), Hayes (1996), Adam and Hayes (1998), and Baker et al. (2003); included in the genus Phenacomys by Carleton and Musser (1984), Repenning and Grady (1988), and Verts and Carraway (1998). Bellinger et al. (2005) noted that recognition of Arborimus as a distinct genus is subject to interpretation of data.

MtDNA data (Bellinger et al. 2005) indicate species-level differences among red tree vole (Arborimus longicaudus or Phenacomys longicaudus), Sonoma tree vole (A. pomo or P. pomo), white-footed vole (A. albipes or P. albipes), and western heather vole (P. intermedius) but no clear difference between the two Oregon subspecies of red tree voles (longicaudus and silvicola). These data further indicate a close relationship between tree voles and A. albipes or P. albipes, validating inclusion of albipes in Arborimus. Bellinger et al. (2005) did not find that P. intermedius clustered with Microtus.

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