Recovery Plan for the Point Arena Mountain Beaver

80 Pages·1999·4.57 MB·English

Recovery Plan for the
Point Arena Mountain Beaver
Aplodontia ru fa nig ra (Ra finesque)
POINT ARENA
MOUNTAIN BEAVER
Aplodontia ru/a nigra (Rafinesque)
RECOVERY PLAN
Preparedby’
Dale T. Steele
and
Laurie Litman
for
Region I
U.S. Fish and Wildlife Service
Portland, Oregon
Approved:
Reg 1 D e .S. Fish and Wildlife Service
Date:
Disclaimer
Recovery plans delineate reasonable actions which are believed to be required to
recover and,’or protect listed species. Plans are published by theU.S. Fish and
Wildlife Service, sometimes prepared with the assistanceofrecovery teams,
contractors. State agencies, and others. Objectives will beattained and any
necessary funds madeavailable subject to budgetaryand other constraints
affecting the parties involved, as xvell as the need to address other priorities.
Costs indicated for task implementation and/or time for achievement ofrecovery
are only estimates and subject to change. Recovery plans do not necessarily
represent the views northe official positionsor approval ofany individuals or
agencies involved inthe plan formulation. other than the U.S. Fish and Wildlife
Service. They represent the official position ofthc U.S. Fishand Wildlife Service
wily afterthey havebeen signed by the Regional Directoror Director as
approved. Approved recovery plans are subjectto modification as dictated by
new findings, changes in species status. and thecompletion ofrecoverytasks.
Literature Citation shouldread as follows:
U.S. Fish and Wildlife Service. 1998. PointArena MountainBeaver (Aplodontia
ru/a nigra (Rafinesque)) Recovery Plan. Region 1, Portland, OR. 71 pp.
Additional copiesmay be purchased from:
Fish andWildlife Reference Service
5430 Grosvenor Lane, Suite 110
Bethesda, Maryland 20814
301/492-3421 or 1-800-582-3421
The fee for the Plan varies depending on thenumber ofpages ofthe Plan.
Acknowlcdgmcnts
Thefollowing individuals contributed significant information/assistance during
recovery planpreparation:
Dan Campbell
Jim Dines
Gary Fellers
Kim Fiffs
Sarah Flowers
Gordon Gould
Rickye Heffner
Mike Horton
Kevin Joe
CarylaLarson
Alan Levine
Darlene McGriff
Richard Meredith
Phil Northen
Renee Pasquinelli
BertPfeiffer
Ron Schlorff
Brad Valentine
Alison Willy
TedWooster
Special acknowledgement forthe pioneering Aplodontiarufa nigraresearch by C.
Camp and E. Pfeiffer.
Thecover drawing is used courtesy ofthe California WildlifeHabitat
Relationships Program, California DepartmentofFishand Game, Wildlife
Management Division from: D.C. Zeiner, W.F. Laudenslayer, Jr., K.E. Mayer,
and M. White, eds. 1990. California’s Wildlife, Vol. III, Mammals. California
Statewide Wildlife Habitat Relationships System. State ofCalifornia, The
Resources Agency, DepartmentofFishand Game, Sacramento, California.
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Executive Summary
CurrentSpeciesStatus: The Point Arenamountain beaver (4plodontia rufa
nigra,) isa federally listedendangered subspecies. This subspecies ofmountain
beaveris only known from a small areaofcoastal Mendocino County, California,
where26 apparently separate populations have beenfound, with an estimated 200
to 500 animals total. Potential threats to thehabitat ofthe species include
elimination or degradation from land development, grazing, timberharvest, and
invasion by alien plant species. Directthreats to the subspecies may include
predation by household pets and feral animals,poisoning, genetic isolationand
genetic drift, and human caused disturbance. Basic biological data are lacking to
determinethe level ofvulnerability ofthe mountain beaverto eachofthese
factors.
Habitat Requirements andLimiting Factors: A. r. nigra requires acool moist
environment. It lives in underground burrow systems under dense standsof
perennial vegetation where soil conditions allow foreasy excavation.
Recovery Objective: The ultimate objectiveofthis planis to delist the Point
Arenamountain beaver, however, criteriafor downlisting to threatened are also
established.
Recovery Criteria: The species will be considered for downlisting when:
1. At least 16 populations are protected from human-caused
disturbance in perpetuity. Eachpopulation shall contain at least 20
hectares (49 acres)ofsuitable habitat ofwhich at least 10 hectares
(25 acres) are occupiedhabitat.
2. Thesepopulations shall have amean density ofatleast 4 Point
Arena mountainbeavers per hectare (1.6 per acre)ofoccupied
habitat, unless newdata show that a lowerdensity is healthy and
stable.
3. All 16 populations are stable (i.e., no morethan a25 percent
change in estimatedpopulation size from highest to lowest value)
or increasing for aperiod ofat least 10 years (following attainment
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ofcriterion #1),as documented through establishment and
implementation ofa scientifically acceptable population
monitoring program.
4. Theamount ofadditional habitat needed for population
interconnectivity, travel, and dispersal habitathas been determined.
5. Sufficient information isavailable to permitadaptive management,
and any managementactions necessaryto ensure the continued
success ofthese populations (in criterion #1) have beenfully
implemented.
The species will be considered for delistingwhen:
1. Thirty populations are protected from disturbance in perpetuity.
Each population shall containat least20 hectares (49 acres) of
suitable habitat ofwhich at least 10 hectares (25 acres) are
occupiedhabitat.
2. These populations shall havea meandensity ofat least 4 Point
Arenamountainbeavers per hectare (1.6per acre)ofoccupied
habitat, unlessnew data showthat a lowerdensity is healthyand
stable.
3. All 30 populations are stable (i.e., no more thana25 percent
change in estimatedpopulation size from highest to lowestvalue)
orincreasing for aperiod ofat least 15 years (following attainment
ofcriterion #1), asdocumented through establishment and
implementation ofa scientificallyacceptable population
monitoring program.
4. Additionalhabitat needed forpopulation interconnectivity, travel,
and dispersal habitat has beenprotected and is being managed
appropriately.
5. Adaptive management prescriptions have beendetermined and
implemented forall populations.
Actions Needed:
1. Protect known populations.
2. Protect suitable habitat, buffers, and corridors.
3. Developmanagement plansand guidelines.
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4. Gather biological and ecological data necessary for conservation
ofthe subspecies.
zi. Determinefeasibility of,and need for, relocation.
6. Monitor existing populations and survey for new ones.
7. Establish an outreach program.
Estimated CostofRecovery: $1,047.000±.The total cost ofthis recoveryeffort
could be higherthan this figure. The costsfor several tasks neededfor recovery
have vet to be determined.
Date ofRecovery: Downlisting could be initiated in 2015 and delisting by 2025.
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Table ofContents
I. Introduction 1
.
A. Description 1
B. GeographicalDistribution 2
C. Habitat
D. Life History/Biology/Ecology 12
Burrows 12
Population Density 14
Nest 15
Burrow Commumtv 15
Cleanliness 16
Foraging 17
Activity 18
Thermoregulation 19
Osmoregulation 20
Behavior 20
Senses 21
Demographics
__
Fragility 24
Pest Control 25
F. Reasons for Listing and Threats to Survival 26
..
F. Conservation Measures 31
II. Recovery 34
A. Objective and Criteria 34
Downlisting criteria 34
Delisting criteria 35
1-3. Stepdown Narrative 36
C. Literature Cited
__
D. Personal Communications 60
F. ,n kct’crenccs 61
/0!
Iii.
... 1~ienwntation Schedule
_
IV. Appendix A: Summary ofComments 67
List ofFigures
Figure 1. Distribution ofknownAplodoutia rufa subspecies
. . .
Figure 2. Distribution ofknown Point Arena mountainbeaver populations 8
List ofTables
Table 1. Museum specimens ofthe Point Arena mountain beaver 4
Table 2. Known populations ofthe Point Arenamountain beaver 6
Table 3. Chronologyofresearch on the Point Arena mountain beaver 13
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I. Introduction
A. DESCRIPTION
The Point Arena mountain beaver (Aplodonhia ru/a nigra,) was listed as a federally
endangered species by the U.S. Fish and Wildlife Service on December 12, 1991
(50 FR 64716). It is also listed asa highest priority “Species ofSpecial Concern”
by the State ofCalifornia (Williams 1986). This subspecies has been given a
recoverypriority number of3 given that it is facedwith a highdegreeofthreat
and has a high recovery potential.
The firstpublished account ofmountain beaver. Aplodontia ru/a(Rafinesque),
comes from the journals ofLewisand Clarkin 1805 (Godin 1964). The Point
Arena subspecies was originally describedby Taylor (1914)as a separate species,
.4plodon;ianigra, because ofits unique colorand certain anatomical features. It
was later revised to subspecies status.Aplodonhia rufa nigra, due to overlap of
characteristics with other subspecies and lackofrepresentative specimens (Taylor
1918). This classification has been upheld through severalrevisions (Dalquest
and Scheffer 1945. Hall and Kelson 1959, Hall 1981). A considerable degreeof
geographical and individual variationexists within subspecies ofAplodontia
(Dalquest and Scheffer 1945). Isolation is probably’a major factor inthe
speciation(ic., the processofdifferentiation into species and subspecies) ofthe
genus (Finley 1941).
Themountain beaver has been comparedto an overgrown pocket gopher(Ingles
1965) and a muskrat without a tail(Racy 19? Its body is stout, compact and
cylindrical. Anaverage adult measures slightly more than 30.5 centimeters (1
foot) in length and weighs0.8 tol .8 kilograms (2 to 4 pounds) (Feldhamer and
Rochelle 1982). The skull is relatively broad,massive, laterally compressed. and
notable forits flatupper surfacc and lack ofpostorbital processes (spurofbone
above the eve socket) (Hall 1981). Long,stiffwhiskers (vibrissae) are present on
the nose. and guard hairs are plentiful in the fur. A little patch ofwhite hair
occurs at the base ofeach ear. The eves and ears are quite small. Limbs are short,
the fore and hind limbs of about equal length. The forefeet have functionally
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opposedthumbs, and all digits have long,curved claws. Adistinctive feature of
its external anatomy is its cylindrical stump ofatail.
Severalcharacteristics distinguish the PointArena mountainbeaver from other
subspecies. Themost obvious is its unique black coloration. The outline ofthe
nasalsis also distinctive, asare some cranial measurements (Taylor 1914). A. r.
nigra is also the smallestoftheCalifornian subspecies.
The mountainbeaver, also known as sewellel,boomer, and many othernames, is
notclosely related to truebeavers (Castor). Aplodontia are consideredto be the
oldest group ofliving rodents, being the sole extant member ofthesuperfamily
Aplodontoidea, whichhas been almost morphologically unchanged in the fossil
record sincethe Miocene (Simpson 1945). This “living fossil” is thoughtto be
ancestral to the squirrel family (Shotwell 1958).
B. GEOGRAPHICAL DISTRIBUTION
The PointArena mountain beaver isknown only from its type locality, an areaof
about 62 square kilometers (24 squaremiles), entirely in western Mendocino
County (Camp 1918). The seven subspecies ofmountainbeaver are found in
cool, moistclimates along the Pacific Coast ofNorth America, from southern
British Columbiato Point Reyes,California and east to the Cascade and Sierra
Nevada Ranges (Scheffer 1929)(Figure 1). Four subspecies are found along the
northern coastofCalifornia theHumboldt mountain beaver (Aplodontia rufa
humboldtiana), the PointReyes mountain beaver (A. r. phaca), the Point Arena
mountain beaver (A. r. nigra), and the Pacific mountainbeaver ~JAr..pac~fica,,).
ThePoint Arenaand Point Reyes subspecies are isolatedby considerable
distances (Steele 1986). The Point Arena mountainbeaver isabout 130
kilometers (80 miles) south ofthe Humboldt mountain beaver, and the Point
Reyes mountain beaver is 100kilometers (60 miles) south ofthe Point Arena
mountain beaver. The lengthoftime these populations have been isolated is not
known. Also, note that theSierra Nevada mountain beaveris not endemic to
California, as ithas been collected within theNevadaportion ofthe TahoeBasin.
Historical records ofA. r. nigra are scarce (Table 1). Camp (1918) reported that
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