Conservation and Ecology of the Salt Marsh Harvest Mouse

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Conservation and ecology of the Salt Marsh Harvest Mouse

The salt marsh han"cst mouse is en tide marshcs in the San Francisco Bay area ha,·c ~~ demie to the salt marsh areas sur been fillcd or othcrwise highly modified Oones and rounding San Francisco Bay and its StOkes Ct al. 1979, Goals Project 1999). Most diked tributaries (Shellhammer 1982, 1989). Two sub marshes occur in the Suisun Bay where a number of ( species of the mouse currently are recognized: R. small. distinct populalions of the northern sub r. (ol'iI,tnJdJ occurs in the southern San Francisco species exiSl (ilan'cy and Stanlcy Associates 1980). Bay region; whereas, .K [. ha/;corlrJ occurs in the northern region of the bay (Shellhammer [982). The mOllse was dccl:"trcd an cn~ dangercd species in 1970 by the U.S. Department of the Interior and in 1971 by Iile California De partment of Fish and Game (Shell hammer 1982). The principal rea son for listing the salt marsh har "cst mouse was habitat loss (LI.S. Fish and \X'ildlifc Sen,jce 1984). Primary habiHlt for sah marsh har "CSI mice was described by Shell hammer ct al. (1982) as pickleweed dominated areas with escape cO\'er ;======, from inundation during high tides. 0'1 I>ISTI'LUSlIl'ti (II \R KTI Rl:llTH. Of Till'S \l.T M "btl H \R\"EST ,\bout 80 percent of Ihe original- ;\IOLSr 1~' C\l'1 '\TtRI. \5 HIDI '11-1) 1:1\ THIS Rr\CTIO' TO BFI'(, CI.OSl.l.\ 1'\'11'11), ly estimated 4-4 km2 of historical L ---' 'lJuc.ts Qinfimrled

V\LLLY BA\ HABITATS

Description The salt marsh harvest mouse is a small new world mouse (Family Cn"utidot, Order RJJdmlio). Unlike house mice (.HitS mIlJrHlus). which are gen erally gra}'. salt marsh han-cst mice are orange • brown. They weigh only 8 to 14 g and their tOlal •

length ranges from 118 [Q 175 mm (SbcHhammcr 2000). Their tail tends to be at least, or longer,

than t heir bodies. \X'hen compared with the western han'cst

mouse, the salt marsh han"cst mouse tends 10 han darker ears and dorsal areas; thicker, less

pointed, and more uniform (not bicolored) tails; San Franel o. and often darker bellies. l\lost northern sub

species have whitish \'Cnlcrs with aT-shaped • Hayward darker orange pattern extending across the chest and to the base of the tail. The cinn:tmon or:tngc ( or rufous color of the ,·cnter of [he southern sub species accounts for the Latin n:tme, rnl'it'tnlriJ, or

red-bellied mouse; howe,"er, this is actuaUy :l. mis nomer for the species (Fish and \'\'i1dlife Sen'ice 1984). Differentiating between salt marsh and western harvest mice in the field is difficult. Identifying GEOGRAPIltC DJSTRIKL'TlO' OJ, RE/TlfRODO.'TO.\fH RAJ '/1'1':." FR.\'r:I~CO characteristics include the genernl body color; nus J'o< Tllr SA' B\y RI'GJO' 01' CAJ.lIOR'I\. O .... LY PR .....r IP..I. POPl'L\TIO'S .\RI' 'OTlcD. 5QL\RI,s J'DI color of ,-entral hairs; thickness and shape of the C\Tl:. R. R"H -II r.YllUJ IL-lUCOE7Ef \\,D OPI , CIRCLES I'DI tip of the tail; tail/body ratio; and behavior (Fisler C...TE R. It It''I'lI'EXTlUJ. 1965, Shellhammer 1981). distribution (Fish 2nd Wildlife Service 1984). Distribution The northern subspecies of thc salt m2rsh h:trvest Salt marsh harvest mice evolved with the creation mouse occurs from the Gallinas Creek area on the of San Francisco Bay some 8,000 to 25,000 ycars ago. t-.larin peninsula across the San Pablo Bay through Fisler (1965) suggests that these mice were found in the Carquinez Strait into the Suisun ~larsh and the most of thc marshes throughout San Frnncisco Bay. northern Contra Costa County coast. The southern The wetlands and marshes of the original Sacrnmen subspecies has a distinct distribution, There is a to-San Joaquin Deha werc probably too fresh to sup small population in Marin County at Cone Madera pon mice, and hcnce, the Collins"ille-Antioch area and a small population near Point San Pedro in probably was, and still is, the e:l.SfCrn limit of their northwestcrn Contra Costa County.

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The remainder of the southern subspecies occurs Therefore, Bias (1994) suggests thai Ihe breeding in the band of salt m:l.fsh around the San Francisco season of salt marsh harvest mice, based upon the Ba~' from Belmont, San Mateo County, around to female cycle, is from September to December in the

the t cwark area of Alameda County (SheUhammcr San Pablo Bar area. The breeding season for the 1982). southern subspecies is apparently ~by through No vember (Fisler 1965). Fisler (1965) also noted that Ecology the northern subspecies had an average litter size of Population - The greatest consistent popula 3.7 to 3.9; while the southern subspecies had an av tions of salt marsh harvest mice occur in the rela erage litter size of 4.0. th'ely large marshes along the eastern edge of San Gcissel et al. (1988) reported greatest salt mush Pablo Bay and within former dredge spoil disposal haryest mouse recruilment in the south San Fran ponds at Ihe former Mare Island Na'-al Shipyard cisco l3ay region to be from June and July. Fisler (Bias 1994, Duke el aJ. 1995); most of which will be (19-1) reported Ihat recruitment in the soulhern included in the San Pablo L:nit of the San Francisco subspecies occurs more e"enlr through the year Bar National \'('i1dlife Refuge (Shellhammer 2000). Ihan the northern subspecies. Perhaps breeding sea Salt marsh han-esl mice ha,-e disappeared from sons for the IWO subspecies occur at different times ( many marshes and are present in re1ati,-ely low num of the year. Fisler (19-1) reported grealest recruit bers in most 01 hers around San Francisco Bay and ment of ju,-cnile sah marsh han'est mice from Oc Suisun Marsh (Shellhammer 2000). Population esti tober to December. Fisler's (1971) results were sim mates within a ye:l.r indicate that the least numbers ilar to l3ias (1994), in that most (>5 percent) juve of salt marsh han'est mice occur during September nile salt marsh harvest mice in the San Pablo Bay and October and the greatesl during June (Bias area occurred in the populalion from September to [994). Funher, telemetrr results from Bias and November. I\lorrison (1999) suggested that the gre:l.tesl dis tances traveled occurred during June. Home range - This species probably is nOl ter ritorial (Fish and \'\'ildlife Service 1996). There have Demography - Fisler (1971) reponed a pre been few studies of home range and then only in ponderance of pregnant female salt marsh harvest "ery narrow, elongated marshes (Fish and \'\'ildlifc mice (36 percent) during November and December Sen'ice 1996). Geissel el al. (1988) reported home , and suggested that the breeding season was from range sizes for four adult male ~. = 1,550 m2) and 4 .\Iarch [hrough Nm·ember. Bias (1994) sho\\'ed thai aduh female _' = 1,300 m2) salt marsh han'est mice of female salt marsh harvest mice caprured from in the south San Francisco l3ay area based upon Ii'-e \988 to 1992 in San Pablo Bal' mOSI (>30 percent) trap data. Bias and Morrison (1999) showed thai were pregnant during September and OClObcr. home range estimates for sa.lt marsh han·cst mice Also, of the male sah marsh han'est mice capwred, were considerably larger (138-164 percent) than more than half were reproductively anive from Geissel el al.'s (1988) estimates, hO\'\'e"er direct com June to September. parisons were not valid because of the different tech-

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V \ LL E , • B\, HABITATS

nI'Iues used to eSlim:ltC home range size. Bias and Morrison (1999) showed tl1:11 mean distances moved between observations and home range areas for males

(ended 10 be gre:ncr than fe males. Geisscl Ct 31. (1988) rc paned similar findings, in that adult male sail marsh harvest mice ffim'cd further than females. Bias and l\lorrison (1999) showed also Ihal moyemcm pal terns of salt marsh han'cst mice revealed that the mice readily r======~~~~~~~~~~~~~~~~~~~~~~ cross barren dikes, roads, and PKh:Ll\\I'I,D I~ I\lPORT.\'T TO Till" SAI.T i\!\RSII H\R\T~T ;\IOl-~I_" SIIOW,

tidal channels (>2 m wide)_ For In RE ., (H \lU(Tl,RI,STIC I \LL (Ol.ORS. PIC"U,WEED \IIXI I) WITII I,\T III,' \'[),1..... \1.1 III nH \PPL,RII) TO 81,: 1,\HlRED 8Y Till .sPE(:Il~. example. several mice regularly L-,- -;-:-,-_;-_,-:-,- ,-:-_---:_...,- -.J crossed tide channels or roads, Another mouse would be found within grasslands only when there tra\'clecl a straight-line distance of about 800 m. \\'as adequate co\'er. primarilr from April to August.

These results concur with Gcisscl Ct al.'s (1988) ob Rcsuhs from detailed analyzes of li"e trap and

servations that barren areas afC not effective barri telemetrr data of habitat usc by salt marsh harvest

ers [Q mO\'crnem berween populations of salt marsh mice fully suPPOrt these findings (Bias 1994), Re harvest mice as suggested by Fisler (1965) and sults from Ihese analyzes showed that \'egetation Shellhammer (1977). density and height; cover of picklcweed. fat hen, and other forbs; and co,"er by gr3SS and grass liner Habitat use - Salt marsh han'cst mice appar were Important components of salt marsh han'est ently arc dependent upon thick plant cover (Fisler mouse habitat. 1965. Shellhammer et al. 1982). Primary habitat for Vegetation characteriSlics at all S:l.lt marsh han'est salt marsh harvest mice was described by Shellham mice telemctry locations support fisler's (1965) and mer Ct al. (1982) as picklcwecd with escape co,"er Shellhammer et al.'s (1982) deSCription of primary from inundation during high tides, The value of h:l.hilat (Bias 1994). pickleweed increased with height, densi~. and the Fisler (1965) reported an apparcnt mo,'ement of degree of imermixing with fat hen 2nd 2lkali heath salt marsh han'est mice to higher marshes in wimer (Frrmktflia grtlfldijo/ia) (Shellhammer et al. 1982), and proposed th:l.t this was a reaction to extremely Further, Fisler (1965) suggested that harvest mice high tides in December and January. Shcllhammer

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(1982) concurred with Fiskr's (1965) observ:uions Management Implications and reponed the importance of an upper zone of The Fish and \,\'ildlife Service (1984) enumerated non-submerged plantS that can act as refugia for sah the principal reasons for the decline of the salt marsh marsh harvest mice during the highest tides. Thus, harvest mOllse as: the future of the salt marsh harvest mouse will de (I) habitat loss; pend upon management programs for both zones (2) fragmentation of the remaining marshes; (Shellhammer 1982). (3) widespread loss of the high marsh zone as a rc~ There ha\'c been few studies that examined salt suIt of backfilling; marsh harvest mouse habitat usc differences either (4) land subsidence; and berween sexes or among seasons. Bias (1994) bas (5) vegetational change. shown that male and female salt marsh harvest mice j\lost remaining marshes are affected by more than used different habitats during the summer, primary one of these factors. Reccmh', Shellhammer (2000) breeding, and fall seasons (i.e., July through Decem detailed current, more-specific threats and areas re ber). quiring more detailed study to properly manage salt However, males and females tended to usc similnr marsh harvest mice in the long term. These threats habitats during the winter, spring, post-breeding, and questions include: :lOd pre~breeding seasons (i.e., December through (1) Little is known about the population genetics July). of tllis species if it is to be properly managed o\'er the long term. Food habits - Salt marsh harvest mice are large (2) It is not known how much upland edge consti ly vegetarians, cating primarily green vegetation and tutes enough of an upland buffer to protect popula grasses, in addition 10 seeds. They can drink water tions from alien predarors (feral cats) and human dis ranging from fresh to moderately salinc to seawater turbance. (Fisler 1965). Little else is known of the food habits (3) The impact of the introduced red fox (I ~f(lpfS of the salt marsh harvcst mouse, and little work has mlpn) is not known. Further, very little is known re been done since that of Fisler (1963,1965). gatding the effecrs of predators on the salt marsh harvest mouse. Behavior - Salt marsh han"est mice are good (4) Little is known about the interactions of \'ari swimmers. Their beha\'ior is calm, so much so thaI ous species of rodents in the salt marsh and diked calm behavior is a criterion used to help identify it marsh species community. from the very similar western harvcst mousc (Rd· (5) Little is known about the impact of exotic throdolltollJYs megll/otis) (Shellhammer 2000). Neither weeds, especially pepper grass (Leprdi,,", /tJtifo/i/lJJl), on subspecies burrows, rhe northcrn subspecies builds the salt matsh harvest mouse. ball-like nests; whcreas, the southern subspecies docs (6) Shellhammer (2000) infers from (Bias 1994, not (Shellhammer 1982). Both subspecies arc noc~ and Bias and j\[orrison 1993) that there is a possibil turnal, becoming acti,"c around sunset and inactive ity that younger pickleweed salt marshes arc marc around sunrise (Fisler 1965). productive (han older ones for the salt marsh harvest

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mouse. Other threats include those th:u may occur oped and implemented on all marshes. These plans from the usc and application of pesticides and effect may include remO"a! of exotic vegetation; planting of pollution ancl contamlnalHs (Bias 1994). native plant species in the upper marsh; restricting land fiIHng, plowing, mowing and burning; minimiz Recovery ing or preventing freshwater flushing; limiting human

The Fish and \'{'ildJife Sen'ice is preparing a new access 10 upper marsh areas; diking in some areas; endangered species fcconry plan that will include re restoring tidal aCtion; and eliminating or reducing co\-cry actions 10 help the salt m:ush han-est mouse. pesticides (e.g., for mosquito control or agriculture) This plan entitled, JVrol-'eIJ Plall for Tidal Marsh Ero.rys and pollution. Itlm of em/rill (Jlltl j\'ortMrn California, will revise and 3. Unprolecled marshes and essential marshes expand the existing fCCOnrr plan (Fish :lnd \X'ildlife need to be secured and managed to allow the reStor3 Service 1984) for the salt marsh harvest mouse and tion, enhancement, or creation of habitat rich in California clapper rai1. pickleweed. llabitat may be secured and protected The primary objective of the recovery plan (Fish from development through land acquisition, cooper and \'('ildl..ifc Service 1984) is: ati"e agreements, or other means. (1) to secure and manage 3,900 hectares of essen 4. Upper ponions of marshes must be restored to tial habitat under go'-ernmem jurisdictions; proyide refugia during high tides and to prO"ide nest

(2) to secure and manage 3,200 hectares of habitat ing habitat In marshes that ha\-c subsided and "egeta that is mostly pri\'ately owned; and tion changed. In some instances this may invoke (3) to restore or enhance 7,000 hectares of historic crcaung islands or peninsulas of high ground for habitat. The completion of the foregoing would refugia. allow the StatuS of the northern subspecies of mouse 5. Biological research on sewage effluents, poilu to be upgraded to "threatened" with consideration lantS, nood control measures, salinity, mosquitO for deiisting, and the southern subspecies of mouse abatement, rise in sea level, reduced sedimentation, and the ra.il population to be upgraded to "threat marsh erosion, and marsh accretion is needed to pro ened". Delisting of the rail and southern subspecies "ide information essential to recO"ery effofts. of mouse may be possible following completion of 6. Reeslablish populationc; al selected locations the above habitat, plus restOration or enhancement through translocation of wild indi,'iduals. of a currently estimated at about 3,000 hectares of 7. De,'c1opment and implementation of a program additional habitat. Specifically the current recO\'ery for conservation education. plan (Fish and \'\'ildlife Service 1984) outlines the fol These aClions coupled with Ihe sound application lowing actions arc nceded to meet the recovery crite of management principals and proper application of ria listed above: tidal marsh restoration efforts, such as many of lhe 1. Existing marshes must be protected, and efforts currently being implemented Ihroughollt lhe marshes should be interconnected or combined in San Francisco Bay, should a~sure reCO\'ery and delist

order 10 creale maximum populations. ing of the salt marsh harvest mouse from the endan·

2. Ilabitat management plans need 10 be de,'c1- gered species list.

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Literature Cited marsh. J. ~[nmmal. 69(4):696?703. Bias, i\l.i\. and t\1.L. Morrison. 1993. f'inal rc- pon: sail marsh han'csl mouse on i\larc Island Goals project. 2000. Baylands ecosystem habi Naval Shipyard, 1989-1992. Unpublished report to t:\[ goals. U.S. Environmemal Protection Agency, Nat. Res. i\1:lnage. Branch, Western Oiv., Naval Fa San Francisco, CA/San Francisco Ba)' Regional cilities Engineering Command, San Bruno, Ct\. \'(Iater Quality Control Board, Oakland, CA 209pp. 223pp. Harvey and Stanley Assoc. 1980. Status of the ___' 1994. Ecology of the salt marsh harvest salt marsh harvest mouse (ReithrodolHomys ra mouse in San Pablo Bay. Ph.D. Dissen., Uni\'. Cal vi"entris) in Suisun !\larsh. Prepared for Water and ifornia, Berkeley, CA. 243pp. Power Res. Ser., Sacramemo, Calif. 52pp.

___ :'tnd j\1.L. i\lorrison. 1999. i\lovemcnts Jones and Srokes Assoc., Harvey and Stanley and home range of salt marsh harvest mice. The Assoc., and John Blayney Assoc. 1979. Protection Southwestern Naturalist 44(3):348-353. and resroration of San Francisco Bay fish and wildlife habitat. Volume I. U.S. Fish and Wildlife ( Duke, R.R., 1-1.5. Shellhammer, R.I\. Hopkins, E. Service and California Department of Fish and Steinberg, and G. Rankin. 1995. Marc Island Na\'al Game, Sacramento, Calif. Shipyard salt marsh harvest mouse 1994 trapping surveys. Prepared for Dames and I\loore. Tuscon, Shellhammer, 1-1. S. 1977. Of mice and marsh AZ by H.T. Harvey and Assoc., AI"iso, CA. Project es. San Jose SlUdies, San Jose State Univ., San Jose, 921-01. California 3:23?35.

Fisler, G. F. 1963. Effects of slat water on food 1982. Reidtrodontomys raviventris. and water consumption and weight of harvest I\lammalian species. 169: 1-3. mIce. Ecology 44:604-608. . 1984 Idenllficatlon of salt marsh harvest 1965. Adaptations and speciation In mice, Reithrodontomys ra"iventris, in the field and harvest mice of the San Francisco Bay. Univ. of with cranial characteristics. Calif. Fish and Game. Calif. Publ. Zool. 77:1?108. 70,113-120. 1971. Age structure and sex ratio in populations of Reithrodonromys. J. Mammal. 1989. Salt marsh harvest mice, urban 52:653?662. development, and rising sea levels. Conserv. BioI. 3:59-65. Geissel, W., H. Shellhammer, and H. T. Harvey. 1988. The ecology of the salt?marsh han'est 2000. Salt marsh hanest mOllse. 219 mouse (Reithrodontomys ravivemris) in a diked sail 228pp. In: Goals project. 2000. Barlands ecosys-

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rcm species find community profiles: life histories and environmemal rccluiremems of key plants, fish About the Author and wildlife. Prcpared by the San Francisco Bay Dr. Mike Bias received his Ph.D. from the Area \'\/etlancls Ecosysfem Goals Project. P.R. University of Califomi a at Berkeley in 1994. He Olofson, ed. San Francisco Bay Regional Water worked on the ecology of the Salt Marsh Harvest Quality Control BOflrd, Oakland, CA. Mouse since 1988. From 1994 to 1999 he was

U.S. Fish and \Xhldlife Service. 1984. Salt marsh har the Regional Biologist for Ducks Unlimited, Inc. veST mouse and California clapper rail reco\'cry plan. in the Central Valley ofCaliforni a a San Francis Portland, Oregon. 141 PI" co Bay Estuary. Dr. Bias continues to conduct re search evaluating wetland restoration and the __" 1996. Salt marsh harvest mouse. In: En Salt Marsh Harvest MOllse. dangered species information system. 331'1"

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Ducks Unlimitcd, Inc., \,'cstern Regional Office 3074 Gold Canal Dn\"e Rancho Cordova, C\ 95670-6116 Telephone 916-852-2lXJO FAX 916-852-22(x) Ducks Unlimltec:l, Inc. on me Internct at Innl:dllrks.org

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