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<br />_ Implication of the Effecta of Cloud Seeding on Small
<br />Mammals
<br />
<br />Whether cloud seeding is good or bad is a value judg-
<br />ment that lnvolves a compLeX system. Slnce deer mice
<br />showed the greatest relationship with ~nowpack. I
<br />will use this apecies as an example of the complexity.
<br />Deer mice primarily eat .eeds during the winter
<br />(Johnson 1962~ Vaughan 1974). Although deer mice occur
<br />mainly on the south aspects. they do invade Dorth
<br />. aspects when population densities are high; where.
<br />because of their seed eating babits. tbey could po-
<br />tentially interfere with natural reforestation of
<br />conifers. ~eavy sDowpsck results in a reduction of
<br />deer mice. so no deer mice are on the north 8sDects
<br />and foresters might then consider cloud seed in ood.
<br />eer m ee ee pr mari y on nseets during the summer.
<br />and vith the bulk of the deer..1IlOuse population on the
<br />south aspects. there could be a reduct10n at ner01-
<br />vorous insecta and thus .ore torage vou~d rema1.n for ;
<br />elk and catt~e. Heavy sDowpacK.TeauLts 1n a.reQuct10n
<br />of deer mice. so'rancher_ and hunter. could consider
<br />cloud seeding .bad. " Tb1_ ',~l!I:~~.p~..ented ,two ,:
<br />.1dea to th~ .1~..~ o.f c:l~u~. ~~~~~.,~":.:.!.;~~~o-:, ~~ .
<br />deer ~ee. yec:eY8n this.i_ ...~.,lifleatlon bec.ua.
<br />ther.' are many. other interaction.. tbat could be con-.
<br />sidered befor.'maklDg jUdgement.. When considering
<br />.11 tha apeclu ,~f.,._ll', .........h.. ;the .y~t~ becomes
<br />ev...-.or.e co-.plex,~:,:'Kaa7'.1Ilt~~t;~ .were oat atudiec!
<br />dunGS the cour..;'of .tld. 'proj,ect'.\: Decle1on. aad.
<br />solely 00 the~ruult. of thia'project could be errone-
<br />ous. becaua. of .tbe llm1ced .cop. of , this project.
<br />, :. ';. " .. ~ '. . '~', ,;'. ' .. ' . -
<br />
<br />Extrapolation of results in ~ atudy to otber ~re.s
<br />of the montane ecosystem iUgbt 'DOt be .ppropriate.
<br />Vaughan (1969) studied lIOotR.e ...11. _-.18 $,0',
<br />northern Colorado. .B1s data .bow dilferent. popula.tioQ;
<br />trends in relation to snovpad:, although be ,d~~ .DOt
<br />quantif)' his snowpack data. ' '
<br />
<br />Summary
<br />
<br />Substantial home range data were obtained on deer mice
<br />during the snow free period of the year. During the
<br />firs~ 3 months after 8nowmelt. deer ~use bome range
<br />size vas highly correlated (r--a.90) with population
<br />size. Hypothesis A (Summertime bome range will be
<br />unaffected by snovfall) would be accepted for deer
<br />mice, because of the relationship of home range ,to
<br />population size. Snowpack only has an i~d1rect effect
<br />on home range through population aize. Data 'were'
<br />insufficient to,make concluslo~a on Bypotheals.A.for
<br />the 'other four speeie.. but I ~ect the hypotheSis
<br />yould be accepted if sufficient-data .were available.
<br />
<br />Hypothesis B (Increased .navfall viII increJ.e mortality
<br />rates in the winter of occurrence and the summer follow-
<br />ing) would not be.accepted for .ny apeeies. because
<br />of its two parts. Tbere are data to snSYer the ftrst
<br />part. but the phrase Itand the eWlllHr follov:1ng" make.
<br />the hypothesis too broad to be testable. because
<br />summer and winter mortality appear to be affected by
<br />diUerent variables.
<br />
<br />Density estimates for five species of small mammals
<br />'Were obtained during eech live trapping period. Sample
<br />sizes varied greatly, with deer,a1ce providing the
<br />best data and long-tailed voles providing tbe least
<br />reliable data. Deer.uouse population size had a
<br />strong negative relationShip with soowpack, and chip-
<br />munk population 8ize had a weak negative relationsbip
<br />with snowpack. The other three species reacted to
<br />variables other than sDowpack. thus obscurtns any
<br />relationships with snoYpack. Annual variability in
<br />snowpack is probably an important factor in allowing
<br />an animal population to recover from any effects of a
<br />heavy snow year. whether these effects a~e positive
<br />or negative.
<br />
<br />Sho~t term effects will he temporary. aDd long, term
<br />effects would probably be a.~ociated vith any vegetation
<br />chsnges. Each species has somewhat different habitat
<br />preferences. so it is poasible that each species ~ill
<br />respond in a different way on a long term basis.
<br />Habitat preferences for each small mammal species are:
<br />Ceer mice - south aspects with sparse herbaceouB
<br />vegetation; montane voles - south aspects, probably
<br />with dense herbaceous vegetationi red-backed voles -
<br />conifer forest; long-tailed voles - clear-cut.areas
<br />on north aspects; chipmunks - clear-cutB. near the
<br />edge of the conifer forest.
<br />
<br />-Sigojficance of the Study
<br />
<br />Breedin of all the small herbivorous mammals in the
<br />San Juans witb the possible exception 0 gophers s
<br />inhibited by the presence of snow cover and the b~gin-
<br />jn of breed1n 18 .corr~lated with time of snowmelt.
<br />Thus it shou d poas e,to pre ct tee ect 0
<br />'increased snOwfall due to weather modification on the
<br />timing of the initi.tion of the breeding s..aon pro-
<br />vided the effect of tbe'iDcre..ed .now on duration
<br />of the snovpack caD be predicted. Since air tempera-
<br />.ture. have an equally 8ignificant role in determining
<br />the date of aDowm4!t. :1t ~uld be nec.saary to cOo-
<br />: aider that factor also... ,The result rill nec:e8sarlly
<br />be :SJ1 appro~t1oD ~ith: rather :rlde ~1.m1.ts of unce["-
<br />
<br />t..l:~ty. ., /~~1~t}t~:7~.:; J~~:J~;;~:-. ,~,: ,':. ::': . . '. . .' .. :':'.: ."~' ,
<br />
<br />The actual t!fiect':'on'.t~'~'8ma1l1a&mlMl8 tb'euelves will
<br />be IlIOre ditUcult to assess. A shortened seasoa will
<br />decrease the su.mer.recruitaent of Dew individuals
<br />into the populatioD'~'.i:;:;;;~c;.au:se' .tJ:-~, total DUIllber of
<br />litters is small a,ild the',t:l.e'required to rear each
<br />litter is large in re.lAti~D.._to the total length of the
<br />reproductive 8eason, and;.~.U8e of ,the factor of
<br />synchronization of breed1n&'..Q~:females. it seems
<br />possible that the effeet of the It.itatlon will be
<br />somewhat greater than 4 8~le proportion of days
<br />delayed relative to the day. required to rear one
<br />litter. If the delay results in weaning of any
<br />proportion of first litters_after the cutoff point
<br />(not precisely known) the reduction in recruitment
<br />will be more $ignificant because:tbo8. young will
<br />'probably not reproduce until the fol1ov1ng-ye8['. the
<br />delay will exert its mD8t significant influence on
<br />tbose species whose 'primary habitats l1e on south
<br />aspects. '.
<br />
<br />The total number of births In tbe summer reproductive ..
<br />season is only one component In the dynamics of I
<br />populations, however. and the other compOnents, SU1lllller .
<br />survIval of young and winter mortality at least in the
<br />,..mple of yeat'8 we were observing, were more signiti-
<br />cant in the ultimate determination of population size
<br />than number of y~ung born. Food and feeding habits
<br />as we have indicated above are very slgnificapt fact-
<br />ors in survival of younS and mortality as well 8S
<br />influencing natality directly.
<br />
<br />Broad SiRnificant of Results
<br />
<br />Since ocket gopher populations do not appesr related
<br />to varying sQowpac, t seems un y t at t ey wou
<br />be attected by snowpack augmentat10n. However, it
<br />later lying snow consistently resUlted .1n increased
<br />numbers ot w1nter casts. the 1mpact ot gophers on the
<br />rassland 1.n bringing ~ubsoil to the Burtace and spreac-
<br />ing it over a arger area wou e rester w t t e
<br />the increased snowpac. This corresponds,vell with
<br />findlngs in the alpine tundra ecosystem. Tbe r~ t(' of
<br />sel] r.~vement is not thought so great at the lc~€~
<br />eleVations and gelltler slopes of the fores; eccS~S:'e:.i;~
<br />.50 the ultimate impact ot this etlect 01 pocket gopn~r~
<br />would not be as Irreat in the torest.
<br />
<br />"'!' .,
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