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, leplicatlon of the Effects of Cloud Seedlng on 5mBll _to Whether cloud ...dlng 1. good or bad Is a value judg- ~at that 1nvo~v.. a cODPleX .yltem. Since deer mice ahoved the Br..teat relatIonship with snowpack. 1 vill u.. thi. epaet.. .. an example of the complexity. ~.r ate. prt.arl1y .at ...da during the winter (John.on 1962~ Vau.han 1974). Althouah deer mice occur ..inly on the louth ..pacta, they do invade north ..pecta when population denaiti.. are high; where, beeau.. of thelr ...d ..ting babita, they could po- tantielly lnc.rfere with natural reforestation of eenif_r.. .a _now ack relult. in a reduction of deer aice aD ao ..r a ca ar. on t . north a an or..tara ~ he than con.ider cloud ...din oDd. er ca.. r..r y on neecta durl~g the summer, .. t t. u 0 t e eer mouse popu at on on t e south .. ect....tn.r. coUld De a reductlon ot herbl- .. Yoro~ n..gt. an t ua more orase wou rema n or an ca .. e. a usn a re uc on .er atee '.0 rane .r. an untara coul cona1dei cloud ...dlal~b.d. Thi_ ax.~ a 8a pr..ente two .Id.. to tha t..us of cloud aeedlng 1n relation to .ear .ica, yat.evan thh i. a a"'.plffleation h_c.,urH" t~re are un)'_ othar inuractiona that could be con- aidered bafor. ..Una jud..lllant.. When condch:lrtnR .11. the .pacla,a,;of ...11 ......1.. the .yetem hecolMs aV~llP.r.- cOIIPlu:!., HaD,. int.ractiona wera not studied dud.D,','tba C~...~..of .chi. project. Decidona ud. .01.1y on"th.~~~.ca.,of; thh project could be II!none- OUA. becau.. of the limited acope of this project. Extrapolation of r.aults in ~y study to other areaR of the montane ecosystea might not be appropriate. Vaulhan (1969) atudled montan~ small mammel8 In northern Colorado. His data show different population t~.nda in relacion to anovpack. although he did not q~ntify his anovpack data. Summary Substantial hOme ranle data were obtained on deer mice during the snow fr.. period of the y.ar. During the fire: 3 months after snowmelt, daer mou.. home range ,~ze was highly correlated (r--0.90) with population ~ze. Hypothesia A (Summertime haDe range will be uaaffected by snowfall) would be accepted for deer .!ce, becauae of the relationship of home range to population 8i... Snowpaek only hae an indirect effect oa home range through population size. nata were ia.uflletent to ..ke conclusions on Hypothesia A for tbe o~her four .pecies, but I expect the hypothesis would be accepted if sufflcient data were available. Hypothe8is B (Inereased Bnowfa!l will increase mortality rates in the winter of occurrence and the summer follow- ing) would not be accepted for any species, becauae of its two parta. There are data to anawer the first part, but the phr..e lIand the aWlllllef following" cnakea the hypotheaia too broad to be teatable, because au...r and winter ~rt.lity appear to be affected by dilferent variablea. nen.ity est~t.. for five .peei.. of amall mammal8 were 'obtained. during each live trappin. period. Sam})l. atzea varied gr..t1y, with deer ~. providing the beat data and loog-tailed vol..!prOYidins the leaat reliable data. Deer mou.. population aize had a atrong negative ralationship with 8oowpack. and chip- munk population 81ae had . weak negstive relationship vith anowpack. The other three apecie. reacted to variable. other than anovpack, thus obacuring any relation.hip. with anowpack. Annual variability in anovpack is probably an i_portent factor in allowing an animal population to recover frOM any effects of a heavy anow year. whether these effecta Bre positive or neglttve, 33 Short term effects will be temporary, and long term .tlects would probably be as.ociated with any vegetatio changes. Each species has aomewhat different habitat preferencea, 80 it 18 posstble that each splI!cies wlll r.spond In A different way on a long term bssis. Habltat preferences for each small mammal species nre~ neer mice - Bouth aspects with sparse herbaceous ve,.tatlonj montsne voles - south aspects, probably with denA~ herhacaoua vegetation: red-backed volPA - conif~r forest; long-teiled voles - clear-cut arr.na on north aspects; chipmunka - clear-cuts, neAr thp edle of the conifer forest. -Sian I fIr Anee of the Study Br.edin~ of all the small herbivorous mammals ill the S.n Juans with the pOBsit'lle exception of gophers is inhibited by the presence of snow cover and the..~!!,gli}-' in of breed!" is correlated with time of snowmelt. Thua t. shou e pOlS e to pre ct t l! e Ie:Ct:- or increased snowfall due to weather modificaRonoii -the timlng of the initiat1.on of the breeding season "pro- vided the effect of the increased snow on duration'" 'of the snovpRck can be predicted. Since nir t~mp~r~- 't';.rPM TIn";,.' n"-~qu.ll)' af~ificAnt 'rule In detf'rmilllllR the dntr (I[ snowmq!t, it would be necessary to Cfln- ~fder lhnt f"ctor also. The retH.llt will n("t"('~rt"rt Iy ht' All tlrl"ruxlmt'ltioll w1 tll rather wide limit!! nf lJlll'('T- tl\int)'. l'he actUAl effect on the 8mall mammals themselves will be'more difficult to asseas, A shortened season ""ill- decrease the aummer recruitment of new individuals into the population. Because the total number of litten is small and the time required to rear each Utter 19 hrge in relation to the total length of the reproductive season and because of the factor of synchroniEation of breeding among femalea, it seems possible that the effect of the limltation will be somewhat greater than a 8i~ple proportion of days delayed relative to the days required to rear one 11tter. If the delay results in weanlng of Any proportiCln of first litters after the cutoff pOillt (not prechely known) the reduction in recruitmPllt will be more significant because those young will probably not reproduce until the following year. The delay will exert its most significant influence on those apecies whose primary habitats lie on south aspects. The total number of births in the summer reproductive season is only one component 1n the dynamics of populations. however. and the other components, summer survival of young and winter mortality at least in the sample of yesrs we were observing. were more signlfi- cant in the ulti~te determination of population size thsn number of young born, Food and feeding habits 88 we have indicated above are very signif1c8(1t fact- ors in survival of young and mortality as well 88 influencing nstality directly. Brood SiRnificsnt of Resulta Since ocket gopher populations do not appear related to varying sQowpac. t seems un e y at ey wou a- b. affected by snowpack augmentatlon, However, it later lying snow eonaistently'r.sUItid 1n 1.ncTe8sed n ere 0 w n ar cas a, t 8 mpac 0 gop ers on t c raa. an n r ns n ..u.o 0 e eur aee an 8prea~- DI t OVar a arger area wou e great~!_~ _t.... .t. .e.. ..~. t'iie!;creued enowpack. Thi8 corre.ponds '....ell wll:h findlnge in the alplne tundra ecosystem. The r:!tC' o! sclI r.IC'vement is not thought 80 great at th.", lct.:cr ~l(>WJt:lonR and gelltler slopes of the fores," eC(l$Yf;~.l';'l~" :'If! the,> uHitnllte impact of thls eUect ot p'lck~l giii'ilit:i'n' would not be aa great 1n tile toreot.