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- ".,-.-~-_..,,--. ...,.....-,_. ,-1 \ ,-' EU Hm'L"itNTS At'.'t; CALVIN(, AS RE.LAT[]I ',"e"n'''' .?/ ~nd n. \:'. Jllr:l{'f' to:. .., ~. .. n TO SND\.: COVER .v Stdnh"ff ABSTRACT A 4-year study was conducted in the San Juan Houn- caimar southwestern Colorado to dctermlne the e1Tects of snow on the di&tTibution and calving of enz-rcervus- canadensie). Seventy-five aerial surveys resulted in 1262 'Wlnt~'t' and 2325 spring elk s1ghting9. Measure- ments of the sno~ack Yere obtained tn areas of winter ell<. e'lghtings and at 31 pennanent snow stake si tes to quantify the critical depth of snow for elk and to estimate winter range. Ground surveys provided supple- mental information to the spring flights fOT the eval- uation of calving. The initlation and pattern of elk migration were regulated by snow cover. Sno~ depths approaching 40 em (response depth) caused elk to move to more exposed w1nte~ T~ngel if such wes'~vailbble. Areas vith ~re than 70 ,em (crit1a1 depth) snow cover were avoided.' South aspects and ~adow cover types ~re used by elk ~re than other habitat types during the winter perlod~ Estimates of vinter range indicated that a 15 percent increase in snovpack may decrease to~.l winter range by 0 to 20 percent dependent upon present enoW conditione. Spring moVement of elk back into the high summering areas was associated more strongly with tbe greenin& up of the open ncuntain meadov. than directly vith . receding anow line. Calving occl,1red between tr.1d-Kay and lD.1d-June at an elevation of 2800 to 3200 meters. Each 8~ason there appeared to be ample habitat available for calving below the snow line. INTRODUCTION Just1fic4t1on Elk (Cervus canadensis) represent a valuable natuTal resource. In 1968, hunters in Colorado spent over $19 ~11110n on goods and services in conne~tlon with elk hunting '~(Nobe .and Gilbert 1970). The tremendous esthetic aP9~al of the ~ild wapiti further Increase6 the value of this big game species. With such a pub- ltc investment tn~Qlved. .ny .action ~hat might affect the elk populations should be scrutinized carefully. In 1961, Congress directed the Bureau of Reclamation to conduct research on weather modification, thus initisting llProject Skyvater". Within this nation- wide weather modification research effort, the Colora- do River Bssin Pilot P~oject was established to test fully the operational status of winter cloud seeding. The test site for this pilot project was a 6500 sq k~ area of the San Juan Mountain Range of southwe~tern Colorado. Much of the target area vas abo~~ 2900 m elevation. Coope~and Jolly (1969) cautioned that "AlthQugh the snow Il\8nage~nt progt:am contemplated by the Bureau.'of Reclamation and other wate.r sup- ply agen~ie6 ~a initially to be directed mostly to- ward high mountain zones of deep snQw not used by big tame during winter, spillover to lower eleva- tion is not i~po6sible.. The effect on wildlife populations might be significant. Perhaps more i~portsnt fro= the standpoint of the operating sgencies, the Public ~y believe in such an effect even if it does not exist. ~ildlife is a ~ubject with such high emotional content that Strong efforts should be ~d~ to ensure that animnl pop- ulations are not advetseJy gffected by "'eather mod- ification, and that the pUblic is .!l....ar~ of this." - :Secftcms 0",; 1I"'_d. CONCLUSIOBS THe follo~ing ton~lusions ~ere draWn for th~ elk popul8tion on Missionary Ridge: Hypothesis 1 - Critical Snov Depth 1. The initiation of winter mig~atlon of elk is in res onse to increasin snow cover. 2. Snow de ths a roaching 40 cm response depth) cause elk to move to more expose w neer range if such is available. .! 3. ,Snow depths in excess of 70 tm usually prohibit the use of an area by elk, and is considered' the C~~t1cal depth at snow tor elk. Hypothesis l - Aspect Preterence 4. ,There 11181 be a preferential use by elk of south .spec~s and/o~ meadow cover types d~rin8 the winter seaSOn. - Hypothesis ) - Winter Range S. Winter ran e decreases with increasing Cover and may be decr~ased an average by cloud see "8 percent ncreaSe pack) . 'Hypothesis 4 - Spring Migration 6. S rin mi ration of elk ia associated more ron 1 with reen n up 0 t e open moun ain meadows than directly v t t e rec, n8 8no~ line. However. 1n late springs the reced1ng zone of partial snow'cover may ~4mlC co some degree the movement 0 as muc as the elk herd, ;H:tl'othesls ~ - t:..ll';. calving wcation : 1. The ma ority of elk calving occurs between mid- Kay and mid-June at elevations or LDUU co JLU . i 8. The recedin snow line in most cases does~not I affect the location 0 calving. ,Hypothesis 6 - Elk CaLv~ng ~1tes ' 9. Each 8 rin there appeared to be ample habitat for calvin below t e zone 0 part a snow COver. 10. Favored calvin sites are c racter ze yam x- ture of t1~ber cover An small open ngs w t southerlv exposure. , snow percenl n 8noW- 11 1/ In St~inhoff. ".W., and ~ountains I Colorado. Present Address: Dept. .T.D. Ives (Eds), 1976. Ecologjcal impacts of sno~pack a~gmentation in the San Juan 5dn Juan Ecologr Project, FinaL Report. Colorado Stat,e Univ. Publ., FOl:'t CclJ,im:, of Forestry. Universjey of Arkansas at Monticello, Monticello, Arkansas 71655 415 1o._s:l.A_J,