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<br />Pcrcy;rlncs, page '4 <br />riackgrowtd Nnteria7: <br />The American peregrine falcon (1•". p. ^na[um) cnrrr.nt.ly broods across Che <br />Unirod States from the Cail;a oC Alask:.t south Lo L'aja CaJif.ornia, rentra.l Arirona, <br />southwesC 'fexa::, ^texi.co, Colotado and wyoming, w.i.ntering chiefly on its breeding <br />rant;c with Chc morn nurthorn birds moving sancwhoL south in the winter. (Snow, <br />1972). <br />A 1964-65 survey estimaCOd appro>:imatcl.y 25 brecrling pairs in Co].orarlo and <br />WyomiuP (Cndrt'son, 1969). A cursory 1972 sCudy indicated six active eyries wiCh <br />pairs and two with lone birds in Colorado (Lndcrsou, 7.972). There arc perhaps <br />200 brecdi.ng pairs of :utrCUm in the continenCal United States at p mscnC (Hnderson, <br />1972). <br />Young (1969) consCrucCCd a hypothetical populaCi.on model Eor peregrines with <br />the fol]owing reasonable assumpCions: longevity, 20 years in Che wild; yearling <br />mortality, 66.6% per year; adult mortality, 20% per year; nesting success, 60'/, <br />per year; productiv~iCy, 2.5 fledglings per successful nesC per year. ldith these <br />parameters the population maintains itself. IC adult mortality is increased by <br />]0% there is a 5'/, drop in populaCi.ou each year. A .10"/, increase in mortality over <br />a tltrcc year period results in approximately a 12% drop in CoCal population. If <br />productivity is reduced by 10% there is a 6"/, decrease in population in the same <br />time span. IC nest failure is increased by 10% in three years there is a 5% <br />population loss. It would appmr that adult mortality is amore important factor <br />than either decreased productivity or increased nest Failure (Snow, 1972). lE <br />each of these factors .is increased by 10% [here is a 22% loss oC Chc population <br />in Chree years. Ten percent: is not a very large increase, but there. is a sion~i- <br />ficant impact on populations. <br />NaCUral predators have l.i.[tle eClecC on pere};rincs, thrir most serious <br />enemy bcint; man. Peregriucs at nest siCes arc vulnerable Co shouting, bite the <br />impact. of shouting is unl:noom. human ltaras:;ment in the form of disCUrhancc at <br />eyries is a serious (acCOr in some siCuaCions, particularl.y.in parts of Chc Nest. <br />Rock climbing is an increasingly popular activity, and if conducCed near eyries <br />during Che nesting season may cause abandonment. Some birds arc c>:ceedi.ng.ly <br />sensitive to disCUrbance and wi7.1 abandon if humans have been anywhcm. near the <br />eyrie. (Snow, 1972). <br />A basic component of the habitat is a cliCC. These arc the nwsC conmtonl}' <br />used nesting si.Ce. Utili.zod cl.i.ffs are often very high, frequently overlook <br />water, and often command an esCcnsive view of surtoundin}; cotmtryside (Hickey, <br />1942). Hot.cvcr, thcrr. arc malrv such cliffs in the western stoCes which arc noC <br />occupied by pere7;rincs, for unkno•.an reasons (:;rota, ]972). Cade (1960) fcr•l.s <br />that tCadLliO^ is a facCUr .linkinJ; goneraCiuns uC perel;ring: to the same cliff. <br />Tfates return co rlte same eyrie each year, when one mate dies, Chc other acquires <br />a new mate, if. both birds d7.e ac once the seyue.nc.e is broken. 1'he cliff may be <br />reoccupied inuncdi,~tely by other fnlc.c+ns or 'it may novor be used again. UCili- <br />zaLion of. c.li.ffs also Jepcuds upuu changing envirunmenCa]. r:ondi.Ci.uns around Chem, <br />such as m;tjor altcraciun,: of the cuvironmcnt by human occupaucc and dtangcs in <br />avai.labi.liCy uf: prey (Cade, 1960; Iliclury and Andorson, 1969). "fhc nwnGcr of <br />di(L[•reuL~nosl.ing ledge:; used h}• a s~i.nf;lr pair of pcro£rinos over a loaf; period <br />of years may vat}' from unc er lwu u, as many as coven. Thr ma>:imuw disCancc <br />beCwcen alCernate cliffs in diEfercnC years may e::cc~~d (our miles. RnnesLin};, <br />