Laserfiche WebLink
<br />fi <br />.~ <br />f. <br />.' <br />i-;., <br /> <br />"' <br /> <br />Life Requisites <br /> <br />i.~ <br /> <br />.', <br />" <br /> <br />Peregrine falcons feed on more than 20 species of birds and several small mammals (porter and <br />White 1973). Hunting areas included marshes or narrow tongues of streamside vegetation, and <br />peregrine falcons may forage up to 17 mi from nest sites. Peregrine falcon diet at nest sites in <br />national parks in southern Utah included small and medium-sized birds, especially including white- <br />throated swifts, large shorebirds and Clark's nutcracker (Burnham 1987). <br /> <br />";:'. <br /> <br />J" <br /> <br />In Grand Canyon, peregrine falcons feed on waterfowl, swifts, swallows and bats (Brown f991a, <br />Stevens personal communication), which feed on invertebrate species (especially Diptera) that <br />emerge out of the Colorado River (Blinn et aI., 1992). Therefore, dam operations that influence <br />aquatic macro-invertebrate populations exert indirect impacts on peregrine falcons. <br /> <br />".1 <br />I <br /> <br />.,~ <br /> <br />V> <br /> <br />Peregrine falcons breed up to 3,130 m elevation, typically on ledges on steep clifffaces (U.S. Fish <br />and Wildlife Service 1984). The mean distance between nest sites along the South Rim of Grand <br />Canyon varied from 3.5 to 5.0 linear miles, with minimum distances of 1.8 linear miles (Brown <br />199Ia). The breeding season in Grand Canyon extends from February to July. <br /> <br /> <br />The primary reason for the national decline of the peregrine falcon population has been eggshell <br />thinning from DOE and other environmental contaminants, which are biologically concentrated <br />through the food chain. DDE sources to peregrine falcons are derived from their prey,lIWlY of <br />which are migratory insectivores. Burnham (1981) reported that swifts, shorebirds, andother <br />migratory insectivores contained 5.8 ppm DDE (wet weight), while mean DDE levels in <br />granivorous migrants, such as grosbeaks and mourning doves, was only 0.14 ppm DDE. <br />Peregrine eggshells from soutliern Utah parks from 1985 to 1981 were 21% thinner than those <br />from the pre-DOE era, indicating poor viability of eggs (Burnham 1981). Brown (1991 b) <br />reported that peregrine falcon eggshells from the Grand Canyon in 1988 were 11.4% to 12.7% <br />thinner than pre-DDE controls. <br /> <br />ti. <br /> <br />.'c <br />"-'. <br />.... <br />...... <br />~< .., <br />r<;, <br /> <br />i;~,~; <br /> <br />~<;?. <br />,:>.,.: <br /> <br />In addition to pesticide concentrations, competition with other raptors has been considered as a <br />possible cause of peregrine falcon population declines; however, Porter and White (1913) <br />examined peregrine and prairie falcon interactions and concluded that competition was not <br />important <br /> <br />~' .-, <br /> <br />!i~': <br />if., <br />~, ;,.;. <br />1::'1;:. <br />;~~i~: <br />:~ <br />. ""~ <br />~~:t <br />\'..'.. <br /> <br />Effects of the Proposed Action on Peregrine Falcon. <br /> <br />Food sources are only indirectly influenced by dam operations. Therefore, peregrine falcons will <br />not lack food resources during the proposed high release. The flow will not alter peregrine falcon <br />habitat. <br /> <br />.--;-~ <br />'l;..... <br />"'-';', <br /> <br />The October test flow will have no effect on peregrine falcons in the Colorado River downstream <br />from Glen Canyon Dam. <br /> <br />24 <br /> <br />ii' <br />