. Brigham Young University science bulletin. Biology -- Periodicals. 58 Bhicham Young Univehsitv Scmknt k Hi' Fig. 43. .\ cliff used alternately i)y I'rairie Falcons anil ravens. Nesting site is situated in a pothole similar to that shown in I'igure 4(1 Cliff is less than 2 miles ( km) from the peregrine eyrie shown in Figure 22, and this cliff may also have hecn used historically hy peregrines. Photo hx l\. J. Erwin. August 1972. Prairie Falcon arc incomplete in regard, all but one of 36 Prairie Falcon eyries in Colorado and Wvoming reported 1)\' (1964) were directh
. Brigham Young University science bulletin. Biology -- Periodicals. 58 Bhicham Young Univehsitv Scmknt k Hi' Fig. 43. .\ cliff used alternately i)y I'rairie Falcons anil ravens. Nesting site is situated in a pothole similar to that shown in I'igure 4(1 Cliff is less than 2 miles ( km) from the peregrine eyrie shown in Figure 22, and this cliff may also have hecn used historically hy peregrines. Photo hx l\. J. Erwin. August 1972. Prairie Falcon arc incomplete in regard, all but one of 36 Prairie Falcon eyries in Colorado and Wvoming reported 1)\' (1964) were directh' ovcrhinm li\ a |iortioii of tiie clifl. Size Preference for Nesting Area The Prairie I'"alcon appears to he less selec- tive than the peregrine in the size of its nesting or egg-laying area. White (nnpnbl. data), for in- stance, ohserved a Prairie I'alcon nesting in a pothole that was appart>ntl\ too small for a large family of \()inig because, Ix'fore the vonng had fledged, all but one were forced from the c\rie to an unlimelv death on the talus below (Figs. 45-46). This nest was used for fi\e consccutix'c years. The female laid five eggs each vear and each vear onl\ one \onng fledged. The e\Tie was then abandoned. We have also, however, seen prairies successfulh' fledge large broods from ledges e(|ual to or smaller than the site men- tioned above. The aforementioned Prairie Falcon e\rie in Weber Coimt\ that was taken over b\' ravens liad a total, nesting area of only about 310 sq inches (2,000 cm'-) (measured from photographs). A Prairie Falcon e\rie in Box Elder Comity, found bv Erwin, was in a crevice in the face of a cliff wiiich was onlv 20 inches (51 cm) wide at the point whcr(> the eggs were laid. The crc\'ice was over 80 inches in depth (ca. 200 cm) and nearlx high enough for a man to stand in (mea- sured from a photograph). In the Wasatch Mountains, peregrines usual- ly laid their eggs on wider ledges with a relative- Iv more spacious nesting area (fref|u
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