File:Brigham Young University science bulletin (1955) (20228624709).jpg

Title: Brigham Young University science bulletin
Identifier: brighamyounguniv18brig (find matches)
Year: 1955 (1950s)
Authors: Brigham Young University
Subjects: Biology -- Periodicals
Publisher: Provo, Utah : Brigham Young University
Contributing Library: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library
Digitizing Sponsor: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library

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54 BnicnAM YouNO Univfusitv Science Bulletin and R. D. Porter (unpuhl. data) ohscrvt-d a Prairie Falcon feeding on an ibis at the Bear River marshes on 5 June 1951. Since the ihis was not found in the evries of either species, it was prol)ahl\- too heavy for the falcons to carry to their eyries. The weight of an adult female ibis as determined by Porter et al. (unpubl. ms) is 517 grams, whereas the weights of two adult female avocets average 281 grams. In Prairie Falcon eyries along the Wasatch Mountains, shorebirds, passerines, rodents, and gallinaceous birds were nearlv equally repre- sented; whereas in the e\ries of the peregrine, shorebirds predominated and gallinaceous birds and rodents were absent (Table 5). The ducks present in the eyri(«i of the Prairie Falcon (Table 5) were about half grown and probably inca- pable ot (light. Hence, the\ probabK were either captured on the water or on the ground and were sufficiently light in weight that thev could be carried hv the falcons. We have no data for comparison of the food habits of the peregrines nesting in the desert (Table 6) with those of desert-nesting Prairie Falcons in the same region. A comparison of this kind is needed to fulh' evaluate the compe- tition for food by the two species. Cade (1960) found that the overlap in food species of the peregrine and Gvrfalcon were least in the areas of contact and greatest in areas where ranges were not s\mpatric. A comparison of this kind between the peregrine and Prairie Falcon would be difficult to make, since in Utah the Prairie Falcon occurs in the same geographic area as the peregrine. Nevertheless, one would expect
Text Appearing After Image:
,« ^ F"ig. 39. Prairie Falcon feeding its voung a downy avocct (peregrine site 7, alt. prairie site 2, see Fig. 26). Photo l>v W. 1. Erwin and'IL I). Porter, 1948.'

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