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~~ <br />r <br />r <br />r~ <br />r <br />r <br /> <br />period. A few boxes were checked twice and a shift in types of <br />food were noted; the most common shift was from an earlier use of <br />a larger portion of mammals to a smaller proportion and greater <br />use of reptiles or insects. A summary of Kestrel diets by <br />Sherrod (1978) mentioned reptiles in a small proportion of any <br />analysis. The ability of Kestrels to either alter their hunting <br />behavior or recognize a more abundant prey base probably enabled <br />them to produce fledged young. The Starling, which is restricted <br />to an insect prey base would be unable to change to an alternate <br />food source. It was noted that during May, when box checks were <br />stopped due to a shortage of personnel, 8 of 40 Starling nests <br />had lost 1 or more juveniles. <br />Table S. Food remains visually observed in Amerian Kestrel nests in Idaho and North Dakota during 1988. <br />Parameters Idaho North Dakota <br />Number of news 22 14 <br />% o[ nests with i1vNC 82 (5-100)° 93 (5-95) <br />:G of nests with mammals 41 (10-100) 86 (30.100) <br />°,4, of nests with buds 23 (200) 29 (10-70) <br />°~6 of nests with reptiles 50 (5-90) 7 (75) <br />numbers in pazenthesis aze the range of °h found m boos for that type of food remain <br />Kestrels are dimorphic in size with adult females being <br />approximately 10-15 percent larger than males (Roest 1957). <br />Young are felt to show differences in size between sexes <br />beginning at 6 days of age (Bird and Lague 1982). We grouped the <br />young into 5-day intervals due to possible judgement errors in <br />age. Sexual size differences were not evident until the 15 days <br />of age period (Table 6). <br />