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Nesting Density and Success of Prairie Falcons in Southwestern Idaho

Verland T. Ogden and Maurice G. Hornocker
The Journal of Wildlife Management
Vol. 41, No. 1 (Jan., 1977), pp. 1-11
Published by: Wiley on behalf of the Wildlife Society
DOI: 10.2307/3800084
Stable URL: http://www.jstor.org/stable/3800084
Page Count: 11
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Nesting Density and Success of Prairie Falcons in Southwestern Idaho
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Abstract

Fifty-six, 74, and 101 prairie falcon (Falco mexicanus) nesting territories were observed along 72 km of the Snake River in southwestern Idaho during 1970, 1971, and 1972, respectively. Nesting success averaged 83 percent during the 3 years of study. Clutch size averaged 4.3 eggs in 68 nests visited. An average of 3.5 young hatched and 3.1 young fledged in 110 nesting attempts; 3.7 young fledged per successful attempt. Townsend ground squirrel (Citellus townsendii) was the prey species found most frequently in prairie falcon nests; horned larks (Eremophila alpestris) and western meadowlarks (Sturnella neglecta) were found less frequently. Egg mortalities totaled 37 percent, and infertility accounted for 11 percent of 300 eggs counted. Nestling mortality was 17 percent of 221 falcons hatched in 1971 and 1972. One-half of the nestling losses was due to unknown causes; and other losses were due to predators, disease, and interspecific conflicts. Mean thickness of 38 unhatched eggshells was 0.319 mm. Based on these data, the population is considered reproductively healthy and stable or increasing.

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