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Territorial Behavior, Pesticides, and the Population Ecology of Red-shouldered Hawks in Central Maryland, 1943-1971

Charles J. Henny, Frederick C. Schmid, Elwood M. Martin and Larry L. Hood
Ecology
Vol. 54, No. 3 (May, 1973), pp. 545-554
DOI: 10.2307/1935339
Stable URL: http://www.jstor.org/stable/1935339
Page Count: 10
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Territorial Behavior, Pesticides, and the Population Ecology of Red-shouldered Hawks in Central Maryland, 1943-1971
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Abstract

A breeding population of red-shouldered hawks (Buteo lineatus) along the Patuxent River in central Maryland was studied during the interval 1943-71. Numbers of breeding pairs remained unchanged or increased on the PWRC (Patuxent Wildlife Research Center) and an adjoining area where habibat was not altered. A reduction in breeding pairs occurred on the third study area where large portions of the habitat had been destroyed. Basic information on 74 nests was obtained and the annual number of breeding pairs on the PWRC ranged from a low of four to a high of nine during the study. Nesting success of this highly territorial species decreased significantly as the distance between adjacent nest sites decreased (Errington's principle of inversity). Since 1960, the recruitment rate during "high" density years was 1.34 young fledged per pair as opposed to 1.95 during "optimum" (1943 and 1947 levels) density years. The 1.95 figure compared favorably with the estimated recruitment rate necessary for maintaining a stable population and with recruitment rates observed in other locations prior to the modern pesticide era. As the observed recruitment rate during the 4 years of "optimum" density was believed adequate, it is doubtful that the relatively low pesticide levels in the eggs had a detrimental effect on the reproductive performance of the population.

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