Breeding Population Inventories and Measures of Recruitment

I. Introduction

D. Differences in Scale

How large an area should be used to measure recruitment? Recruits produced can be measured on a local scale, such as an individual refuge or waterfowl production area, or on a broader scale, such as a state or a continent. Much effort has been expended to measure recruits produced and recruitment rate of ducks on a continental scale (Pospahala et al. 1974, Martin et al. 1979). These efforts always employ sampling and usually involve aircraft. Sampling design of continental surveys conducted by the USFWS has received considerable attention (Bowden 1974, Martin et al. 1979, Johnson 1986).

Recruitment estimates derived from field studies are generally intended to evaluate habitat or specific management techniques on small study areas (e.g., Keith 1961, Dzubin 1969b, Smith 1971, Stoudt 1971, Dzubin and Gollop 1972), although the results are often extrapolated to larger areas. The methodology for conducting local field studies to estimate recruitment rate has not received the same attention as continental surveys.

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