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Breeding Population Inventories and Measures of Recruitment

I. Introduction

E. Species Differences

Different techniques are required for population inventories and measures of recruitment for different groups of waterfowl and for different species within groups. Some of the differences are logistic. For example, breeding geese tend to be in rather discrete breeding colonies or high densities that lend themselves to intensive study, whereas ducks are distributed at low densities over vast areas from high to low latitudes. Some species such as swans are found in habitats where they are highly visible. Other species such as Black Ducks are not conspicuous and frequent habitat where they are difficult to observe. There are also important behavioral differences among species. For example, broods of most dabbling ducks usually seek dense cover or even go onto uplands when disturbed, whereas diving duck broods will move to the center of a pond, where they are easily observed (Smith 1971).

Estimates for rare species require large samples to reduce the variance of the mean relative to the size of the mean. For example, if a sample estimate within 20% of the true mean is required, the sample size required for a rare species will probably not be practical in operational surveys.

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