Measures of abundance

One of the basic concerns of field work is to develop a sense of how much is out there. In a recent presentation I encountered a fascinating study in which the researchers were studying a shore bird called the Wilson’s plover. This bird is a beach nester that is not too common, but not endangered.

One of the foods of choice for the bird is the hermit crabs. The food source lives in burrows along the shore in muddy zones. The crabs dig burrows. A knowledge of the number of crabs in the nesting are used by the Wilson’s plover provides information about the available food supply. The measure of abundance in this case is the number of crabs and not the weight of the crabs.

The present sampling strategy is to toss a quadrat, a wooden square in this case, onto the mud flat where the crabs live and to count the number of crabs in the frame. Crab counting is hard. They move. They hide. The strategy used today is count multiple times and use the average number of crabs as the estimate for the selected quadrat.

A short discussion with the researchers demonstrated their knowledge of sampling and its issues, but they were not aware of 2 things.

  1. They were not aware of counting frames
  2. They were not aware of the efficiency of SRS

This isn’t surprising since stereology is a relatively unknown science.

The researchers will be doing more studies next year. They know that it is better to count burrows than it is to count crabs that run and hide. They are likely to use the counting frame and SRS in next year’s study.


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