Distance sampling on extended fixed-point count

[Mei-Ling Bai]

Dear group members,

The German StUK4 is a guideline for investigating the impacts of offshore wind farms. One of the methods it suggests for studying migratory birds is to conduct extended visual observation at a fixed-point, recording bird species, number, and distance to observers. Since the assumption of "a snapshot" is totally violated, can we still apply the spirit of distance sampling in such analysis?

Thanks a lot for any discussions!

Mei-Ling

[Eric Rexstad]

Mei-Ling

The application of distance sampling methodology to fixed point of migrating birds seems dubious.  As you note if the observer if stationary (on an anchored boat or platform?) then all birds are moving faster than the observer and animal movement will inflate the estimates of density or abundance.

It is beyond my intelligence, but I wonder if the sampling design you describe might (with sufficient replicate stations) be akin to a camera trap type of distance sampling analysis.  The difference between a camera and a human observer is that animals (largely) become habituated to cameras, whereas there is unlikely to be habituation to observers on an anchored platform.  As a result, the distribution of birds at distances from the platform is probably deformed from its assumed 45degree distribution.  Guess that thinking in print didn't really lead to useful insights.

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Eric Rexstad
Centre for Ecological and Environmental Modelling
University of St Andrews
St Andrews is a charity registered in Scotland SC013532