[Dominik Marchowski]

Hi,

The premise for calculating the density in Distance is that in the first sector - closest to the observer, the most objects are (the assumption is 100%). I know that under different circumstances it may change, e.g. the scaring effect of an observer. I suppose that the chart I am enclosing may be evidence of the observer effect. My question is what would be the result if we compute the data arranged in this way using Distance without any correction? Will it be an overestimation?

All the best

Dominik

[Eric Rexstad]

Dominik

The detection function fitted to these data will not reflect the process that gives rise to detections.  Instead, it will reflect detectability along with the non-natural distribution of animals possibly induced by responsive movement caused by the observer.

We cannot know the true shape of the underlying detection function in the absence of responsive movement, so we cannot made a determination regarding the direction and magnitude of bias induced.  But it can be said analysis of such data will produce a biased estimate of density.

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Eric Rexstad
Centre for Ecological and Environmental Modelling
University of St Andrews
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