Surveys carried out from multiple land-based survey locations

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Melissa Costagliola - Ray

Mar 30, 2022, 4:21:22 AMMar 30
Hi all,

I am currently working on a dataset of seabirds counted from land-based vantage point surveys (point transects) recorded from three locations within a single tidal channel (Figure attached).

My question is: Is it appropriate to carry out distance sampling on this dataset as a whole, or will I have to fit detection functions and estimate density and abundance (of different species) per location (i.e. VP1, VP2 and VP3 from the attached figure)?.

I really appreciate any help you can provide, and thank you in advance.

Best wishes,

Melissa Costagliola-Ray

Eric Rexstad

Mar 30, 2022, 4:35:18 AMMar 30
to Melissa Costagliola - Ray,

There are challenges to the analysis of the survey you describe.  They are highlighted in section 11.1.1 of Buckland et al. (2015).  Specifically, the points are not randomly placed with respect to the birds and the birds are aware of the location of the points.  It is unlikely that birds are distributed at uniform density at all distances from the points (the "design assumption" Section 1.7 of Buckland et al. (2015)).

This means that to properly analyse such data, not only would the detection function need to be estimated but also the animal gradient would need to be estimated (because its shape cannot be assumed).  There are published methods for performing such an analysis

Marques, T. A., Buckland, S. T., Borchers, D. L., Tosh, D., & McDonald, R. A. (2010). Point transect sampling along linear features. Biometrics, 66, 1247–1255.
but a) there is no software to perform such an analysis and b) such analyses depend upon more than 3 replicate points.

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