0 detections

[Cheryl Lohr]

Hi folks,

So probably really stupid question here, but using R package 'Distance' should I list size=0 for any survey points where zero birds were detected?

Using point-transect method.

Thanks,

Cheryl

[Eric Rexstad]

Cheryl

The proper way to organise your data so that the Distance package recognises you visited point count stations without making detections is shown in example data provided with the Distance package:

> library(Distance)
> data("Savannah_sparrow_1980")
> head(Savannah_sparrow_1980, n=10)
   Region.Label Area Sample.Label Effort object distance Study.Area
1     PASTURE 1    1    POINT   1      1     NA       NA  SASP 1980
2     PASTURE 1    1    POINT   2      1     NA       NA  SASP 1980
3     PASTURE 1    1    POINT   3      1     NA       NA  SASP 1980
4     PASTURE 1    1    POINT   4      1     NA       NA  SASP 1980
5     PASTURE 1    1    POINT   5      1     NA       NA  SASP 1980
6     PASTURE 1    1    POINT   6      1     NA       NA  SASP 1980
7     PASTURE 1    1    POINT   7      1     NA       NA  SASP 1980
8     PASTURE 1    1    POINT   8      1     NA       NA  SASP 1980
9     PASTURE 1    1    POINT   9      1      1     25.3  SASP 1980
10    PASTURE 1    1    POINT  10      1     NA       NA  SASP 1980

The field "Sample.Label" indicates the different point stations.  Note that of the first 10 stations visited, a detection was only made at station "Point 9", where the distance of 25.3 was recorded.  For all other stations, where there were no detections, the "distance" field contains the indicator NA, representing 'not available', as there was no distance at which animals were detected. A row must exist for each station visited so that the Distance package properly recognises the amount of survey effort.

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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