Re: Data file

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Eric Rexstad

Jun 4, 2021, 12:34:52 PMJun 4
to Hannah Madden, distance-sampling


Yes, as you said, the problem was simple (but tedious). There are some inconsistencies in your data.  Nothing to do with the R code you are using.  As the error message, somewhat cryptically says, for some of your transects your data has provided two (or more) different transect lengths.

It will be a tedious process of sifting through your data to locate those problem transects and provide the consistent correct effort for all detections associated with the transects.  I had a rummage through your data file and managed to find one instance of this type of problem right at the top of the spreadsheet:

crater 35.24 2019 0 BC00A-BC01A 100 1 19
crater 35.24 2019 0 BC00A-BC01A 100 1 3
crater 35.24 2019 0 BC00A-BC01A 100 1 14
crater 35.24 2019 0 BC00A-BC01A 100 1 10
crater 35.24 2019 0 BC00A-BC01A 90 1 19
crater 35.24 2019 0 BC00A-BC01A 90 1 10

You see the first four detections think the transect is 100m in length, but the last two detections think the transect is 90m in length.  The transect cannot be both.  Dig through your data to find other inconsistencies to prevent the error from arising.  Then you can move on to working with fitting detection functions.

On 04/06/2021 16:12, Hannah Madden wrote:

Dear Eric,


Thanks so much for your fast response(s); the list is really useful as I’m still not entirely familiar with the package Distance but I much prefer it to the PC version.


I have been monitoring Bridled Quail-doves since 2016. In 2017 we were hit by 2 cat-5 hurricanes and since then the population has declined drastically. As I said yesterday, this year we only got 34 detections. Here is the ‘flatfile’ I am trying to use – it worked earlier but when I made some adjustments I now get the error relating to Effort. From the lemur example I see that Area was 0 so I put 0 as well, but the entire survey area is 440 ha. I attach the R file.


Really appreciate your assistance with this,






Hannah Madden, MSc

PhD candidate

Caribbean Netherlands Science Institute


Tel: +599 318 2040


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