Multipliers- visits

[ειρηνη μαλτσακη]

Hello all,

I have a dataset that some transects were counted twice (2 visits May and June) and some other transects were counted only once. 

Is it enough to create a multiplier with 2 visits and a column -Month- and run the analysis (as we did in Housewren example)? 

Will this be enough to tell the software that for the transects that have 2 counts it should calculate the mean of the months, but for the ones that have only one visit it should take into account only this one?

Thank you in advance! :)

[Eric Rexstad]

Irini

Good to hear from you again. I'm guessing your surveys use point transects, rather than line transects. This is because you are making reference to the house wren example project that uses point transect data. You also mention sampling during May and June which are customarily avian breeding seasons (in the Northern Hemisphere).

If you gathered point transect survey data, with unequal number of visits among point stations, my advice would be to reflect this unequal effort in the data, rather than via a multiplier. Using a multiplier would be easy if all stations had the same number of visits.

I recommend you use the "Effort" column in your project to indicate the number of visits; because with point transects, effort is measured as the number of visits. Here is an example from the "Songbird.dst" sample project

Simply alter the value of "survey effort" to reflect visits to each station.

The estimates coming from analysis of data gathered over two monthly visits will be the average abundance (or density) over that time period.

One other comment, the stations visited only a single time ought to have been "missed" for the second visit "at random." In other words, you should not have deliberately missed stations the second time because "there were too few animals there" or "it is too difficult to access", or other reasons.

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From: distance...@googlegroups.com <distance...@googlegroups.com> on behalf of ειρηνη μαλτσακη <irini...@gmail.com>
Sent: 06 July 2025 13:18
To: distance...@googlegroups.com <distance...@googlegroups.com>
Subject: [distance-sampling] Multipliers- visits

 

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