[tlocoh-info] WG: nsv and mnlv

[Andy Lyons]

Hi Julia,

Good questions. See some comments below. Also take note:

1) Version 1.17 of the T-LoCoH package has a bug. If you updated to that 
version, *please update to v1.18* (which was posted today)

update.packages(oldPkgs="tlocoh", repos="http://R-Forge.R-project.org")
or
install.packages("tlocoh", repos = "http://R-Forge.R-project.org")

2) There's a new tip sheet about time-use analysis on the website that 
you might find useful, see 
http://tlocoh.r-forge.r-project.org/tips_faqs.html.

Other comments below:

On 9/9/2014 6:33 AM, Julia Krejci wrote:
>
> Dear tlocoh-list,
>
> I've calculated revisitation rate and mean duration of visit for some 
> birds I put GPS-transmitters on.  I chose an inter-visit-gap of 12 
> hours. Maybe I'm already work-blind, but I can't seem to understand 
> the intervals the output gives me.
>
> If I display the nsv data, it shows me all points which are considered 
> as consecutive visits to a hull, right? And the colour code shows if 
> the individual was there rarely or often. The intervals of my output are:
>
> 1 -- 11.6
>
> 11.6 -- 22.2
>
> 22.2 -- 32.8 ... and so on.
>
> So, this means, the individual revisited this hull once or 22 times 
> during one inter-visit-gap? That doesn't seem right. I'm quite sure 
> I'm missing something.
>

nsv stands for number of separate visits, where a visit is defined as 
not being away from the hull for 12 hours or more. So the hull where 
nsv=22 doesn't mean the individual visited 22 times during one 
intervisit gap period, but rather it was there and left for more than 12 
hours and then came back, 22 times.

nsv values will of course be integer values. Those ranges you show I 
presume are from the plot legend, which R computes by taking the range 
of values and chopping it up into equal intervals. But the nsv values 
themselves should be all integers

> It is the same for the mean duration of visit. This means the mean 
> number of records taken of an individual during one visit to the hull, 
> right? But the output gives me
>
> 1.30 -- 11.56
>
> 11.56 -- 21.82 and so on up to 52.60.
>
> This cannot mean the bird stayed in this hull for 52 records. My GPS 
> interval is one hour and the transmitters are shut down during the 
> night to save energy, so they don't record over night. Maybe I have to 
> keep that in mind?
>

A hull where the mnlv=52 means the animal was within the hull for 52 
locations during at least one visit, where a visit again is defined by a 
period of separation. Hence that "one visit" could theoretically go on 
for several weeks, if for example the individual left and returned every 
11 hours like clockwork, it would all be considered one visit because 
your inter-visit period is 12 hours. That of course is very unlikely, 
more probably the hull where mnlv=52 could also contain a bunch of 
closely spaced locations, perhaps a site where it stayed for a long time 
or returned at intervals shorter than your ivg value, etc. The tip sheet 
on the website illustrates how you can investigate the time use metrics 
of individual hulls.

> I tried to send you a sample image for illustrationbut it seems to be 
> too big to be sent.
>
> I hope my explanation is understandable. I'd be very grateful for some 
> advice.
>
> Thank you and best wishes,
>
> Julia
>
>

Hope this helps. Let me know what other questions you come across.

>
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