segmenting tracks, variograms

[Michaela A Kratofil]

Hi Chris/group,

I'm working with tag data from a couple of dolphins and have a few questions regarding segmentation and averaging subsequent UDs. Both animals had clustered/resident movements in one area, then moved to a another area for ~2-3 weeks, and then back to the first area. Based on the variograms (see attached "originals"), we segmented the data for each into three different segments to capture each behavior/range pattern and then average these segment specific UDs with mean(). 

I attached the variograms for the segmented tracks for each individual. The second segment for each is more of a "dispersal/exploration" type movement, which I suspect is why there isn't much of an asymptote. These aren't massive exploratory phases: both dolphins remain on the West Florida Shelf for the entirety of their tracking period (although this is obviously a large area). 

My first question is whether we should be averaging the segment-specific UDs for all segments (or only 1 and 3, which are more "range resident")? And any other thoughts on these variograms?

My other question is whether there is an appropriate reference/paper for this process of segmenting tracks and averaging UDs? Just wondering how to cite this process in our methods.

Thank you!

Michaela

[Christen Fleming]

Hi Michaela,

1. It depends on what range you want to estimate, in terms of their associated behaviors. If you include all, the dispersal/exporatory variograms don't look that bad. The data do appear to be irregular (I assume from fixes at the surface). You might tweak the dt argument and try fast=FALSE to see if you can improve the visual quality of the variograms, but that doesn't impact the model fitting.
2. I did not publish this specific method, and if anyone is interested in leading such a publication I would support that.

Best,

Chris

[Michaela A Kratofil]

Great, thanks so much Chris! 

I have two other questions:

1. For these two individuals (Bill, Ken), we will use mean() to get the individual-level UDs for plotting and reporting individual-level estimates. We also have several other tagged dolphins and will be using mean() across all individual UDs to get an average for the species. Should I mean() on all individuals plus Bill and Ken's three segmented UDs or is there an easy way to do all individuals plus Bill and Ken's single mean UD (if that makes sense)?

2. My understanding is that if we run akde() on a list of individuals (telemetry and movement model objects), all individuals will have a UD estimated on the same grid. However, when I plot any combination of different individuals (that were run together in akde()), it seems that they have different grids (see attached example). Just wondering if this is supposed to happen or if there is a common grid that is easily accessible from the resulting akde() output?

Thank you!

Michaela