[AniMov] BBMM questions: Sig2 and missing locations

Andrea Maxie andrea.maxie at gmail.com
Thu Jan 15 18:09:52 CET 2009


Hello, 

I am using the BBMM in adehabitat to to analyze GPS collar data and have two
questions that I'm hoping someone can help me out with.  I am pretty new to
R and adehabitat and would very much appreciate any insight anyone can offer
(and hopefully these questions are not too rudimentary).  My concerns are as
follows:

1)  As I understand from Horne et al. 2007, Sig2 is the standard deviation
of location error.  However, I have used data from stationary collars to
estimate location error and find that the data conforms to a bivariate
distribution (either by normal or Laplace distributions, see McKenzie et al.
2008, Environ Ecol Stat [Online]), rather than a simple normal distribution. 
By log-transforming the data, it is possible to normalize this distribution
and obtain sd values, but I wanted to verify that that is an appropriate
method for obtaining the required standard devitation value for the BBMM.

2)  I am hoping to get some clarification regarding the ltraj function and
inclusion of missed fixes in the data set for the purpose of using the BBMM. 
More specifically, will the home range and UD estimation be affected by the
ommission of missed fixes from the dataset.  Before deciding on using the
BBMM, I had removed missed fixes from my data set, and so I did some initial
coarse-scale comparisons against data that included the missed locations.  I
didn't find noticeable differences in the UDs, and continued with analysis,
but perhaps I made this decision with haste.  I am wondering if it is
necessary to reinsert the missed locations in the data set and redo the
analysis.

Thanks so much for your help.

Andrea

Andrea Maxie
M.Sc. Candidate
Trent University
Peterborough, Ontario
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