Daily AKDE with different units

[Yana Korneeva]

Hello everyone,

I’m new to the ctmm world, so please excuse me if my question sounds basic. I'm currently working with GPS data from Kentish plovers in Cádiz (southern Spain).

The GPS devices do not provide fixes at uniform intervals (they range between ~5 minutes and 2 hours depending on battery state). To standardize the data, I interpolate locations to 1-hour intervals, so that I have about 24 points per bird per day. My goal is to estimate daily home ranges using AKDE so I can perform GLMM to compare between sites or periods.

So far, the workflow makes sense and the daily AKDE areas are in line with previous KDE results. However, I’ve encountered two issues:

1. Units in AKDE summaries
   When I run summary(akde) for each daily estimate, I sometimes get areas in hectares, sometimes in square kilometers, and occasionally even in square meters.

   • Why does this happen?

   • Is it related to the projection that ctmm assigns automatically in each daily dataset?

   • Is there a way to force all AKDE outputs to use the same units (e.g., hectares or km²) from the beginning, instead of detecting and converting later?

2. Interpolation vs. wAKDE
   I know that wAKDE can handle irregular sampling, but it is computationally heavy and takes much longer to run. That’s why I opted for interpolation to 1-hour intervals.

   • Is this interpolation approach appropriate, or would you recommend always using wAKDE?

   • Is ~24 points per day enough to obtain reliable daily AKDE estimates?

Any advice on best practices for this type of daily home range analysis would be greatly appreciated.

Thanks a lot in advance!