I have attached BAS geolocators (Biotrack - ML6540) on barn swallows breeding in Spain. In every light record (from July to March), I see many shading events at the end of the data (about 7-10 days). I am using the package BAStag, but I see too many shading events at this period to hand-edit these twilights. So I think the best option is to drop off this last records.
I think the biological meaning of these extensive shading events is the beguining of the nesting period at the breeding sites, i.e. birds spend nights at their nests.
However, I have some tracks in which the extensive shading events still occurr during migration (i.e. in the middle of the Sahara desert), a few days before arriving back to Spain. Thus I wonder if these shading events indicate indeed the beguining of nesting, and maybe because the tag surface become less transparent, the last estimated positions are predicted in the middle of the desert rather than in the breeding area.
So I do not know what is more correct: to set "known.last=" as either TRUE or FALSE. If I set TRUE, the last location appears in Morocco (closer to Spain), but the migratory track and winter areas seem more erratic. Furthermore the "plot_lon_lat", cannot estimate confidence intervals for the last days of records.
I know that one option can be to do a second calibration period back in the breeding areas. However I tried this already and because of the extensive shading events in this period, the final result is completely noisy and erratic. Maybe the best would be to do a roof top post-calibration period in a know location, but I think many of my tags do not have more battery. Does anyone have a better idea? I can provide screenshots of the results if someone wants to help.
Thank you very much in advance,