Accounting for occasion-specific changes in sampling effort

[coba...@ucsc.edu]

Hi all,

I'm wondering how to incorporate animal captures during occasions where sampling was opportunistic and does not have associated effort/usage metrics. My data comes from noninvasive genetic sampling (snow tracking) that took place over 3 consecutive years (sessions) with 2 occasions each (beginning and end of winter). For these occasions, effort (km of snow tracking) is assigned to grid cells within the study area. However, I also have a third occasion for each session where sampling was opportunistic. I would like to vary the usage/effort by each occasion using non-binary usage (km of snow tracking).

Is there a way to incorporate this third occasion into a time-varying model (ie g0 ~ t or sigma ~ t)?

Would assigning all zeroes to this opportunistic occasion cause issues with interpreting model outcomes? When I do this, I get zeroes for the values for beta parameters for this occasion.

I appreciate any insight and help with this!

Best

Colby

[Murray Efford]

Zero effort (usage) is not what you mean. You could set some arbitrary usage value (perhaps the average of all others) for the third occasion and use a time (occasion) covariate to distinguish the first two occasions from the third, something like

secr.fit(ch, model = g0~tcov, timecov = c(1,1,2))

(tcov is the standard name for an unnamed timecov). This separates the effort-specific g0 of occasions 1-2 from the arbitrary g0 of occasion 3, hence marginally better than g0~t. Awkward to describe and interpret!

[Colby Anton]

Thanks Murray, that worked perfectly.