I am using SECR for my master thesis and it has been very helpful so far. I have however run into some problems and I was hoping that you (or someone else) could provide me with help. I am doing a camera trap study on African civets and I would like to estimate the density of African civets in the area. I am using secr 4.6.6 in R 4.2.3 on Windows 10. My dataset is unfortunately quite limited (44 observations of 3 individuals on 14 out of 20 camera traps).
When fitting the null model, there was too little data to determine the starting values, so I set these manually (D = 0.00001, g0 = 0.1, sigma = 1270.699). The density output I got for a mask with buffer width of 4*sigma seems reasonable. However, when I increase the mask size, the density becomes smaller. This seems odd to me, because making the mask too large should not noticeably affect the final estimate right?
When I try to fit the models for learned responses, I run into a problem. The learned response model (b) runs fine but it yields the exact same density as the null model. When trying to run the detector-specific learned response model (bk) I get an error:
- Code: Select all
civet.fit.bk <- secr.fit(civet_CH,
+ mask = clippedmask.civet,
+ start = list(D=0.00001, lambda0 = 0.1, sigma = 1270.699),
+ model = g0 ~ bk)
Checking data
Preparing detection design matrices
Error in aperm.default(temp, c(2, 1, 3)) :
'perm' is of wrong length 3 (!= 2)
Lastly, when displaying the AIC-values, I get values for AIC but I get NA for AICc, dAICc and AICcwt:
- Code: Select all
model detectfn npar logLik AIC AICc dAICc AICcwt
null D~1 g0~1 sigma~1 halfnormal 3 -77.53938 161.079 NA NA NA
b D~1 g0~b sigma~1 halfnormal 4 -77.53938 163.079 NA NA NA
I wonder if there is an easy fix for these problems, or are some of them the result of my very small dataset? Any help would be greatly appreciated. I have already searched for answers in the forum but to no avail. If you have time I could also send you my script and data, just let me know. Thanks a lot in advance!
Kind regards,
Luuk