Applying PRESENCE to hunter survey data

[Tyler]

Hello,

I am interested in using PRESENCE, hunter survey data, and covariates (site and occasion-specific) to model the proportion of each sampling unit occupied by bobcats in a 24,000 km^2 study area. Hunter survey data can be identified to townships. Townships are oddly shaped, size ranges from 2 to 393 km^2, and N=259 comprise the study area. In 2009, 115 of 16,730 hunter outings detected bobcats in 76 of 210 surveyed townships. Hunters chose which townships to survey and we do not know where they hunted within each township or distance walked (we have duration of each outing). We suspect that hunters generally selected townships likely to contain bobcats (hunters and bobcats were pursuing deer). Can anyone offer guidance on dealing with irregularly-sized sites and lack of a probabilistic sampling scheme, or comment on the value of attempting this at all?

Thank you very much,

Tyler

[jhines]

Hi Tyler,

The irregular sizes of the sites can be handled with a site covariate, so bigger sites can have different occupancy than smaller sites (in a linear fashion). The non-random sampling is a bigger problem as your sample only represents sites which hunters have chosen. If you assume the occupancy and detection estimates are the same for surveyed and un-surveyed townships, I would expect the occupancy estimate to be biased high, since hunters probably aren't going to go to sites which have no chance of seeing the species.

So, your occupancy and detection estimates will only apply to surveyed townships and you won't be able to say anything about the un-surveyed townships.

Jim

[Tyler]

Jim,

That clears things up. Thank you for your input.

Tyler