## Detection probability per night versus per session

questions concerning analysis/theory using program PRESENCE

### Detection probability per night versus per session

Hi,
I am trying to better understand if the detection probability from single-season occupancy models is per night or per session?

Some context:
I did an analysis of camera data where the cameras were deployed for three nights (nocturnal species of interest) at all stations, for one sampling session. I repeated this each season (4 total) across the year. So each station has four detection histories, one for each season. I then analyzed the data and obtained a detection probability (that varied by season). My question is, if the detection probability, say for summer was given at .87, is that the probability of detecting the species across a three night deployment, or the probability of detecting the species each night of deployment?

I am trying to estimate the probability of not detecting the species if it was present at a site from one session (3 nights). Reviewing Mackenzie et al (2018) book, the example (ch4, blue-ridge salamanders) was conducted where each survey was one day, and there were five surveys, so they probability of not detecting if it was present is : (1-p)^k, where k = 5 for five surveys.

So my question is, if my survey session were 3 nights, then the detection probability I have obtained (0.87) is the probability of detecting the species should it be present for each night of camera deployment? So my probability of not detecting if it was present for on session would be : (1-.87)^3? . Likewise if it was not detected at a station for all four seasons, the probability of non detection if present would be (1-pSummer)^3(1-pWinter)^3(1-pSpring)^3(1-pFall)^3

Jaranlanae

Posts: 4
Joined: Tue Mar 29, 2022 3:16 pm

### Re: Detection probability per night versus per session

Yes, the detection estimate (p) is the probability of detecting the species in a sampling occasion (night in your case). So, you have the correct formula for non-detection in a 3-night session, (1-p)^3.

The formula for non-detection over the 4 seasons, (1-p\$summer)^3 * (1-p\$winter)^3 * (1-p\$spring)^3 * (1-p\$fall)^3, is correct if the site is occupied all 4 seasons. However, if occupancy changes between seasons, then some sites may not be occupied in seasons 2, 3 and 4 which were occupied in season 1. For sites which were occupied only in season 1, the probability of non-detection over 4 seasons would simply be, (1-p\$summer)^3, since there is a 100% chance of non-detection in seasons 2,3 and 4.
jhines

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Joined: Fri May 16, 2003 9:24 am
Location: Laurel, MD, USA

### Re: Detection probability per night versus per session

Thank you for your insight and help!
Jaranlanae

Posts: 4
Joined: Tue Mar 29, 2022 3:16 pm