discussion / Camera Traps  / 10 November 2016

Remote Camera Data Processing - Counting Individual Animals?

Hi Everyone,

I just thought to put the question out there to all of you using remote cameras to see if there is a common way of processing the photos collected from remote cameras. in particular, the time frame given when counting individual animals. EG: I have a fox captured in 3 photos, it leaves the camera frame for 30 seconds and then comes back into frame. How many times this fox is counted depends on the time frame decided on. Is that counted as 1 individual fox or 2?

I would love to hear about the time frame people use and how they have come up with that number. I am yet to find a paper that discusses this.

I have currently have 36 cameras in a 5x5km grid and I am collecting camera data to get an occupancy rate of feral species It would be great to have reasoning behind the time frame decision.

Thanks in advance


Hi Kate, in our studies we use the so called "independent events". In case we are 100% sure that within 5 minutes the same individual is going in or our of the frame (you should go through the images to be sure of that), we count this as one independent event (teh rest of photos are not counted anymore) and we work with this for our capture and occupancy analyses. We use modified version of CameraBase sotware which simpifies the recognition of the independent events.

My colleague Stu Newson at BTO faces a similar problem with acoustic detection of bats triggering an acoustic monitoring device. He's currently trying to figure out ways to statistically account for the same individual triggering the device multiple times in succession, in order to be able to make a robust estimate of abundance.

Consider what an occupancy study is trying to acheive. Also seems like you need to clearly define a session. I suggest you could estimate the minimum time it would take an individual to move across the study area between every possible cell combination. then using this list of travel times, calculate a simple lower 95% CI to use as cutoff.

Hi Kate, It all depends on the specie and data set accuracy you are trying to collect. If you are purely documenting frequency of visits, this is straight forward. However, if you are recording numbers then further analysis of photos may be needed. Some animals like foxes have distinctive marks or shapes, whilst smaller mammals can be a lot harder. If this is impossible, then a time limit should be defined across all camera traps. From all the papers I have read and projects we have worked with, there doesn’t seem to be clear standard. Hope this helps. Mike - handykam