Camera trapping foxes – can you identify individuals?
With the iWild North Wales project well underway and 3 sites already ticked off, the NatureSpy camera traps have captured a number of foxes already. But is it possible for us to tell the difference between individual foxes using camera traps, and even get reliable population estimates?
Gathering Grounds in Flintshire was not only a great spot for badgers to hang out, but also foxes. This tiny park, nestled between housing estates, gave us quite a few records of the orange carnivore. However – can we tell the difference between them, and maybe say how many there are using the park? Watch the video below and see how many you can count…
Click for video
As you can see, we can definitely say that there are more than 2. We have ‘Half-tail’, ‘Crooked-back’, and at least one more – but with no distinguishing features for us to easily tell them apart.
Of course, this has been more thoroughly tested before. The first was when Sarmento et al (2010) looked at red foxes in Serra da Malcata, Portugal, as it was a potential Iberian lynx release site. Because of the disease risk that foxes present to the Iberian lynx, having a good estimate of fox population size before any reintroductions took place was very important.
The most important areas for individual recognition that they looked for were skin patterns on the lower limbs, the general size and shape of the fox and the tail. They had an ace up their sleeves too though – from 1994 to 2001, they physically captured, weighed and photographed 125 foxes in the area and used that to help them identify the foxes they captured with the camera traps a between 2005 and 2007.
Is it possible to individually identify this fox, just from a camera trap video?
Sarmento et al were able to build a population estimate of between 53 and 67 foxes in the area. Great, right?
Well not quite. Doubt was cast over the validity of assessing the photographs, and whether individual recognition was truly possible.
Güthlin et al (2013) looked at whether it was really possible to reliably recognise individual foxes using camera trapping. They sent photographs of foxes from camera traps to 10 experts from around the world, and asked them to count how many foxes there were in total.
Unfortunately, the response wasn’t great. The estimated number of foxes from the photos varied from 4 to 23 individuals, and 50% of photographs that the experts thought were the same individual were actually foxes from completely different areas. There was also very little agreement between the experts on which photographs were the same individual foxes.
So, unless foxes have very clear and distinct markings (a missing tail for example!), it looks like identifying them individually may just be a step too far from camera trappers…