Friday, June 8, 2007
Five months of Mossy Rock visitors
It's been seven months since I cabled the camera trap to a bay tree next to the mossy rock. Why have I left it there so long? The pumas are the reason. I thought they might return, and they did. But a lot of other animals passed by too.
Before I go any further, however, I have to confess that this was not a scientific experiment. If it was, I would have controlled my own impulses to attract animals to the site. On the contrary, my own flights of fancy introduced a lot of confounding variables -- like the different baits and lures I used to attract photographic subjects.
The camera has been in operation most of the time--164 days (or 5.4 months out of 7 months)--and it's still there. I lost a couple weeks of data due to downloading errors, and a few interruptions were due to battery failures and temporary dementia resulting from over-excitement. (The latter happens when I get pictures of pumas, and I forget to switch the mode from "View" to "Photo". You should see me cursing myself when I return a week later and find that the camera was in view mode.)
Back to the data. During the sampling period the camera took 588 pictures, 79% of which were images of 17 species of birds and mammals. Not a bad success rate.
Now let's start the drum roll and focus on the graph at the top of the page . . .
As you can see, the winner of the most commonly photographed animal is . . . . THE DEER MOUSE (huzzaaah)!
However, if I hadn't scattered sunflower on the rock I am not sure mice would have accounted for 45% of the photos. Sometime in February I got the bright idea that baiting deer mice would attract the screech owl, and I started to fantasize about photos of owls gripping deer mice.
Spotted skunk (29), wood rat (26), puma (24), and squirrel (24) were the next most commonly photographed species, followed by gray fox (19). All other species, including all the birds, were photographed from one to 8 times.
Camera traps are commonly used to inventory wildlife, and especially mammals. Plot a species accumulation curve and often you find that the number of species photographed rapidly increases at first, and then decreases.
In this case, 70% of the 17 species showed up in the first 58 days. But a long time must pass before you stop getting the occasional new species. You may think you know what's there, but sooner or later something new shows up. I know that opossums, coyotes, raccoons, long-tailed weasels, and otters occur in the area, but not one visited the mossy rock.
Camera traps are a useful inventory method, but they have their limitations. Some species are highly selective in their use of habitat, avoid strange objects such as cameras, or may only be attracted to special baits and lures. To photograph these species you have to know where and when to look, and how to attract them. If you are working in a unknown area, and don't know what to expect, you have to explore all habitats thoroughly.
Even then, you need to rely on a number of different methods, and consult with local people. They usually have a very good idea of what's around. I now consider myself one of them, and can tell you with confdence who visits the mossy rock.