A year in Marin

Time to summarize a year of camera trapping in Marin County.

Our camera trapping beat in the redwoods, coastal scrub, and mixed deciduous woodlands, is home to about 28 species of land mammals and year-round or seasonal home of about 144 species of birds.

The goals were to carry out a simple recce of medium-size or meso-mammals and to provide the Audubon Canyon Ranch with the resulting photographs for their education program.

Cameras were set on trails, and we used a few scent lures only for the first few sets.

So most of the time the cameras monitored normal trail traffic.



1167 (92%) of the photos were of mammals, and the remainder of birds.

8% of the mammals were people (hikers and school kids).

The graph shows that the most commonly clicked subjects were black-tailed deer, brush rabbits, and western gray squirrels.

Of course some of these photos were repeated images of the same animals coming and going, or weaving on and off the trail.

But all the same, these are abundant species that feed the predators in the area.

We photographed 39% of the 28 mammal species known in the area and only 6% of the 144 species of birds recorded in the area.

That's not surprising.


We were not trying to survey birds, but even if that was the goal, camera traps are not the tool of choice.


If the goal had been a comprehensive survey of mammals we would have fallen far short of the mark.


The problem is this: some species, like bats, shrews, moles, and yes, shrew-moles just aren't very detectable by camera traps, unless you make special efforts.


If you take those mini-mammals out of the equation, we photographed 55% of the mammals known on the property.


Obvious omissions were the black-tailed jack rabbit, striped and spotted skunk, and mountain lion.


The absence of mountain lion photos is understandable, though one was seen in late spring and not far from a camera.


Certainly there is no shortage of lion food in the area.


But where are the skunks?


Road killed skunk has always been a common sight in Marin County, and normally they are highly detectable by camera trap.


Did an epidemic -- rabies, canine distemper or some other disease -- lay the skunks low?

Food for thought.


Another thought is that periodically compiling results is a good way to drive home a few messages.


First, sampling all habitats increases the chance of recording more species.


We covered one habitat intensively, but need to spend more time camera trapping coastal scrub and redwoods.


Second, camera traps are best at capturing medium to large mammals, and ground living small mammals like rodents.


We will have to work a bit more to find microhabitats and amke camera trap sets for shrews and shrew moles, and perhaps bats too.


Third, there is no fixed amount of time that will reveal all species in a given area detectable to camera traps.


Populations change. Mammals are subject to epizootic diseases that periodically reduce populations to very low levels, often over areas larger than the sampling areas biologists use for camera traps.


Fourth, the Marin experience proved that the longer you wait the better your chances of photographing something interesting.


It didn't take long to figure out that set 228 was in the core area of a bobcat's home range.


We monitored one short length of trail for 8 months, and were rewarded with photos of bobcat kittens, and a cat carrying a recently caught gopher snake and brush rabbit.


And finally, many thanks to Gwen Heistand and her staff for their interest and help.

2008 annual report

A few words to wrap up camera trapping in '08.

First, I expanded my home range, which means I made 75 camera trap sets in three states.

Most were in California (Butte, Napa, Yuba, San Mateo, and San Luis Obispo Counties), several were in New Mexico (Mora County), and one was in Virginia (Arlington County).

The yield was 2488 animal photos. The majority (2371 photos) were of  32 species of mammals. (I am not certain about my identifications of mice and shrews, so the species estimate is conservative.)



These statistics have nothing to do with relative abundance, and if anything, have more to do with the habitats I have chosen to set the cameras.

I added several new mammals to my species list: desert cottontail, white-throated wood rat, Douglas squirrel, Allen chipmunk, northern flying squirrel, Heermann's kangaroo rat, beaver, American marten, elk and feral pigs.

Bigfoot continues to elude and play tricks on me, like running in front of the camera and giving me blank images. I am convinced they have a sense of humor, but one of these days I am going to trick their butts.  

Two observations got me jumping: gray foxes carrying recently caught wood rats at Rich and my cams in Napa County, and black bears dragging nesting material into their den at the Wind River Ranch.

The 21 species of birds were incidentals. I wasn't looking for them.

It's hard to get good pictures of small birds with these cameras, and I just haven't spent enough looking for raptor roosts. 

Nonetheless, little birds just show up, and their variety makes camera trapping more interesting.

The bird thrills were the pileated woodpecker, blue grouse, and the bathing Cooper's hawk and screech owl.

My new MO was camera trapping with fellow codgers. This was the upshot of a little workshop with some old college buddies I did here a year ago.

As a result, Reno Taini reintroduced me to the wilds of the coast range in San Mateo county, while Rich Tenaza opened the gates to the Cleary Reserve in Napa County.  

Brian Miller led me to the bears den at the Wind River Ranch in New Mexico. I can't say enough to thank Brian and Carina for their hospitality to Dave Rentz and me last September.   

In June we visited Greg McMillan on his splendid ranch in San Luis Obispo County. Greg  treated us just like family. Not only did he cart us to the springs on his property to set cams, but he secured permission to camera trap on his neighbor's spread.  When we couldn't align our schedules he collected the cams and mailed them to me. I photographed more species there than any other locations. Thanks, Greg.

I also want to thank Etienne Benson, Mickie Enkoji, and Douglas Fox for three popular articles on my camera trapping activities. The articles generated food for thought about ethics and interpretation of animal behavior. 

Plus the publicity boosted blog readership. I'm self motivated when it comes to camera trapping, but I can't deny that its nice to hear from folks too.   

Thanks for your interest.

Several whacky new projects are cooking, so stay tuned. One of these days you will see the Sonoma Tree Mouse disporting itself on its arboreal midden of food scraps or a tree climbing mountain beaver pruning alder twigs in the high Sierra.