Wednesday, 25 Jul 2001
MINERAL, Calif.
The western half of Lassen Volcanic National Park is probably the shattered rim of an ancient giant volcano that exploded thousands of years ago, showering debris across much of Northern California. Today the area is all rocky ridges and steep slopes. Mountain hemlocks and tangled whitebark pines dot the jagged mountain cliffs, while steam vents and boiling mudpots line the valleys. A single, two-lane road snakes its way from the park's southwest entrance, at about 6,000 feet, up along the ridges to the foot of Mount Lassen, at 8,500 feet, and then back down to the dense evergreen forest on the other side.
Part of our research project involves following a handful of Sierra Nevada red foxes so we can learn how they live in this rugged environment. The phrase "breathtaking landscape" takes on new meaning if you're on foot chasing after a mountain red fox as it hunts its prey. The foxes are active mostly at night, so chasing them around as they conduct their business is no simple undertaking even without the cliffs and valleys.
Me, conducting telemetry in Lassen Park.
Photo: Tom Rickman, US Forest Service.
Instead of following the foxes by sight, we track them by using radio telemetry. Every red fox in our study has a powerful radio-transmitter collar around its neck. Each fox transmits on its own radio channel, so we can dial in any particular fox on our hand-held receivers. We have hand-held antennas that look like tiny old-fashioned TV aerials, and the radio signal is loudest when we point the antenna directly toward the fox we're tuned to. By going to several different places in the course of an afternoon and noting the strength and direction of the radio signal at each place, we can calculate an approximate location for that fox without ever seeing it or disturbing its activities. We can also track them from a small airplane equipped with antennas on its wings.
We check in on our foxes several times a week, usually on Mondays, Wednesdays, and Fridays, varying among morning, afternoon, and night. Over the course of a season, we calculate dozens of locations for each fox, slowly building up a picture of how each animal uses the landscape. The process works well and has been a critically important tool for wildlife biologists for the past three decades.
The real trick is getting the radio collars on the foxes in the first place. We catch the foxes using a wire cage trap the size of a dorm mini-fridge. We set out a dozen or so of these cage traps throughout Lassen Park and the Lassen National Forest, baiting each one with a chicken leg and some scent lure. The foxes are not abysmally stupid, so they avoid these traps like the plague. But eventually hunger and curiosity overwhelm a fox's judgment, and it darts inside the trap, grabs the bait, and runs away. The trap doesn't catch the fox because we wire the trap door open for the first few weeks. This lets the fox overcome its fear of this odd contraption that has suddenly appeared in its backyard.
Red fox avoiding capture in our box trap.
Photo: John Perrine.
After about two weeks, the fox learns that the contraption seems to have new chicken legs in it every night, free for the taking. Then we remove the wire that holds the trap door open, and, hopefully, the next morning we've caught a fox. It's a neat trick when it works, which is about two times out of 100. More often, we'll catch a pine marten or a skunk or something else unintended, or the bait will be stolen without catching anything at all. Or, we'll catch the same fox over and over, because it's happy to spend the night in our cage munching on a chicken leg.
Because these mountain red foxes haven't been studied since the 1930s, the rare occasions that we actually capture a new red fox generate a flurry of activity. We use a special handling bag to remove the fox from the cage, and then we give it a thorough medical exam to make sure it's not injured. We determine its sex and, for a female, whether she has recently reproduced. We weigh it and measure it and make notes about its teeth and its color patterns and anything else that seems relevant. We take some blood and a genetic sample, attach the radio collar and a numbered ear tag, and then set the fox free as quickly as possible.
Since the spring of 1998, we've caught a grand total of one male and four female red foxes. That's about a quarter of the number we had hoped to catch, but it's a starting point. Ironically, although the foxes seem abundant in the Lassen area compared to other places in the Cascades and Sierra Nevada mountains, they are still few and far between here.
We've tracked some of our foxes for several years, giving us great insight into how they use their habitat and respond to changes in the seasons. This information adds critical pieces to the puzzle of how we can ensure that these fascinating animals survive well into the future. On Friday, I'll summarize the picture that's beginning to emerge.
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