During the past few years, San Diego's rural tree squirrel population has nearly reached extinction. Their population is apparently coming back, even though few people seem to know exactly why they died off in the first place.
Scott Treemore, 37, is a research assistant at the Natural History Museum in Balboa Park. He has been studying squirrels for the last four years and monitoring local squirrel populations. "You'll find arboreal [tree] squirrels mostly in the coniferous forests in the backcountry and some of the local inland areas, particularly at higher elevations. It's the western gray squirrel and it's the common squirrel that people see that lives in the trees. Their populations don't normally fluctuate, but they were hit with a virus three years ago, and their population crashed. Now they're slowly coming back. I don't think it's a boom. They reproduce quickly, but it's going to take a while for them to move into new areas. I can't give you a number for the population -- you would have to do relative densities, and the relative density has increased over the last six months, but it's a very slow increase. It will take several years for them to get back to normal, about as long as it took for them to crash. The plague is mostly associated with ground squirrels."
Treemore opens a locker in a corridor on the third floor of the museum. He pulls open a drawer that has several stiff, dead squirrels laid out as scientific specimens. He explains how the gray squirrel likes to eat nuts and fruit, which can cause problems for local farmers and orchard owners. (Two Julian orchards were contacted, and both said that the tree squirrels never gave them any problems.)
"It's mostly the fruit trees out in that area. They are nut-and-seed eaters too. But I think that, legally, on your own property, you can trap them. Some people use the 'have-a-heart' traps, where they can trap them and relocate them somewhere else."
Laura Itogawa is the supervising ranger for Cuyamaca Rancho State Park and a Julian resident. Itogawa says that the squirrels are just beginning to reappear. "There was a virus that nearly killed them all off. It was an upper-respiratory infection that pretty much took out all the gray tree squirrels and rabbits. I lost two bunnies to it. About three years ago, I began to start seeing gray squirrels again up at the [Stonewall] mine, maybe two or three. I saw one at Green Valley last year, but that's about as far back as I've seen them. They're trying to make a comeback. Before, they were all over Julian, and I used to see them in my yard, but I still haven't seen one there since the infection came through. It was more than 90 percent that died. We went from having them everywhere to having none. The way I understand it, it was airborne, because my rabbits were in a cage."
Bill Goddard, a volunteer ranger at the Mount Laguna station, says that the tree squirrels were infected with a disease called snuffles. "I haven't seen any for quite some time." His wife, Phyllis, agrees. "Every so many years, they get the plague or something, and we don't have them around for quite a while. Then they gradually come back. I think last year I only saw a couple of the gray tree squirrels. We have ground squirrels aplenty!"
Another ranger at William Heise County Park, near Julian (who asked not to be named), said that there has been a tremendous drop in the population of tree and ground squirrels. "I'd heard that there was a disease that was particular to them, kind of like AIDS. I've seen one or two tree squirrels recently, and I'm glad to see them coming back. They're so beautiful."
Chris Wiersema is the squirrel team leader for Project Wildlife, a nonprofit group located on Sherman Street, near the Humane Society, devoted to rescuing and releasing endangered wildlife. "We've been seeing them sporadically over the last couple of years here and there, but no great numbers. I've heard that they are on the rebound. But we only see the ones who are injured or orphans, not the healthy animals. We see very few tree squirrels at all. The population is even down in Balboa Park. I know they've seen a few more in the mountains. The few we've caught down here we've released in the Julian-Cuyamaca area, hoping they would build. I know they've been seeing them out at the lake."
Dr. Jim Lang, the senior vector ecologist for San Diego County Vector Control, says that there has never been any virus. "I know that it's been a lot warmer the last couple of years and the plague hit some animals, but we've never had a die-off of squirrels caused by plague in the mountains. Tree squirrels are not affected by plague at all. I know that they're affected by mites, which can cause dermatitis and kill them that way. Sometimes these gray squirrels can get into garbage cans and get infected with salmonella, and that can kill them also. There was a big die-off of gray squirrels about five years ago in the Palomar and Pine Hills area near Julian, but I don't know what caused it. Perhaps the county veterinarian has had some squirrels come in that had died and examined them."
Dr. Al Guajarda is a public health veterinarian for the County of San Diego. "There hasn't been any virus diagnosed in any squirrels. I know that vector control will go out and tranquilize squirrels and test them to see if they have any exposure to plague by checking for antibodies. I do remember that in Alpine some squirrels had a bacterial infection called pasteurella, and it seemed like it was affecting the respiratory infection. It also affected their skin. We never knew why they caught this infection, and it did affect a certain amount of squirrels about four or five years ago. I don't think it went to wiping out most of the population.