March 3, 2009 -- Ryan M. Leahy is the Lead Bear Technician at California's Yosemite National Park. As such, it is his job to manage the balance between a healthy bear population and human safety. Earlier this winter, amid unusually high temperatures in the Yosemite Valley, Discovery News correspondent Eric Bland sat down with Leahy to talk about the wonders of hibernation and the perils of incautious park visitors.
Discovery News: Are the temperatures this winter affecting the bears at all, or are they hibernating comfortably?
Ryan Leahy: With such warm temperatures, a number of bears never went into hibernation. Some of the bears have been active, but we haven't had too many issues.
DN: Why are the bears waking up?
Leahy: Winter dormancy for black bears is dependent on food availability and not much else. Right now the ground is uncovered, and there are still a lot of live oak acorns that are a good food source for the bears, so they can continue to forage here in the Valley.
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The pregnant sows go into dens regardless of food availability because they give birth to pretty helpless young. The den acts like an external womb to keep them warm and safe while they develop.
DN: So when do the sows give birth?
Leahy: The sows typically give birth in the last week of January or the first week in February. Usually a litter has between one and five cubs, with two being the most common. They are about the size of a Pepsi can and weigh less than a pound. They will be blind, unable to hear or smell, won't have any teeth, and have very fine fur. They will be very weak but able to nurse, and that's about all they do for the first eight weeks. They are pretty helpless little units.
DN: With some of the bears active, what kind of management activities are going on in the Valley now?
Leahy: Right now we are periodically trapping to identify bears in some of the housing areas, but other than that, we are mostly focused on office work..
DN: When will things pick up again?
Leahy: It depends on when food becomes available, but usually in late March or April the bears will emerge again and be extremely hungry. Bears are constantly hungry and in search of food, but in the spring and the fall they are desperately hungry.
During the winter a sow can lose as much as one-third of her body weight, so she will be looking for lots of shoots of fresh grass, all kinds of green vegetation. Black bears are omnivorous, and 85 percent of their diet is vegetation, which makes sense, since vegetation can't run away from you.
DN: That raises another issue -- humans bringing food into the park. How big of a problem is that?
Leahy: The biggest problem we face is improper storage of human food...It's imperative that bears don't become conditioned to human food and habituated to human presence, because as they grow more comfortable around people they lose their natural fear of us. Then they become bolder and start to change their habits.
Bears are usually active during the day, but they start to enter campgrounds at night because they feel safer under the cover of darkness...Like any intelligent animal, they think economically. They could walk around for eight hours searching for grass, grubs, or other food, or they can wait until night, sneak into a campground, and steal an improperly stored cooler that has much more calories without having to expend much energy to obtain it.
DN: So how do you deter bears from obtaining human food?
Leahy: First and foremost are our efforts to bear-proof Yosemite's developed areas...We also employ several levels of negative conditioning on bears, which is the use of negative stimuli to change an animal's behavior. The first level is yelling and chasing. Bears are supposed to be afraid of people, which makes sense because we have historically been the dominant animal. Most of the time, that works pretty well.
The highest level of negative conditioning is the projectile route. This is a combination of a negative physical stimulus that is associated with human presence, which makes bears more afraid of people. This involves highly trained personnel firing less-than-lethal projectiles at the animal's rump, which is much more effective than merely chasing them...These methods are only utilized if there is a safe shot, otherwise we don't even consider it.
DN: How do you find the bears in the first place so you can deter them?
Leahy: As far as monitoring systems go, in the early 2000s, the National Wildlife Research Center in Fort Collins, Colorado, developed the Monitoring Box Program to be used here in Yosemite.
Usually if a bear has been entering developed areas, we will trap it, mark it and fit the animal with a radio collar. We have five monitoring boxes set up around established campgrounds, and the radio frequency of every collared bear is entered into one of the receiver boxes. The boxes create a radio perimeter around the campground, and if a bear stays for more than a minute inside that perimeter, the system will call us on the radio and say "Bear in Upper Pines Campground," for example.
DN: What happens if you use all those forms of negative conditioning and a bear just won't stay away? The phrase I've heard other wildlife managers use before is, "a fed bear is a dead bear." Is there any truth to that?
Leahy: Yes, that's how we try to convey how important it is for the public to understand that a bear obtaining human food is the worst thing that can happen for them.
Here in Yosemite we do everything possible to return a bear to natural behavior. We trap them to properly identify them, collar them to help us negatively condition them out of developed areas, and in some cases even move them out of the area.
Unfortunately, when these measures don't work and a bear clearly threatens humans, we have to destroy that animal. That's the worst part of my job, the absolute worst. It's never the bear's fault, it's always caused by human carelessness. We're all haunted by dead bears, which make us work all the harder to keep Yosemite's bears truly wild.
DN: If that's the worst part of your job, what's the best part?
Leahy: Wow. That's a tough question because I can honestly say that I love my job. In this line of work I am always inspired to see how much park visitors enjoy viewing wildlife in a natural setting, and that reminds me why I chose this career...I have to say that without a doubt the best part of my job is when I know that we have made a difference in keeping an animal wild.
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