Tuesday, April 23, 2013

Bear Spray

Where I'm living black bears are quite commonly seen around town. While I have yet to hear of a really bad bear encounter many bears are destroyed every year for getting too familiar with town. Most people here merely avoid them when they see them. Alternatively, aggressive responses to threatening bear encounters include firearms and pepper spray. While obtaining a firearm requires getting a firearms license and many restrictions, getting bear spray is as simple as purchasing some from Canadian Tire.

So what is bear pepper spray and does it work?

The active ingredient in bear pepper spray is the same compound that makes some peppers spicy. This spicy compound is caspaicin. Bear spray is also known as capsicum deterrent since capsicum is the genus of plants that includes caspaicin containing peppers.

Capsicum plants have evolved production of caspaicin in order to deter mammals from consuming the fruit of the plant. When consumed capsaicin produces a strong burning sensation in the mouth. This burning sensation is experienced by most other mammals, and is real, at least according to your brain. Capsacin binds a cellular receptor that is also activated by temperatures exceeding 43 degrees Celcius. The receptor, transient receptor potential cation channel subfamily V member 1 (TRPV1), is responsible for communicating pain and has a role in temperature regulation. Evolutionary pressure has caused capsicum plants to produce capsaicin to reduce their consumption by mammals. Exposing seeds to the mammalian gut prevents capsicum seeds from germinating. Bird TRPV1 receptors do not respond to capsaicin and therefore capsicum plants and seeds are readily consumed by birds. The avian digestive system doesn't not destroy the ability of the seeds to germinate and therefore birds contribute to capsicum seed dispersal.

So if this is the same compound found in hot peppers and salsa are we not just giving the bear a bit of a spicy snack? The difference between tasty and bear repellent is concentration. Spicyness or capsaicin concentration is usually quantified by an antiquated unit of measurement called the Scoville unit. The Scoville Unit tries to be objective but ultimately relies on 5 tasters determining the dilution factor that produces a solution with no caspasin taste. So for some spicy perspective, while an average jalapeƱo pepper has about 3500 to 8000 Scoville units, bear pepper spray has about 3.3 million Scoville units.

So spraying a bear with 3.3 MScoville Units causes the animal spicy pain, but does it actually work? In other words, in the real world are there statistics to show that being armed with a canister of pressurized capsaicin reduces harm to you and/or the bear? An article from 2008 reports that in 20 years worth of bear encounters reported in Alaska, bear spray was effective in reducing the severity of the encounter 92% of the time, while firearms were only 67% effective. This is the kind of evidence, almost convincing enough, to justify taking my gun rack off my mountain bike.