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 jalapeño 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.

Haldane and Hybrid Bears

Haldane's* Rule:

When in the offspring of two different animal races one sex is absent, rare, or sterile, that sex is the heterozygous (heterogametic) sex.

This rule is almost universally true (see table**) and is supported by the observations that among hybrids such as ligers, zonkeys and mules the males (XY) are all sterile while females (XX) may be fertile (though often poorly so, due to mismatched chromosome numbers, discussed briefly here). The reverse observation - sterile females - is true in species where the male is the homogametic sex such as birds and butterflies. Hypotheses explaining the genetic basis of Haldane's Rule and its challenges are explained nicely here.

Recently, a new fertile hybrid was discovered. The grizzly-polar bear hybrid has been seen before, as discussed here, and with changing habitats and more grizzly-polar bear encounters we'll likely see more. The Toronto Star is reporting the first offspring of a hybrid bear.

Researchers in the Northwest Territories say they may have found the first recorded offspring of a hybrid female polar-grizzly bear in the wild. [...] Officials with the territorial government say those test showed that the dead bear was the offspring of another hybrid bear — a female polar-grizzly mix who had mated with a male grizzly.

Given Haldane's Rule, that the hybrid parent was female isn't surprising, but it remains to be seen whether the males are sterile or if this becomes the first mammalian exception.

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*In addition to being one of the founders of population genetics, Haldane also wrote poetry about rectal cancer, a disease he succumbed to in 1964.

**Table source: Nature 355, 511-515 (1992). Ref. 41 refers to Coyne, J.A. and Orr, H.A. in Speciation and its Consequences (eds Ott, D. and Endler, J.) 180-207 (Sinauer, Sunderland, Massachusetts. 1989)

Bear Fight!

Yesterday's Globe and Mail reports on research indicating that grizzly populations are starting to migrate into polar bear territory. This crossing has occurred in the past, as evidenced by the 2006 discovery of a polar-grizzly hybrid, but is becoming more frequent. This, of course, has re-ignited the age-old debate over which would win in a fight. From the article:

Dr. Rockwell, dedicated academic that he is, has pondered such a tilt at length. He believes the two bears would most likely come into contact around the peat banks that make the only decent denning ground within Wapusk National Park. Because polar bears only den when they're giving birth, the most possible scenario would see a weakened female take on a grizzly of either sex.

“If it's a fight between a 1,200-pound male polar bear and a 600-pound grizzly, I think we know who would win,” Dr. Rockwell said. “But in this likeliest of cases, it's debatable. There are actually reports in the literature where grizzlies have killed denning polar bear females.”

Naturally, non-experts are weighing in as well:

“Polar bears are used to eating seals which are easy prey, while grizzlys [sic] hunt lions,” wrote one dubiously informed member of a Yahoo message board.

At boxingforum.com, members have devoted 19 pages worth of comments to the prospective fight.

Bear baiting may not be dead after all.

Bears, Sharks and Strippers

Brick Tamland [opposing women in the newsroom]: I read somewhere their periods attract bears. Bears can smell the menstruation.
Brian Fantana: Well, that's just great. You hear that, Ed? Bears. Now you're putting the whole station in jeopardy.

That little nugget of wisdom comes from the movie Anchorman, but that's not its source. It's often repeated, and likely stems from a bear attack in 1967 that left two women dead and many people speculating that the bears were attracted by menstrual odors. Is there any truth to that claim?

Research has been done on the subject. In 1991, a study was done showing that black bears are uninterested in human menstrual odors. This was done with a series of experiments involving either used tampons or menstruating women in close proximity to the bears. The results showed no preference of the bears for tampons over garbage or feed. There was no preference for used tampons over unused tampons or those soaked with non-menstrual human blood, and no difference in interest with the lower torso of menstruating versus non-menstruating women. In all cases menstrual odors were virtually ignored. For grizzly bears, no scientific studies have been done, but a retrospective analysis of grizzly bear attacks on humans showed that there was no evidence linking menstruation to the attacks.

One place where an attraction to human menstruation may be true is in the polar bear population. In a 1983 study, polar bears both in captivity and in the wild showed a preference for food scent samples or used tampons over unused tampons or non-menstrual blood suggesting that polar bears are attracted to menstrual odors. A brief summary of these studies has been published by the bear management office of Yellowstone National park and can be read here (pdf).

Overall, the evidence indicates that unless you're heading pretty far north you don't have to worry about menstruation attracting bears. The Museum of Menstruation and Women's Health backs up that claim. What if you're into SCUBA-diving instead of hiking? Sharks are notorious for their attraction to blood in the water. The Museum of Menstruation has something to say about that as well: "many women fear that this discharge may attract sharks. The truth is that women divers are attacked by sharks less often than men are." However, there could be a number of reasons for this difference, and whether sharks are attracted to menstrual bleeding remains inconclusive as no controlled studies have been done. There are arguments to be made for both sides, as discussed here, but the consensus among divers, at least, is not to worry about it.

So bears are indifferent to menstruation and we're unsure about sharks, but what about people? There are behavioural cues, but no solid data regarding pheromones. Other phases of the menstrual cycle are better studied, including the time of maximum fertility just before ovulation. Many studies have shown that women at this point in their cycle, 'hidden-estrus', appear more attractive to men by a number of different metrics. (Some studies were mixed-sex and women found them more attractive as well!) This can be accompanied by other behaviours, such as men being more attentive or protective of their partners. The effects of 'hidden-estrus' signals on male behaviour is highlighted in this recent paper in Evolution and Human Behavior. In this study, 18 strippers reported their tips and menstrual cycle over a period of 60 days. It was found that among normally cycling strippers, peak tip earnings occurred during 'estrus' compared to the luteal phase which, in turn, were higher than during menstruation. This difference disappeared among strippers taking birth control pills. A deeper discussion of the paper can be found over at Pure Pedantry. For people who may not be familiar about the inner workings of a strip club (or, as the authors put it, "Because academics may be unfamiliar with the gentlemen's club subculture...") the paper even includes some background on the US stripping industry that alone is worth the read. Despite it's inherent humour value, this study could be a jumping off point for some interesting discussions about human evolution and behaviour. Have humans actually lost the 'estrus' phase, or is it just better hidden than in animals? What are the evolutionary advantages? Or it could just be an excuse to do more science in a strip club.