They also prefer to dine on corn and garbage. So women, feel free to go hiking at any time of the month.
The death of two menstruating women attacked by grizzlies in Glacier National Park in 1967 apparently prompted the government to print brochures warning women to avoid bear country during periods of active menstruation.
Although some sites, like this one caution "women may want to avoid the backcountry during their menstrual period", there is little or no reason to be concerned about hiking during menstruation.
(SOURCE)The examination of factors surrounding hundreds of grizzly and black bear attacks produced neither evidence that supported a causal relation between human menstruation and attacks nor revealed any published records concerning black bear responses to menstrual blood. The U.S. Forest Service conducted a series of experiments (Rogers et al., 1991) which tested the responses of both male and female black bears to human menstrual odors. The first experiment involved the spin-cast introduction of 15 used tampons (in clusters of 5) to adult male black bears foraging in a garbage dump. Each presentation, therefore, gave the bears a choice between the garbage and tampons. If the bears ate (like they did the garbage), closely sniffed, or rolled on the tampons, then they were considered to have paid attention to the tampons. Of 22 presentations, the bears ignored the used tampons 20 times (twice casual sniffs were observed), effectively preferring the garbage in every instance. In a second experiment, seven bears feeding on piles of corn were offered groups of six used tampons. Six of the bears sniffed the tampons and then returned to their piles of corn. A yearling male tasted one of the tampons, quickly dropped it and returned to the corn.
A third experiment placed four used tampons, an unused tampon, a tampon soaked in non-menstrual human blood, and a tampon containing rendered beef fat in the middle of a heavily traveled bear path with the used tampons interspersed among the others. Ten out of ten bears ate only the tampons soaked in beef fat. In a fourth experiment, women on different days of their period accompanied and contacted bears who were accustomed to human interaction and were known to investigate attractive odors. Eleven encounters involved women wearing tampons and one crazy woman wearing clothing through which her menstrual blood was soaking. Of the twelve encounters with the women, the ten bears did not pay any attention to the lower torsos of the women. Another woman wearing external pads during two of her menstrual cycles hand-fed four female bears and walked within two meters of adult male bears during bear mating season and did not receive any attention. Rogers et al. (1991) concluded that the lack of interest of the bears to menstrual odors does not prove that such odors are never attractive to bears (similar experiments resulted in tampon feasts by polar bears lacking attractive buffets); however, menstrual odors essentially were ignored.
More references here, here, and here. Original inspiration from a friend who heard about this on a radio programme on CKLN.
More than you'll ever want to know about menstruation from the Museum of Menstruation.
