Monday, June 2, 2008

MALEVOLENT MOTHERS AND BRUIN BABYSITTING: PART 1

When sows nurse their young, they are placed in somewhat of a precarious position, having to recline on their back with back legs splayed forth. It turns out, some females will utilize groups of humans as a refuge as they engage in nursing. Photo by Scott W. Michael

“Hushai said moreover, "You know your father and his men, that they are mighty men, and they are fierce in their minds, like a bear robbed of her cubs in the field…” 2 Samuel 17:8

"Better to meet a bear robbed of her cubs than a fool in his folly." Proverbs 17:12

"I will meet them like a bear that is bereaved of her cubs, and will tear the covering of their heart." Hosea 13:8

The writers of old were well aware that it was not a good idea to threaten the young of a mother brown bear. Contemporary authors have rang the same warnings bells. If you read any guide on recreating in bear country, one of the ironclad rubrics is to never approach a grizzly sow with offspring. As we discussed in an earlier posting, mother grizzly is a product of her environment, which in the past, was not a very safe place to raise a family. So she will sometimes respond aggressively to a perceived threat - which people are, at least over some portions of the grizzly’s range.

Consider the case of Ann Quarterman and Christine Bialkowski described in the book Mark of the Grizzly. While this book is considered “bjorn porn” (bjorn is Norwegian for bear*) by many ursidophiles, the Quarterman and Bialkowski attack clearly demonstrates just how protective a mother bear can be. The two women were hiking in Glacier National Park, when they spotted a sow with two cubs of the year in tow some 300 meters away. The female, upon spotting the two hikers, immediately began charging toward them. The two girls jumped up and down and yelled hoping that the bear would recognize them as human and forestall her attack, but the sow kept coming. They finally ducked behind a rise so that they were out of sight of the agitated mother bear. She pressed on until she located the hikers cowering behind the ridge and subsequently mauled them both before running off with her offspring. (One woman had bear spray and actually unloaded the whole canister on the bear, but it apparently had little effect on the sow’s desire to do harm to the perceived threat to her cubs.)

There is no doubt that a mother grizzly can morph into one of the most ferocious animals on the planet, if she feels that her cubs are in peril. But momma bears, at least in some areas, do not always look at humans as a threat. Consider the refuging behavior employed by sows with dependent cubs. This was first described in the population of Ursus arctos that frequent the McNeil River Sanctuary. At McNeil, there is a viewing pad, where all human observers are to remain when watching the bears. Biologists began to notice that mothers with cubs would approach near to the viewing pad when they wanted to nurse their young. During the nursing process, the mother bear lies on her back and her progeny climb onto her belly and suckle at one of her six nipples (they may move from one nipple to another until mom’s milk supply is temporary exhausted). During this time, mother and babies are more vulnerable to attack. If other bears are around, the sow will keep a close eye on the goings-on of her neighbors. If she feels threatened, she will quickly jump to her feet, sending the cubs tumbling to earth, and prepare to defend her offspring.

It turns out (as I mentioned in the last post) that in many areas where bear-viewing occurs, large males tend to be more wary of human groups. (It has been suggested that boar avoidance of people is a function of their being more likely to have had negative experiences with hunters, who usually target large males.) You can see this avoidance behavior at McNeil River, where many larger boars remain on the side of the river opposite the viewing pad. OK –so here is where it gets real interesting. Female bears have learned about these tendencies and as a result, in order to increase their security levels during these nursing bouts, some sows will sidle-up to our kind! Is that not awesome - that mother brown bears have learned to use bear-viewers to help take care of her cubs.

That female’s take advantage of ecotourists has been studied in British Colombia (Nevin and Gilbert 2005). These researchers found that female’s with dependent cubs catch more fish-per-unit-effort when ecotourists are present than when they are not. They concluded that this increase in foraging effectiveness was due to the fact fewer males are present when bear-viewers are around. (Other studies in this region have shown that large boars tend to fish more at night when humans vacate the fishing area, while more mothers with cubs fish during the day.)

We will examine an even more incredible phenomenon, cub caching, in my next post.

References:

Nevin, O. T. and B. K. Gilbert. 2005. Measuring the cost of risk avoidance in brown bears: Further evidence of positive impacts of ecotourism. Biol. Conserv. 123:453-460.

video

Paula, a very experienced and defensive sow, nurses her yearling cub, Racer. After nursing, Racer relaxes and enjoys the security of having a good mom. Video by Scott W. Michael.

* - I borrowed the saying “bjorn porn” from bear biologist Steve Stringham - we will discuss Steve and his amazing work in a future post!


Copyright (2008) Scott W. Michael

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