A new study on stress could help us protect the world’s endangered species.
Professor Rudy Boonstra of the Department of Zoology at UTSC and his colleagues looked at 100 song sparrow territories in British Columbia, home to numerous song sparrow predators such as crows, snakes, raccoons, and cats. Boonstra and his team added feeders to some areas, artificially increasing the birds’ food availability.
They found that the sparrows’ stress levels varied according to both their food intake and the number of predators threatening them. This stress in turn affected how many young they had-meaning that stress is probably an extremely important factor in the long-term survival of endangered species.
Post-doctoral researcher Mike Clinchy, of the University of Western Ontario, co-authored the study with Boonstra. They found that in the toughest areas, where the birds were threatened by many predators but were not given any feeders, the birds produced on average two fledglings. When feeders were placed in the area, the birds produced three fledglings-the same number that they produced in areas with no feeders but with few predators.
“You would therefore expect sparrows who have a feeder and live in a low predator area to have four kids,” said Clinchy. “But instead they get six kids, a 200 per cent increase.” This is dramatic, he says.
Boonstra found a similar effect in snowshoe hares in the Yukon ten years ago. The hares in a low-predator environment with supplemented bunny chow produced 11 times more young than ones without added chow. The question then was “what the possible mechanism could be,” says Clinchy.
The answer is stress. The sparrows and the hares felt various amounts of stress depending on which environment they lived in, and stress affects reproduction. Rudy thought that perhaps because these animals constantly have to worry both about finding food and avoiding bigger animals, this detracts from their ability to produce offspring.
Humans often experience this feeling of “kill or be killed” during war. “When you are taken out of a ‘kill or be killed’ situation [after a war],” explains Clinchy, “you still suffer from post-traumatic stress disorder for years afterwards, and often develop ulcers and adverse health effects. But for animals the stress is chronic-they are always under this threat.”
Stress levels in the song sparrows were estimated by measuring levels of the stress hormone corticosterone. Clinchy explains how this hormone works: “You’re walking down the street and you see a lion. Adrenaline kicks in and gets you running. But adrenaline is not what keeps you running; what keeps you running is corticosterone. It kicks in about about three minutes.”
The hormone shuts down everything in the body that is not needed for immediate survival, such as sexual reproduction and the ability to fight disease. All the body’s energy is devoted to short-term survival. “But long-term exposure to these stress molecules results in all sorts of adverse health effects,” explains Clinchy.
Clinchy and Boonstra found the highest corticosterone levels in the birds that had the fewest young, and the lowest corticosterone levels in the birds that had the most young. “So that tells us,” reveals Clinchy, “that both food and predators are going together to determine what the birds’ stress hormone levels are.”
“Because animals are always making this trade-off between finding food and avoiding predators,” adds Boonstra, “by manipulating both, let’s say by reducing predators and increasing food, you could maximize their chances for survival and reproduction. But in the history of conservation people have been doing only one or the other, with modest success.”
Canada’s 2002 Species at Risk Act encourages conservation efforts to be more cost effective. With the results of this study, conservation dollars could be used more efficiently. Clinchy explains, “If I take a threatened species and I add food and also reduce predators in their environment, I’m going to get more bang for my buck.”
But not every conservation biologist would agree with this-many of the most threatened species are large predators, like bears, wolves, and panthers. Boonstra counters, “We do not want animals to go extinct under any circumstances. In the current mindset, taking animals’ lives is unacceptable, but having species go extinct is much, much more unacceptable.”
