It wasn't until chicks with limited human exposure reached 40 to 50 days old that they showed a stress response like the newly hatched chicks in areas frequented by humans, said researcher Brian Walker, who led the work as part of his doctoral thesis at the UW. He is now an assistant professor of biology at Gonzaga University in Spokane.
Magellanic penguin chicks are hatched in a very immature and helpless condition. Walker's group found that by the time they reached 70 days old, nearly the time of fledging, chicks in human-visited areas had become far more accustomed to the presence of people than those in non-visited areas.
"In the tourist areas, you can walk among them and they put up with you. But when you walk over the hill to the places where tourists don't go, they're much more skittish. They run away or dive into their nests," he said.
The research was conducted at a penguin reserve at Punta Tombo, Argentina, with three separate sampling periods in November and December 2001 and January 2002. Chicks aged 6 to 7 days were captured and blood was drawn to measure the level of a hormone called corticosterone. The first sample was obtained within three minutes of capture to establish a baseline because, unlike a hormone such as adrenaline, it takes several minutes for corticosterone to build up in the bloodstream after a stressful event, such as being captured. Additional blood samples were drawn after 30 and 60 minutes. The same procedures were followed when the chicks were 40 to 50 days old and again two weeks before fledging, which occurs when the chick is about 75 days old.
None of the chicks demonstrated an elevated baseline corticosterone level. But 30 minutes and 60 minutes after capture, newly hatched chicks regularly visited by humans had levels more than three times higher than undisturbed chicks. At 40 to 50 days old, the levels were nearly the same for chicks at 30 and 60 minutes after capture, and for those near fledging the levels were almost identical between visited and undisturbed chicks.
But even when the hormone levels evened out between the two groups as the chicks got older, their behavior was different. Nearly fledged chicks in tourist areas did not flee until people were within two feet, while those in the areas not visited by tourists sought safety when people were still 30 feet away.
The research will be published in the October issue of Conservation Biology, a journal of the Society of Conservation Biology. Co-authors are Dee Boersma and John Wingfield, UW biology professors and Walker's doctoral advisers. The work was funded by the Wildlife Conservation Society, the American Ornithologists' Union and the American Museum of Natural History.
There is no evidence of short-term negative effects, such as different growth rates or weight differences at fledging, caused by distinct differences in corticosterone levels between newly hatched chicks in tourist and non-tourist areas of the reserve, Walker said. But it is unclear what later effects the elevated stress hormones might have.
"We don't know yet what it means ?it might mean nothing, but it will take more research to be sure," he said. "We are seeing evidence in other species, including humans, that some detrimental physiological changes that happen to adults can only be traced back to stressful situations or elevated corticosterone levels when they were young."