Houseguests can be a nuisance but you can get used to them and so too can Magellanic penguins, according to new research by the University of Washington in Seattle. The researchers were studying whether human visitors who walked through penguin nesting sites at the world's largest Magellanic colony in Punta Tombo, Argentina, caused long-term stress damage to the colony. They watched for signs of stress, measured by characteristic "head turning" and by blood hormone levels. Penguins paid little attention to human visitors once used to them and seemed indifferent after about 10 days' exposure to talking, singing and picture-taking humans.