3,000 year old penguin guano helps estimate penguin numbers. Carrie Straight 05.03.01 Since no one has been keeping records of penguin populations in the Antarctic for the last 3,000 years, biologists needed to find a way to figure out how their numbers changed in the past. A team of Chinese scientists collected a core sample from the material at the bottom of a lake (a sediment sample). A large amount of the material at the bottom of this particular lake is created from penguin guano (the term used to describe excrement - urine and feces - in seabirds). The penguin guano has been adding up in the bottom of this lake for thousands of years. Because certain elements are found in plants and animals, especially carbon, the scientists can age the layers of the sediment in their core samples. They can also compare levels of other elements (like sulphur, phosphorus, and calcium) to tell how many penguins were around and how long ago it was. Using these techniques, they estimated the number of penguins in the area around the lake from 3,000 year ago until the present. It seems that there was a dip (decline) in penguins around 2000 years ago. What was happening then? Sun, Liguang, Zhouqing Xie, and Junlin Zhao. 2000. A 3,000-year record of penguin populations. Nature 407: 858. ©2001 The Aurora Collection, Inc. All Rights Reserved. Site Development by: Interactive Multimedia. Inc.