Measuring population trends for water birds such as cormorants, gulls, and other water birds has been limited by available census data that go back only a few decades, making it difficult to know how and why bird populations fluctuated in the past. Until now.
A team of scientists led by uOttawa have discovered new ways to track how water bird populations have changed over time, and even when birds first colonized certain areas.
The method involves taking samples of lake sediment from small lakes and ponds on islands near the nesting bird colonies. Over time, sediments slowly accumulate at the bottom of lakes, recording a history of biological and chemical changes in lakes.
When birds colonize a new area, they begin to fertilize their nesting areas with guano and carcasses, drastically changing the chemistry of the water, and these changes are recorded in the sediments as they deposit at the bottom of lakes.
“We have found that several chemical markers in sediment track the abundance of bird populations in a given area,” explained lead author Dr. Kathryn Hargan, a postdoctoral fellow at the University of Ottawa.
The study showed that the abundance of chemicals such as sterols and nitrogen-15 in lake sediment was closely related to the density of birds nesting nearby.
“One of the biggest challenges we face in the ecological and environmental sciences is the lack of long-term monitoring data. Tools such as these offer a new perspective into tracking environmental changes going back hundreds even thousands of years”, said Prof. Jules Blais from the University of Ottawa, who led the research team.
“This technique allows us greater insights into historical wildlife populations,” said Professor Mark Mallory, a wildlife biologist and professor of Acadia University who was part of the research team. “We can then see how these wildlife populations responded to past environmental stressors, like changes to landscapes, hunting, or chemical contamination.”
The full research paper: Sterols and stanols as novel tracers of waterbird population dynamics in freshwater ponds is published in Proceedings of the Royal Society B.