July 01, 2011 by William Keener
When William Keener got a report of a harbor porpoise inside San Francisco Bay in 2008, he knew this was big news: They had been absent since World War II. Now, Keener's group of researchers has turned the Golden Gate Bridge into a world-class wildlife observatory where anyone can see porpoises in action. Why have they returned? Did Bay cleanup efforts make the difference? While we can't know for sure, we can celebrate this rare case of a large mammal reintroducing itself into its former habitat.