Two hundred years ago, there were three bird species native to North America that were known for nesting in huge colonies: the Passenger Pigeon, Carolina Parakeet and the Tricolored Blackbird. In some areas, millions of these birds blanketed the sky. Now, all but the Tricolored Blackbird is extinct -- and it's hanging on by a thread. Please help us save this remarkable California bird. (photo by Kelley Weintraub)