Enthusiastic birders flock to Mount Desert Island annually to celebrate the diversity of Acadia birds. Now, as the Acadia Birding Festival marks its 20th anniversary May 31-June 3, the gathering comes during a time of urgency: A new study identifies as many as 66 species of Acadia birds that could become locally extinct by the year 2050, if nothing is done to reduce carbon emissions. This is the Year of the Bird, to celebrate the 100th anniversary of the Migratory Bird Treaty Act that protects birds, and also sound the alarm about climate change’s potential impact and other threats, with the hope of preventing species from becoming modern-day equivalents of the canary in a coal mine.