Thousands of snow geese touch down at a Pennsylvania reservoir each spring, turning sunrise into a loud, swirling liftoff that draws big crowds. A few dozen birdwatchers gather before dawn at the Middle Creek wildlife preserve to catch the moment. After sunrise the flock rises from the water’s surface suddenly, circles and then heads out to nearby fields to feed. The state Game Commission says Middle Creek has hosted huge groups of 100,000 or more in recent years. Scientists warn the geese have grown so abundant that their numbers have damaged breeding grounds in the Canadian Arctic. There are also concerns about avian influenza.