Climate change is altering and destroying important habitats that America’s migratory birds depend on, the National Wildlife Federation said Tuesday in a report.

In years past, tens of thousands of red knots crowded the sandy beaches of Mispillion Harbor in Delaware Bay, gorging on fresh horseshoe crab eggs spawned in such abundance they turned the shoreline a gelatinous green. Smaller than a gull but larger than a robin, the shorebirds have one of the longest-distance migrations known in the animal kingdom. Each year, the ruddy-breasted birds fly to the Canadian Arctic from their winter home in Tierra del Fuego at the tip of South America. And each year, there are fewer and fewer.