Red knot birds are becoming smaller as temperatures warm in their Arctic breeding grounds. But the migrating birds don't pay the price for this climate-caused shrinkage until they arrive at the more stable climate of their tropical winter homes. According to a new study by Jan van Gils and colleagues, the smaller red knots have shorter beaks that prevent them from reaching quality mollusk meals deep in the tropical sand, forcing them to subsist instead on lower quality mollusks and seagrass. As a result, survival rates are down among red knots born in warm Arctic years, the researchers note. The red knots are one of several animals to shrink in size in response to climate warming. Newborn red knots depend on a "bloom" of insects that appears after the Arctic tundra melts as their main supply of food, but climate change has pushed this bloom earlier and out of sync with red knot hatching. Van Gils and colleagues' 33-year study of migrating red knots confirms that birds born in warm and lean Arctic years arrive in West African wintering grounds with shorter beaks that can only dig up one-third of their available preferred prey. Snowmelt in the red knot breeding grounds is occurring earlier and earlier, changing at the rate of about half a day per year, the researchers say, and this warming could be affecting the survival of other migrating animals beyond the red knots. In a related Perspective, Martin Wikelski and Grigori Tertitski discuss the implications of this new "global ecological warning sign."