Seeds are scattered widely by wind, water, and animals. Tumbleweeds break off near the ground in the autumn when their seeds are ripe. Their seeds are then scattered when the wind tumbles the plant along the ground. Some seeds are buoyant and are carried by water currents from place to place. Some weeds are covered with hooks, spines, or barbs that enable them to adhere to clothing and animal fur and feathers. Birds and other animals eat many kinds of fleshy fruits; in many cases the seeds pass through their digestive tracts unchanged and are deposited far from where the fruit was consumed. Squirrels often bury nuts some distance away from the tree that bore them. Many of the nuts are never found by the squirrels, and the seeds they contain may eventually develop into new plants.