Foraging for invertebrate prey on the ground often involves gleaning the leaf litter of the forest floor, sometimes flicking, flipping, or scratching through dead leaves. Birds can use their bills to flick or toss dead leaves from the ground to reveal prey residing beneath. The leaftossers of Central and South America and the pittas and laughingthrushes of Asia do this. An example of a bird that employs flipping is the ovenbird, a species of North American wood-warbler. It deliberately turns over leaves on the ground to search for spiders, worms, and such underneath. In other parts of the world, similar leaf-flipping behavior has been observed in unrelated birds, such as the jungle babbler of India. Some birds, such as hummingbirds, will use their wings to create a blast of air to roll leaves over. Other birds rake a foot through the leaf litter, like a chicken, for the same purpose. This has been observed in buttonquails. Some American sparrows, such as the green-tailed towhee, perform a double-scratch by raking both legs simultaneously through the leaf-litter. They then catch prey items dislodged by the disturbance. Ground-foraging birds can be very hard for humans to observe, as they often occupy densely vegetated habitat, as in the case of the Bornean wren-babbler, which specializes in gleaning leaf litter in gullies in the forest of Southeast Asia.