Gleaning (birds) - Other Foraging Techniques

Other Foraging Techniques

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.

A feeding technique that is somewhere between gleaning and hawking is where a bird flies from a perch and takes prey off foliage; this is called "sally-gleaning". The pygmy tyrants of South America are tiny flycatchers that feed this way. The todies of the Caribbean employ a distinct version of sally-gleaning. These small birds choose a perch within their lush forest and plantation habitats in the Greater Antilles, from which they scan the undersides of leaves above them. Upon spotting an insect or spider, they fly up in an arcing sally, pluck their prey item without stopping, and complete the arcing movement to land on a new perch.

An unusual feeding strategy is that of the oxpeckers of Africa. They perch on living animals and glean parasites from the animals' hides. On furry animals, such as buffalo, giraffe, and donkey, these birds run their bills through the fur of the animal, using a scissors-like motion to extract ticks and lice from near the skin. When they pull the insect out to the end of the fur, they catch it and eat it. (On animals with bare hides, such as rhinoceros and hippopotamus, oxpeckers pick at any open wounds the animals happen to have, consuming blood and puss, and possibly keeping the wounds free of maggots.) Historically, rhinoceros and other large wild mammals have been among the favored hosts, but as the populations of large mammals in the African savanna have changed in modern times, the population and range of both Red-billed and Yellow-billed Oxpecker have also changed, and now the birds will use donkeys and domestic cattle as hosts.

There are other tactics. Dippers forage underwater in fast-moving streams. Common Grackles have been observed to follow farmers’ plows to glean the grubs exposed in the fresh soil. Similarly, on the island of Borneo, the Bornean Ground-cuckoo will follow wild pigs and sun bears as they turn up soil while foraging in the forest. Brewer's blackbirds are often seen in parking lots, where they pick off dead insects from car grilles. Some hummingbirds are known to take prey items from spiderwebs.