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A probe into the world of shorebird cutlery. |
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 When applied to people, the expression "living from hand to mouth" implies hard times and a tough existence. Birds, of course, don't possess hands and, with few exceptions, all manipulation of food has to be done with just one part of the body - the bill. Bills come in all shapes and sizes and, especially true of shorebirds, they are used with great dexterity. Bill length and shape are two obvious adaptations enabling different species to specialise in choice of prey and catching method.
Broadly speaking, a long-billed shorebird avoids competition with a short-billed species by probing at a different depth, even though both may be taking precisely the same food, for example, insect larvae. This bald statement glosses over complex techniques used in the pursuit of prey. Shorebirds feed actively and locating food requires an artful combination of several senses, not just touch.
It may come as a surprise to learn that some long-billed species may never actually see what they eat. Snipe use a long bill to probe in damp ground. Worms form a significantpart of their diet. Prey is located by feel and sucked directly inside the bird's mouth and swallowed. All long-billed shorebirds have highly sensitive bill tips that give the appearance of being rigid and fixed in shape. Actually, they are pliable and can flex and wiggle. Curlews have the longest bill and use it in two ways. On the one hand, it can delve deep into mud for soft molluscs and lugworms; on the other hand, despite a fragile appearance, its tip can be used as a hammer to break open crabs.
A long bill is often linked to long legs enabling some species to wade and probe at the same time. A scan across estuarine habitat reveals the full extent of permutations. Curlews feed belly-deep in water or pick morsels of food from the surface at lesser depth. Bar-tailed godwits use a slender, delicately upcurved bill to drive deep into the mud's surface with a side-to-side motion, probing for invertebrates. Redshanks, knots and dunlins all concentrate close to the surface and pick off tiny snails and minutiae.
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Other species are much more energetic in their endeavours. Greenshanks are similar to redshanks in size and general proportions, but this does not indicate a similar feeding strategy. Greenshanks hunt small fish, shrimps and other animals in pools and shallow channels. They wade in an alert posture and make swift jabs at prey. They disturb quarry by 'dancing' and make quick runs to startle it.
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On rocky shores, turnstones use a short anvil-shaped bill to forage among pebbles and wrack for small prey. Turning over stones is just one hunting method. They also synchronise bill, eye and body movements to roll up fine green seaweed to expose and then snatch sand-hoppers.
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Plovers are a large family of shorebirds that rely heavily on eyesight, rather than a specialised bill shape, to find food. Lapwings epitomise this behaviour. They feed on pasture and ploughed fields, using the typical plover tactic of repeatedly running a short distance, then pausing and pouncing on a victim on the ground, maybe a leatherjacket or earthworm. The bill is purely functional,although it is well suited to pulling food items from among roots and tussocks. Lapwings do something unusual to attract prey - they patter one foot on the ground. This action is accompanied by a sideways cock of the head. Are the birds listening or looking? Nobody knows for sure. However, one thing is certain, the preliminary foot-pattering must help in disturbing ground prey.
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 Among shorebirds, oystercatchers are probably unique in using bill skills that have to be taught by parents to young. Oystercatchers feed on mussels and employ two methods to extract them. Some smash the shell with a hammer blow; other, more dextrous individuals, open the shell with their sharp mandibles by cutting through the muscle holding the two halves together.This is more difficult to do but, once the skill has been mastered, it demands less effort than hammering. However, there is a rub. Young birds take several months to learn the actions from their parents but, having been taught one feeding method, they cannot easily switch to the other. The reason is not connected with an inability to learn the opposing technique, it is more fundamental than that. A bird trained to be a shell-smasher cannot easily become a shell-opener, simply because using the bill as a hammer blunts it!
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