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The BBC Guide To Bills

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Old Wednesday 2nd April 2003, 18:43   #1
peter hayes

 
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The BBC Guide To Bills

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 significant part 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.

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.

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.

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.

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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Old Wednesday 2nd April 2003, 22:27   #2
Andrew
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I have seen these Lapwings vibrate the ground and also Egrets shake their legs in water to flush out fish and shrimps then stab at them. I have also seen Seagulls do the Blackbird's routine of stomping on the ground to bring up worms.
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