Another article from the yahoo ethology group:
http://www.pigeon.psy.tufts.edu/psych26/birds.htm
Hungry Egyptian vultures use ingenuity in obtaining their food.
Since the shells of ostrich eggs are too hard to break open by simply
pecking at them, the vultures use rocks to assist them. According to
reports by Jane Goodall from Tanzania, the vultures will search as
far as 50 yards from the coveted egg in order to find a proper
smashing tool. Interestingly, the forward jerking movement of the
vultures' head exhibited when breaking an egg with a stone is very
similar to the movement used when the bird simply pecks to break open
an egg. Other species of birds break eggs open by throwing them down
on stones. However, this behavior is not considered tool use because
the stone is not being used as an extension of the bird's body.
Alcock(1975) theorized that the vultures originally threw eggs to
break them open. They then evolved from throwing the eggs to
throwing rocks at the eggs. The use of rocks to break the eggs open
probably began when a vulture accidentally hit an egg with a rock.
Vultures' aim in stone-throwing is poor, hitting the target with only
40-60% of their throws. Despite their imperfect aim, the vultures
persist until they succeed in cracking the egg. A study by C.R.
Thouless in 1989 supports Alcock's theory with its finding that the
vultures prefer to use egg-shaped stones. The use of stone-shaped
eggs belies a connection to the usual behavior of throwing an egg
against the ground to crack it.
An interesting study demonstrated that shape not only dictates the
tools used by vultures, but also the objects which they choose to
crack(National Geographic Society, 1972). The study showed that
although vultures will try to use a stone to break open a green or
red egg-shaped decoy, they do not attempt to open white cubes.
Observations by C.R. Thouless and his co-workers(1989) of young
vultures reared without exposure to adults proved that throwing
stones at eggs is an innate, not learned, skill. However, the
vultures do need to learn that ostrich eggs are a rewarding source of
food before they begin cracking them with rocks. Such learning
occurs when a young vulture encounters an egg which has already been
cracked by another bird and tastes its contents.
The woodpecker finch, residing on the Galapagos islands, is the most
amazing of Darwin's finches. Its talents include tool use as well as
tool fabrication. In the above photograph, the finch is prying grubs
out of a tree branch with a cactus spine. A woodpecker's long barbed
tongue enables it to extract grubs from branches without the
assistance of a tool. On the other hand, the woodpecker finch
compensates for its short tongue by grasping a cactus spine in its
beak and prying grubs out of the branch with the cactus spine. The
finch then drops the cactus spine and holds it under its foot while
eating the grub. The cactus spine is carried from branch to branch
for reuse.
Observations by Millikan and Bowman(1967) reveal that the finches
adjust their posture and manipulation of the tool according to its
size and shape. They also discovered that the woodpecker finches
were more likely to seek out and use tools with an increase in hunger
level. Milikan and Bowman also conducted a study in which a
different species of finch from the Galapagos islands, the large-
cactus ground finch, was caged next to a group of woodpecker finches.
Although the large-cactus ground finches do not use tools to probe
for grubs in their natural environment, they acquired similar tool
usage to the woodpecker finch when caged in such close proximity.
Other species of finches, however, did not learn to use tools as
probes when they were caged next to the woodpecker finch.
A researcher was fortunate enough to observe a young woodpecker
finch's acquisition of the skill of using the cactus spine. The
finch began by attempting to obtain grubs from a tree branch simply
by using its beak. When that system frequently failed, the finch
implemented a twig in order to reach further into the branch.
Another finch was observed snapping off a part of a forked twig in
order to fashion a superior tool. Millikan and Bowman(1967) also
observed woodpecker finches shortening long cactus spines in order to
form more manageable tools. This manipulation of an object for tool
use is particularly impressive.
Brown(1975) posits that woodpecker finches would be replaced by
woodpeckers or nuthatches if either of those species were to come to
the Galapagos islands. His basis for this theory is that woodpeckers
and nuthatches have more effective morphological means for
accomplishing what the woodpecker finch does with tools.
The green heron drops a small object onto the surface of the water.
Fish swim to the surface, hoping that the object might be prey. The
heron then snatches the unsuspecting fish which come along to inspect
its bait.
The practice of bait-fishing is rare among green herons. The fact
that few herons use bait-fishing indicates that it is not an innate
behavior. Moreover, the infrequency of bait-fishing suggests that
the behavior is not culturally transmitted. The roots of using
objects to attract fish are unclear. One theory suggests that herons
are imitating human behavior when they use bait for fishing.
However, the fact that attempts to teach herons to use bait for
fishing have failed suggest otherwise.
Another possibility is that herons learn to use bait for fishing
through experience, i.e. the heron accidentally drops an object in
the water and sees the object's attraction to fish. Some researchers
believe that making the connection between dropping something on the
water and seeing the crowd of fish that results and intentionally
dropping bait into the water is very difficult. According to these
researchers, only the exceptionally intelligent herons acquire the
skill of bait fishing. The intelligence requirement accounts for the
small percentage of green herons who engage in bait-fishing. Other
researchers argue that the reason for the infrequency of the behavior
is that few herons actually have the opportunity to observe the
results of dropping an object into the water.