Geoscience Reference
In-Depth Information
it with its beak, took off, and then let go. In many instances, the bird left tracks dir-
ectly in front of the clam or whelk's burrow, followed by a take-off pattern. When
I look a little farther away, a bounce mark and broken shell show exactly where it
impacted, and trampling around the shell pieces tells of how the gull successfully
dined on its gravitationally prepared meal.
Birds may also take advantage of seashores with good rock outcrops or paved
beachside parking lots, using these for opening their naturally packaged seafood.
I've watched American crows do this in the Florida Everglades, in which they drop
freshwater snails onto paved roads to break them open. In urban environments of
Japan, carrion crows (
Corvus corone
) learned a variation of this technique, used
with walnuts, in which they place these on the crosswalks of busy streets for cars to
run over and break. They then wait for pauses in traffic provided by stoplights, fly
down to quickly eat their meals, then take off just before the light turns green.
Beakmarksmadebybirdslivingawayfromshorelines,especiallyinforestsor
plains, are a little different, but mostly because these are preserved in different sub-
strates. Insect-eating birds, such as grackles or starlings, systematically insert their
beaks into soil or ground vegetation to find their food. Northern flickers in partic-
ular are both persistent and insidious in their ground probing. These birds find an
ant nest, insert their beaks into the main burrow shaft, and open wide (gape). This
causes enough of a disturbance to encourage ants to run directly toward its mouth,
which is where its long tongue picks them off, rapid-fire; for dessert, it may then
drill further down to get some delectable ant larvae. Either way, this probing and
gaping results in a conical hole at the top of the ant nest, and its depth corresponds
roughly with the length of the bird's bill. Seeing that ant eating has been proposed
as a lifestyle for some theropods, such as the Late Cretaceous
Xixianykus zhangi
of
China, trace fossils resembling those formed by gaping might also have been pre-
served in fossil ant nests.
Meanwhile, above the ground and in the trees, woodpeckers and related birds
either drill into trees or peel off bark to expose bountiful supplies of wood-boring
