From National Geographic:
Ostriches don't bury their heads in
the sand—they wouldn't be able to
But they do dig holes in the
dirt to use as nests for their eggs.
Several times a day, a bird puts her
head in the hole and turns the eggs.
So it really does look like the birds
are burying their heads in the sand!
From the San Diego Zoo:
.. that’s a myth: ostriches do not
bury their heads in the sand!
ostrich senses danger and cannot run
away, it flops to the ground and
remains still, with its head and neck
flat on the ground in front of it.
Because the head and neck are lightly
colored, they blend in with the color
of the soil. From a distance, it just
looks like the ostrich has buried its
head in the sand, because only the
body is visible.
From ABC Science:
The ostrich does many things, but
hiding its head in the sand is not one
Ostriches have three main strategies
- they can run away,
- or they can try to hide (eg,
when nursing the eggs).
they will sometimes lay flat on the
ground, with the long neck and head
also on the ground. In the rippling
heat haze of their native Africa, they
can look just like a grassy mound.
From Straight Dope:
There are two theories about how this
rumor got started.
According to the World Wide Fund for
Nature, the ostrich lowers its head
toward the ground in reaction to
danger, especially when it's sitting
on a nest (the female keeps the eggs
warm during the day and the male sits
on the eggs at night).
Male ostriches use their bills to dig
shallow nests in the sand and move
their eggs around. From a distance,
this could look like the ostrich's
head is disappearing in the sand.
That's the other theory.