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occurs just behind the wing tip. Some birds mix gliding with flapping to
achieve even greater energy efficiencies. Coordinating their gaits increases
that efficiency even further. So, when a lead bird in a group of birds decides to
glide, the rest will follow. When the lead bird decides to begin flapping again,
the rest do likewise. Synchronization in both position and timing make for the
most efficient and economical way of group flying and is particularly useful
for birds migrating over long distances.
Walking, Hopping, and Running
Flying is obviously of great importance to most birds, but a lot of birds depend
on being able to get along on the ground to forage for food, to find a mate, or
to build a nest. They may choose to walk, run, or hop. Some birds get along on
the ground by doing only one of these; others engage in more than one such
behavior. Size once again plays a part in determining which one is best suited to
the bird. The ostrich may be capable of jumping—that is, leaping of the ground
with both feet at once or slightly out of synch—though it doesn't do this as a
regular mode of locomotion and this movement could hardly be described as
hopping. Most small birds hop as a way of getting around on the ground. They
are light, so the effort involved in hopping is comparatively low. For larger birds
hopping becomes a very inefficient way of getting around; they are heavier and
the energy required to hop is much greater. In small birds hopping is usually
a symmetrical action, with both feet leaving and returning to the ground at
the same time. Some larger birds such as small crows may demonstrate an
asymmetrical hopping action during which one foot leaves the ground and
subsequently returns to the ground slightly in advance of the other.
Pied wagtails, although not a great deal bigger than those birds that favor
hopping such as the house sparrow, opt to run rather than hop. It is perhaps
true to say that rather than run they walk at very high speeds. A run is
distinguished from a walk by the inclusion of a suspension phase during which
FIG 4.63
Bird hopping sequence.
