Characteristics of Pelecaniformes
The order pelecaniformes contains six families,
five of which are found in the Galapagos. The features that unite
these families are the presence of a webbed foot that includes
all four toes and the presence of a throat sac (gular sac). This
sac is most highly developed in pelicans and frigate birds, but
is also very obvious in boobies and cormorants. In pelicans, the
pouch is used as a fish trap while in frigate birds it is used
as a mating display. When observing boobies and cormorants, it
is not unusual to see their sacs somewhat extended and fluttering
back and forth (gular fluttering). Gular fluttering in birds is
the equivalent of panting in mammals and these poor birds, often
sitting on a nest in the hot sun, are trying to shed excess heat.
An additional characteristic of pelecaniformes
cannot be seen in living birds, but is very obvious in the many
skeletal remains littering the colonies. All birds have a structure
called the furcula (the wishbone of our Thanksgiving turkey).
The furcula is a springy, v-shaped bone, that helps raise the
wing during the up-stroke. On the down-stroke the fucula is stretched
and then, when the wing relaxes, the furcula snaps back and helps
push the wing up. The arms of the furcula are attached to the
shoulder and the fused tip of the v is suspended above the breast
bone. pelecaniformes, however, are primarily gliders and do not
flap frequently. In these birds, the v tip of the furcula is solidly
fused to the breast bone and the arms are much more sturdily built
to help support the wings.
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