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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