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How do tropic bird chicks differ from most other pelecaniform chicks at hatching?

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Three eastern white pelicans with black-tipped wings take off from a muddy shoreline, wings outstretched, with blurred green vegetation in the background. — Pelecaniform European white pelicans (*Pelecanus onocrotalus*) in flight.

Unlike most other pelecaniform chicks, which are hatched in a helpless and essentially naked condition, tropic bird chicks are exceptional because they possess thick down at hatching. Additionally, due to this early development, tropic bird chicks are sometimes left unattended by their parents as early as the day they hatch.1