The taxonomic identity of the Pelecaniformes is currently in flux

Nature · Published 19 October 2026 Swipe more like this →

In short: For decades, we defined these waterbirds by a single physical trait: webbing between all four toes. However, modern molecular studies have revealed that this shared feature is actually a result of convergent evolution, forcing scientists to radically redraw the family tree of these aquatic masters.

Traditionally, the order Pelecaniformes was defined by 'totipalmate' feet—a specific type of webbing connecting all four toes. This group included a diverse array of birds, such as cormorants, frigatebirds, and tropicbirds. However, research from the early 21st century suggests these similarities are not due to common descent, but rather convergent evolution—adaptations that emerged independently as birds moved into similar aquatic environments.

As a result, the classification is in transition. The most widely accepted modern view separates many of these birds into new orders. The frigatebirds, gannets, and boobies are now often placed in the order Suliformes, while tropic birds belong to Phaethontiformes. The current definition of Pelecaniformes is more focused, encompassing pelicans, the shoebill, and the hamerkop, alongside families like herons (Ardeidae) and ibises (Threskiornithidae).

These birds exhibit remarkable physiological specializations. Many possess a bare throat patch of gular skin and nostrils that have evolved into dysfunctional slits, necessitating breathing through the mouth. They also feature a pectinate, or comb-like, nail on their longest toe to maintain their feathers. While their lifestyles vary—from the 'piracy' of frigatebirds to the deep-diving pursuit of cormorants—they remain a vital part of global ecosystems.

Human interaction with these species is complex. While many are of little direct significance, the guano from species like the guanay cormorant and Peruvian booby has been a massive fertilizer resource, with harvests in Peru reaching about 180,000 tons per year in the 1960s. However, they face modern threats, including the legacy of DDT, which caused thin eggshells and population declines in brown pelicans during the early 1970s, and the recent spread of highly pathogenic avian influenza.

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