Phaethontiformes

 

Classification In the phylogenomic study by Jarvis et al (2014), which achieves high resolution by performing DNA sequencing on whole genomes, Phaetontiformes are now placed in close proximity with Pelicaniformes and Core Waterbirds.

Tropicbirds frequently catch their prey by hovering and then plunge-diving, typically only into the surface-layer of the waters. They eat mostly fish, especially flying fish, and occasionally squid. Tropicbirds tend to avoid multi-species feeding flocks, unlike the frigatebirds, which have similar diets.

Tropicbirds are usually solitary or in pairs away from breeding colonies. There they engage in spectacular courtship displays. For several minutes, groups of 2–20 birds simultaneously and repeatedly fly around one another in large, vertical circles. Tropicbirds generally nest in holes or crevices on the bare ground. The female lays one white egg and incubates for 40–46 days. The young are not able to fly initially; they will float on the ocean for several days to lose weight before flight.

Tropicbird chicks have slower growth than nearshore birds, and they tend to accumulate fat deposits while young. That, along with one-egg clutches, appears to be an adaptation to a pelagic lifestyle where food is often gathered in big amounts, but may be hard to find.

Jarvis ED et al (2014): Whole Genome Analyses of Birds

http://en.wikipedia.org/wiki/Tropicbird