Seabirds converge on ocean life yet nest in vast colonies
Seabirds are birds adapted to marine life, often showing convergent evolution as similar ocean niches reshape unrelated lineages. They typically live longer, breed later, and raise fewer young than many land birds, investing heavily in each chick within colonies from dozens to millions.
Their story runs deep in time. The first seabirds appeared in the Cretaceous, and because the sea buries remains quickly they are well represented as fossils. The earliest, the Hesperornithes, were flightless foot-propelled divers with sharp teeth in their beaks and apparently left no descendants, but Tytthostonyx glauconiticus, also Cretaceous, already hints at petrels and frigatebirds. Modern seabird families arose in the Paleogene.
Which birds count is partly convention. Scientists Elizabeth Shreiber and Joanna Burger observed that the one trait all seabirds share is feeding in saltwater, then conceded that some do not. Penguins are always included, while loons and grebes, which breed on lakes and winter at sea, are usually classed as water birds, and sea ducks, herons and waders are generally left out too. Gerald Mayr's 2010 clade Aequornithes gathers petrels, penguins, gannet relatives and pelicans alongside storks and loons.
Body design tracks lifestyle. Long wings with low loading suit wanderers of the open ocean, while divers have short, heavily loaded wings. Salt glands in the head flush out an almost pure sodium chloride solution, and dense waterproof plumage over thick down keeps most species dry and warm, cormorants and some terns excepted. Colours are mostly black, white or grey, probably for camouflage. Many feed at the surface where currents bunch up krill, squid and small fish; prions sieve plankton through comb-like lamellae, and albatrosses snatch fast prey with hooked bills.
People have long relied on them as food and as guides to fish and land. Oil spills, fishing, offshore development, climate change and severe weather now threaten many species, and wildlife refuges and changed fishing methods are among the responses.
Source: Seabird
