Seabirds have played an important role in human history and cultural experiences for thousands of years. From Greek mythology and the story of Daedalus and Icarus escaping imprisonment in Crete using wings made of seagull feathers^[1]The Story of Icarus. Jonathan Steffen https://www.jonathansteffen.com/writings/the-story-of-icarus/ (1969)., to the ancient Hawaiian legends that depict frigate birds as messengers for the gods^[2] Light, M. Hawaiian Superstition: Sea-Frigate Birds | USC Digital Folklore Archives. http://folklore.usc.edu/hawaiian-superstition-sea-frigate-birds/ (2017)., seabirds are embedded in human cultures. Understanding the taxonomy of seabirds is important to understand how their historical influences came about, and also to later understand why seabirds are so crucial to marine ecosystems.  

All About Seabirds

Seabirds have been classified and divided into four major orders: Sphenisciformes (penguins), Procellariiformes (albatross, petrels, shearwaters), Pelecaniformes (pelicans, cormorants, frigate birds), and Charadriiformes (gulls, terns, and alcids)^[3]What’s a seabird? Audubon California https://ca.audubon.org/what-s-seabird (2015)..

Sphenisciformes

Penguins are the sole family of the order Sphenisciformes. All 17 penguin species are flightless and restricted to the southern hemisphere. Penguins have unique physiological traits compared to flighted birds, such as poorly pneumatized bones, due to their flightless nature. Pneumatized bones are hollow, making them not only lighter, but also an integral part of the bird’s respiratory system.

Figure 1: King Penguins (Aptenodytes patagonicus)^[4]Gratwicke, B. King penguins racing back to feed their chicks. (2012).

Air sacs attach to the hollow spaces in the bones and allow for extra oxygen uptake, and circulation during flight. Instead of skeletal pneumatization the bones in penguin wings are flat, wide, and solid. This adaptation provides them with heavier, solid, and more structurally sound flippers for long-distance propulsion during high-speed swimming^[5]Ksepka, D. T., Werning, S., Sclafani, M. & Boles, Z. M. Bone histology in extant and fossil penguins (Aves: Sphenisciformes). J Anat 227, 611–630 (2015).. Penguins live in large colonies on the shore, and their abundance of fecal matter (guano) provides a significant source of nutrient input in arctic ecosystems.

Figure 2: Wing Bones of Flighted Bird vs Penguin^[6]Pinguins info – penguin – evolution about penguins. https://www.pinguins.info/Engels/Evo_vlieg_eng.html.

Procellariiformes

Also referred to as tubenoses, the 108 species in order Procellariiformes include albatrosses, petrels, and shearwaters. The name tubenose arises from the bird’s unique nasal structure. All birds have nares, or circular holes on their upper beak, which lead to nasal cavities and the respiratory system. Procellariiformes have special, tubular structures around their nares. These tubes serve many purposes, including channeling airborne scent to help the birds more accurately detect prey and to prevent saltwater from entering their nasal cavities^[7]Procellariiformes (Tubenosed Seabirds) | Encyclopedia.com. https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/procellariiformes-tubenosed-seabirds (2023).^[8]Freedberg, W. How Do Pelagic Birds Find Fresh Water At Sea? Distraction Displays https://blogs.massaudubon.org/distractiondisplays/how-do-pelagic-birds-find-fresh-water-at-sea/ (2018).. Members of the order Procellariiformes also have the most extensive variation in body size than any other order of birds. With wingspans ranging from 12 inches to 12 feet, Procellariiformes are soaring birds that spend most of their lives out at sea^[9]Procellariiformes. Avian Hybrids https://avianhybrids.wordpress.com/procellariiformes/ (2014).. Like Sphenisciformes, Procellariiformes breed in large nesting colonies where they feed on fish, amphibians, copepods, and even the carcasses of marine mammals. Their guano is also a major contributor to marine nutrients, and through hunting a wide variety of prey, they help structure marine food chains. 

Figure 3: Northern Giant Petrel (Macronectes halli)^[10]Smith, G. ‘Slobirdr’. Northern Giant Petrel (Macronectes halli). (2016).

Pelecaniformes

Pelecaniformes is our first order of sea birds with a global distribution. Comprised of 67 different species, this order is most notably identified with pelicans, anhingas, cormorants, and frigatebirds. One of the most significant characteristics of species in Pelecaniformes is the gular sacs below the mandible (lower jaw)^[11]Howard, L. Pelecaniformes (pelicans, tropicbirds, cormorants, and relatives). Animal Diversity Web https://animaldiversity.org/accounts/Pelecaniformes/.. The gular sac is a thick flap of skin that can expand to scoop prey out of the water, and can hold up to three gallons of water at a time. In addition to aiding in food capture, these birds can engage in gular flapping (similar to a dog panting) to cool themselves on hot days^[12]Diego, M. A. 1800 C. M. D. S. & Us, C. 92106 P. 619 523-4285 C. Excuse Me, What Do You Keep in Your Gular Pouch? – Cabrillo National Monument (U.S. National Park Service). … Continue reading. Pelecaniformes have many physiological adaptations for hunting, including the ability to dive into the water at extremely high speeds. To withstand the impact of the water, they have developed fused furcula and sternal keel^[13] Pelicans. https://birdsofseabrook.app.clemson.edu/taxa/t027-pelicans.html..

Figure 4: Australian Pelican (Pelecanus conspicillatus)^[14]Moses, H. Australian Pelican (Pelecanus conspicillatus). (2017).

The sternal keel is an extension of the sternum which provides an anchor site for their large flight muscles. The furcula (or wishbone) is a forked bone located above the keel which is used to strengthen the skeleton enabling it to withstand the rigors of flight^[15]Lowi-Merri, T. M., Benson, R. B. J., Claramunt, S. & Evans, D. C. The relationship between sternum variation and mode of locomotion in birds. BMC Biology 19, 165 (2021).. In most bird species, the keel and furcula are not fused because the skeleton doesn’t need the extra reinforcement; however, in diving birds such as Pelecaniformes, this fusion provides an even greater level of strength to the skeleton and enables them to withstand dives up to 40mph^[16]How Brown Pelicans Dive After Fish Without Breaking Their Necks. Audubon https://www.audubon.org/news/how-brown-pelicans-dive-after-fish-without-breaking-their-necks (2018).. Unfortunately, due to human exploitation, pollution, and overfishing, 22 of the 67 species in order Pelecaniformes are endangered. With that endangerment, we not only risk losing the species themselves, but also the important ecosystem services they provide through their food chain regulation and nutrient expenditure. 

Figure 5: Ventral view of pelican sternum ^[17]Fig.2 : Photograph showing ventral view of the sternum of Spot-billed… ResearchGate … Continue reading

Charadriiformes

The final order of seabirds are the Charadriiformes. This order contains 390 species of shore birds including gulls, plovers, sandpipers, auks, and terns^[18]Charadriiformes – shorebirds | Wildlife Journal Junior. https://nhpbs.org/wild/Charadriiformes.asp..

Figure 6: Masked Lapwing (Vanellus miles)^[19]Charadriiformes. Simple English Wikipedia, the free encyclopedia (2013).

Due to the extensive number of species within the order, there are multiple feeding adaptations that we should be familiar with^[20]Gulls, Terns, Plovers, and Other Shorebirds: Charadriiformes | Encyclopedia.com. … Continue reading. Species such as auks or puffins can swim, and catch their prey underwater. Skimmers such as terns fly low over the surface of the water and scoop fish up as they fly over. Species such as plovers or sandpipers, which hunt for invertebrates in the sand, rely on their sense of sight or touch to see or feel vibrations below. They’re able to use their long beaks to then retrieve their prey once they’ve identified its location in the sediment. Sandpipers and snipes specifically have developed a unique feeding adaptation called rynchokinesis, or the ability to flex their upper mandible independent of the lower mandible, to improve foraging capabilities. Rynchokinesis is an adaptation associated with cranial kinesis, or the ability to move both jaws (humans and other mammals are only able to move the lower jaw!). All birds are capable of cranial kinesis, but only specific shorebirds are capable of rynchokinesis^[21] Estrella, S. M. & Masero, J. A. The use of distal rhynchokinesis by birds feeding in water. J Exp Biol 210, 3757–3762 (2007).^[22]Gussekloo, S. W. S. & Bout, R. G. Cranial kinesis in palaeognathous birds. Journal of Experimental Biology 208, 3409–3419 (2005).. Charadriiformes are migrating birds, some of which travel over 10,000 miles each year! These large-scale migrations result in huge breeding colonies, where the birds will raise their young in simple, pebble-lined nests. Due to their migration patterns, and breeding settlements in nutrient-rich ecosystems, Charadriiformes have a significant impact on nutrient transfer and flow across oceans.

Figure 7: Rhynchokinesis in Common Snipe (Gallinago gallinago)^[23]Rhynchokinesis – photo documentation of gradual change in the upper mandible shape – Bird Ecology Study Group. … Continue reading

What Now?

Now that you’re familiar with the different orders of seabirds, the next time you take a walk on the beach, watch a documentary about the antarctic, or spot a migrating flock, take a minute to consider the individual species and how their unique physiological traits have prepared them for the life you’re observing!

Emily Padden

Research and Writing Intern

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