Editing Seabird (section)

=== Diet and feeding ===
Seabirds evolved to exploit different food resources in the world's seas and oceans, and to a great extent, their [[physiology]] and [[ethology|behaviour]] have been shaped by their [[diet (nutrition)|diet]]. These evolutionary forces have often caused species in different families and even orders to evolve similar strategies and adaptations to the same problems, leading to remarkable [[convergent evolution]], such as that between auks and penguins. There are four basic feeding strategies, or ecological guilds, for feeding at sea: surface feeding, pursuit diving, plunge diving, and predation of [[higher vertebrates]]; within these guilds, there are multiple variations on the theme.<ref name="Castro">{{cite book |last1=Castro|first1=Peter|last2=Huber|first2=Michael E.|date=2003|title=Marine Biology|location=University of Michigan|publisher=McGraw-Hill|page=186|isbn=0070294216}}</ref>

==== Surface feeding ====
Many seabirds feed on the ocean's surface, as the action of marine [[ocean current|currents]] often concentrates food such as [[krill]], [[forage fish]], [[squid]], or other prey items within reach of a dipped head.

[[File:Wilson's storm petrel.jpg|thumb|left|[[Wilson's storm petrel]]s pattering on the water's surface]]

Surface feeding itself can be broken up into two different approaches, surface feeding while [[bird flight|flying]] (for example as practiced by [[gadfly petrel]]s, [[frigatebird]]s, and [[storm petrel]]s), and surface feeding while swimming (examples of which are practiced by [[gull]]s, [[fulmar]]s, many of the [[shearwater]]s and gadfly petrels). Surface feeders in flight include some of the most acrobatic of seabirds, which either snatch morsels from the water (as do frigatebirds and some terns), or "walk", pattering and hovering on the water's surface, as some of the storm petrels do.<ref>{{cite journal|author=Withers, P. C. |year=1979|title=Aerodynamics and hydrodynamics of the 'hovering' flight of Wilson's storm petrel |journal=Journal of Experimental Biology |volume=80|pages= 83–91 |doi=10.1242/jeb.80.1.83|url=http://jeb.biologists.org/cgi/reprint/80/1/83|doi-access=free|url-access=subscription}}</ref> Many of these do not ever land in the water, and some, such as the frigatebirds, have difficulty getting airborne again should they do so.<ref>Metz, V. G. and Schreiber, E. A. (2002). Great Frigatebird (''Fregata minor''). In ''The Birds of North America'', No. '''681''' (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA</ref> Another seabird family that does not land while feeding is the [[Skimmer (bird)|skimmer]], which has a unique fishing method: flying along the surface with the lower mandible in the water—this shuts automatically when the bill touches something in the water. The skimmer's bill reflects its unusual lifestyle, with the lower mandible uniquely being longer than the upper one.<ref name = "HBW">{{Citation | first = R. L. | last = Zusi |editor-first = Josep | editor-last = del Hoyo | editor2-first = Andrew | editor2-last = Elliott | editor3-last = Sargatal | editor3-first = Jordi | contribution = Family Rynchopidae (Skimmers) | title = [[Handbook of the Birds of the World]]. Volume 3, Hoatzin to Auks | year = 1996 | pages = 668–675 | place = Barcelona | publisher = Lynx Edicions | isbn = 84-87334-20-2 }}</ref>

Surface feeders that swim often have unique bills as well, adapted for their specific prey. [[Prion (bird)|Prions]] have special bills with filters called [[lamella (zoology)|lamellae]] to filter out [[plankton]] from mouthfuls of water,<ref name="Brooke">Brooke, M. (2004). ''Albatrosses and Petrels Across the World''. Oxford University Press, Oxford, UK {{ISBN|0-19-850125-0}}</ref> and many albatrosses and petrels have hooked bills to snatch fast-moving prey. On the other hand, most gulls are versatile and opportunistic feeders who will eat a wide variety of prey, both at sea and on land.<ref name="Davenport">{{cite book |last1=Davenport|first1=John|last2=D. Black|first2=Kenn|last3=Burnell|first3=Gavin|last4=Cross|first4=Tom|last5=Culloty|first5=Sarah|last6=Ekaratne|first6=Suki|last7=Furness|first7=Bob|last8=Mulcahy |first8=Maire|last9=Thetmeyer|first9=Helmut|date=2009|title=Aquaculture: The Ecological Issues|publisher=John Wiley & Sons|page=68|isbn=978-1444311259|url=https://books.google.com/books?id=304yeBTnjpYC&pg=PA68}}</ref>

==== Pursuit diving ====
[[File:African Penguin Skeleton.jpg|thumb|An [[African penguin]] skeleton, showing the sternal keel that makes the species a strong diver and swimmer]]
Pursuit diving exerts greater pressures (both evolutionary and physiological) on seabirds, but the reward is a greater area in which to feed than is available to surface feeders. Underwater [[Marine propulsion|propulsion]] is provided by wings (as used by penguins, auks, [[diving petrel]]s and some other species of petrel) or [[Bird feet and legs|feet]] (as used by cormorants, [[grebe]]s, [[loon]]s and several types of fish-eating [[duck]]s). Wing-propelled divers are generally faster than foot-propelled divers.<ref name="Burger" /> The use of wings or feet for diving has limited their utility in other situations: loons and grebes walk with extreme difficulty (if at all), penguins cannot fly, and auks have sacrificed flight efficiency in favour of diving. For example, the [[razorbill]] (an Atlantic auk) requires 64% more energy to fly than a petrel of equivalent size.<ref name="Auk">Gaston, Anthony J.; Jones, Ian L. (1998). ''The Auks'', Oxford University Press, Oxford, {{ISBN|0-19-854032-9}}</ref> Many [[shearwater]]s are intermediate between the two, having longer wings than typical wing-propelled divers but heavier wing loadings than the other surface-feeding [[procellariidae|procellariids]], leaving them capable of diving to considerable depths while still being efficient long-distance travellers. The [[short-tailed shearwater]] is the deepest diver of the shearwaters, having been recorded diving below {{convert|70|m|ft}}.<ref>{{cite journal|author1=Weimerskirch, H. |author2=Cherel, Y. |year=1998|title= Feeding ecology of short-tailed shearwaters: breeding in Tasmania and foraging in the Antarctic? |journal=Marine Ecology Progress Series |volume=167|pages= 261–274|doi=10.3354/meps167261|bibcode=1998MEPS..167..261W |doi-access=free }}</ref>

Some albatross species are also capable of limited diving, with [[light-mantled sooty albatross]]es holding the record at {{convert|12|m|ft|sigfig=1}}.<ref>{{cite journal|author1=Prince, P. A. |author2=Huin, N. |author3=Weimerskirch, H. |year=1994|title=Diving depths of albatrosses|journal=Antarctic Science |volume=6|issue=3|pages= 353–354|doi=10.1017/S0954102094000532|bibcode=1994AntSc...6..353P|s2cid=129728675 }}</ref> Of all the wing-propelled pursuit divers, the most efficient in the air are the albatrosses, and they are also the poorest divers. This is the dominant guild in polar and subpolar environments, but it is energetically inefficient in warmer waters. With their poor flying ability, many wing-propelled pursuit divers are more limited in their foraging range than other guilds.<ref name="Ulanski">{{cite book |last1=Ulanski|first1=Stan|date=2016|title=The California Current: A Pacific Ecosystem and Its Fliers, Divers, and Swimmers|publisher=UNC Press Books|page=99|isbn=978-0070294219|url=https://books.google.com/books?id=iWM3CwAAQBAJ&pg=PT99}}</ref>

==== Plunge diving ====
[[Gannet]]s, [[booby|boobies]], [[tropicbird]]s, some terns, and [[brown pelican]]s all engage in plunge diving, taking fast-moving prey by diving into the water from flight. Plunge diving allows birds to use the energy from the momentum of the dive to combat natural buoyancy (caused by air trapped in plumage),<ref>{{cite journal|author1=Ropert-Coudert, Y. |author2=Grémillet, D. |author3=Ryan, P. |author4=Kato, A. |author5=Naito, Y. |author6=Le Maho, Y. |year=2004|title= Between air and water: the plunge dive of the Cape Gannet ''Morus capensis''|journal=Ibis |volume=146 |issue=2 |pages= 281–290|doi=10.1111/j.1474-919x.2003.00250.x}}</ref> and thus uses less energy than the dedicated pursuit divers, allowing them to utilise more widely distributed food resources, for example, in impoverished [[tropics|tropical]] seas. In general, this is the most specialised method of hunting employed by seabirds; other non-specialists (such as gulls and skuas) may employ it but do so with less skill and from lower heights. In brown pelicans, the skills of plunge diving take several years to fully develop—once mature, they can dive from {{convert|20|m|ft|abbr=on}} above the water's surface, shifting the body before impact to avoid injury.<ref name ="elliot">{{ cite book | last=Elliot | first=A. | year=1992 | chapter=Family Pelecanidae (Pelicans) | editor1-last=del Hoyo | editor1-first=J. | editor2-last=Elliott | editor2-first=A. | editor3-last=Sargatal | editor3-first=J. | title=Handbook of the Birds of the World | volume=1: Ostrich to Ducks | place=Barcelona, Spain | publisher=Lynx Edicions | isbn=84-87334-10-5 | pages=290–311 | chapter-url=https://archive.org/details/handbookofbirdso0001unse/page/290/mode/1up | chapter-url-access=registration }}</ref>

It may be that plunge divers are restricted in their hunting grounds to clear waters that afford a view of their prey from the air.<ref>Ainley, D. G. (1977) "Feeding methods in seabirds: a comparison of polar and tropical nesting communities in the eastern Pacific Ocean". In: Llano, G. A. (Ed.). ''Adaptations within Antarctic ecosystems''. Smithsonian Inst. Washington D.C., pp. 669–685</ref> While they are the dominant [[Guild (ecology)|guild]] in the tropics, the link between plunge diving and [[water clarity]] is inconclusive.<ref>{{cite journal|author1=Haney, J. C.  |author2=Stone, A. E.  |name-list-style=amp |year=1988|title=Seabird foraging tactics and water clarity: Are plunge divers really in the clear?|journal=Marine Ecology Progress Series |volume=49|pages= 1–9|doi=10.3354/meps049001|bibcode=1988MEPS...49....1H  |doi-access=free}}</ref> Some plunge divers (as well as some surface feeders) are dependent on [[dolphin]]s and [[tuna]] to push shoaling fish up towards the surface.<ref name="AU">{{cite journal|author1=Au, D. W. K.  |author2=Pitman, R. L.  |name-list-style=amp |year=1986|title= Seabird interactions with Dolphins and Tuna in the Eastern Tropical Pacific|journal=Condor|volume=88|pages= 304–317|url=http://sora.unm.edu/sites/default/files/journals/condor/v088n03/p0304-p0317.pdf|doi=10.2307/1368877|issue=3|jstor=1368877 }}</ref>

==== Kleptoparasitism, scavenging and predation ====
This catch-all category refers to other seabird strategies that involve the next [[trophic level]] up. [[Kleptoparasitism|Kleptoparasites]] are seabirds that make a part of their living stealing food of other seabirds. Most famously, [[frigatebird]]s and [[skua]]s engage in this behaviour, although gulls, terns and other species will steal food opportunistically.<ref>{{cite journal|author1=Schnell, G. |author2=Woods, B. |author3=Ploger B. |year=1983|title=Brown Pelican foraging success and kleptoparasitism by Laughing Gulls|journal=Auk |volume=100|issue=3 |pages=636–644|doi=10.1093/auk/100.3.636 }}</ref> The [[nocturnal animal|nocturnal]] nesting behaviour of some seabirds has been interpreted as arising due to pressure from this aerial piracy.<ref>Gaston, A. J.; Dechesne, S. B. C. (1996). Rhinoceros Auklet (''Cerorhinca monocerata''). In ''The Birds of North America, No. 212'' (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.</ref> Kleptoparasitism is not thought to play a significant part of the diet of any species, and is instead a supplement to food obtained by hunting.<ref name="Burger" /> A study of [[great frigatebird]]s stealing from [[masked booby|masked boobies]] estimated that the frigatebirds could at most obtain 40% of the food they needed, and on average obtained only 5%.<ref>{{cite journal|author1=Vickery, J.  |author2=Brooke, M.  |year=1994|title=The kleptoparasitic interactions between Great Frigatebirds and Masked Boobies on Henderson Island, South Pacific |journal=Condor |volume=96|pages=331–340|doi=10.2307/1369318|issue=2|jstor=1369318 |s2cid=8846837 }}</ref> Many species of gull will feed on seabird and sea mammal [[carrion]] when the opportunity arises, as will [[giant petrel]]s. Some species of albatross also engage in scavenging: an analysis of regurgitated [[squid]] beaks has shown that many of the squid eaten are too large to have been caught alive, and include mid-water species likely to be beyond the reach of albatrosses.<ref>{{cite journal|author1=Croxall, J. P.  |author2=Prince, P. A.  |name-list-style=amp |year=1994|title=Dead or alive, night or day: how do albatrosses catch squid?|journal=Antarctic Science |volume=6|pages= 155–162|doi=10.1017/S0954102094000246|issue=2|bibcode=1994AntSc...6..155C|s2cid=86598155 }}</ref> Some species will also feed on other seabirds; for example, gulls, skuas and pelicans will often take eggs, chicks and even small adult seabirds from nesting colonies, while the giant petrels can kill prey up to the size of small penguins and seal pups.<ref>{{cite journal|last1=Punta |first1=G. |last2=Herrera |first2=G. |year=1995|title=Predation by Southern Giant Petrels ''Macronectes giganteus'' on adult Imperial Cormorants ''Phalacrocorax atriceps''|journal=Marine Ornithology |volume=23|pages= 166–167 |url=http://www.marineornithology.org/PDF/23_2/23_2_9.pdf}}</ref>