Editing Seabird (section)

== Classification ==
There exists no single definition of which groups, families and species are seabirds, and most definitions are in some way arbitrary. Elizabeth Shreiber and Joanna Burger, two seabird scientists, said, "The one common characteristic that all seabirds share is that they feed in [[seawater|saltwater]]; but, as seems to be true with any statement in biology, some do not."<ref name="Burger">Schreiber, Elizabeth A. and Burger, Joanne (2001) ''Biology of Marine Birds''. Boca Raton: CRC Press, {{ISBN|0-8493-9882-7}}</ref> However, by convention, all of the [[penguin|Sphenisciformes (penguins)]], all of the [[tropicbird|Phaethontiformes (tropicbirds)]], all of the [[Procellariiformes]] ([[albatross]]es and [[petrel]]s), all of the [[Suliformes]] ([[gannet]]s, [[Booby|boobies]], [[frigatebird]]s, and [[cormorant]]s) except the [[darter]]s, one family of the [[Pelecaniformes]] ([[pelican]]s), and some of the [[Charadriiformes]] ([[gull]]s, [[skua]]s, [[tern]]s, [[auk]]s, and [[Skimmer (bird)|skimmer]]s) are classified as seabirds. The [[phalarope]]s are usually included as well, since although they are [[wader]]s ("shorebirds" in North America), two of the three species ([[Red Phalarope|red]] and [[Red-necked Phalarope|red-necked]]) are oceanic for nine months of the year, crossing the equator to feed pelagically.<ref name="Rubega">{{cite journal |url= https://birdsoftheworld.org/bow/species/renpha/cur/introduction |title=Red-necked Phalarope (Phalaropus lobatus), version 1.0|last1=Rubega|first1=Margaret A. |last2= Schamel| first2= Douglas |last3= Tracy|first3= Diane M. |date=March 4, 2020 |journal=Birds of the World |publisher=Cornell Lab of Ornithology |doi=10.2173/bow.renpha.01|s2cid=216464615|access-date=March 26, 2021|url-access=subscription}}</ref><ref name="Tracy">{{cite journal |url= https://birdsoftheworld.org/bow/species/redpha1/cur/introduction |title= Red Phalarope (Phalaropus fulicarius), version 1.0|last1=Tracy|first1= Diane M.|last2= Schamel| first2= Douglas |last3=Dale|first3=James|date=March 4, 2020 |journal=Birds of the World |publisher=Cornell Lab of Ornithology |doi= 10.2173/bow.redpha1.01|s2cid= 216176285|access-date=March 26, 2021|url-access=subscription}}</ref>

[[Loon]]s and [[grebe]]s, which nest on lakes but winter at sea, are usually categorized as water birds, not seabirds. Although there are a number of [[Merginae|sea ducks]] in the family [[Anatidae]] that are truly marine in the winter, by convention they are usually excluded from the seabird grouping. Many [[heron]]s and [[wader]]s (or shorebirds), such as [[crab-plover]]s, are also highly marine, living on the sea's edge (coast), but are also not treated as seabirds. Fish-eating birds of prey, such as [[sea eagle]]s and [[osprey]]s, are also typically excluded, however tied to marine environments they may be.<ref name="Brooke511">{{cite book |last=Brooke |first=Michael |date=2018 |title=Far From Land: The Mysterious Lives of Seabirds |location=Princeton |publisher=Princeton University Press |pages=5–11 |isbn=978-0-691-17418-1}}</ref> Some birds, such as [[darter]]s and [[anhinga]]s, are primarily found in freshwater habitats, but may occasionally venture into marine or coastal areas as well;<ref>{{cite web | first=Laura | last=Howard | date=2003 | title=Anhingidae | url=https://animaldiversity.org/accounts/Anhingidae/ | website=Animal Diversity Web | access-date=13 January 2025}}</ref><ref>{{cite web | title=Anhinga Life History | url=https://www.allaboutbirds.org/guide/Anhinga/lifehistory | website=All About Birds | access-date=13 January 2025}}</ref> such birds are generally not considered to be seabirds.

German ornithologist [[Gerald Mayr]] defined the "core waterbird" clade [[Aequornithes]] in 2010. This lineage gives rise to the [[Procellariiformes]], [[Sphenisciformes]], [[Suliformes]], [[Pelecaniformes]], [[Ciconiiformes]] (not seabirds), and [[Gaviiformes]] (not seabirds).<ref name="Burleigh">{{Cite journal|last1=Burleigh |first1=J.G.|display-authors=et al |date=March 2015 |title=Building the avian tree of life using a large-scale, sparse supermatrix |journal=Molecular Phylogenetics and Evolution |volume=84 |pages=53–63 |pmid= 25550149|doi=10.1016/j.ympev.2014.12.003|bibcode=2015MolPE..84...53B }}</ref> The [[tropicbird]]s ([[Phaethontiformes]]) are part of the [[Eurypygimorphae]] lineage, which is [[sister group|sister]] to the Aequornithes;<ref>{{cite journal | last1 = Jarvis | first1 = E.D. | display-authors = etal   | year = 2014 | title = Whole-genome analyses resolve early branches in the tree of life of modern birds | journal = Science | volume = 346 | issue = 6215| pages = 1320–1331 | doi=10.1126/science.1253451 | pmid=25504713 | pmc=4405904| bibcode = 2014Sci...346.1320J }}</ref> this clade also includes the non-seabird [[Eurypygiformes]] ([[kagu]] and [[sunbittern]]). The [[Charadriiformes]] are more distantly related to the other seabirds, being more closely related to the non-seabird [[Gruiformes]] ([[Rail (bird)|rails]] and [[Crane (bird)|cranes]]) and [[Opisthocomiformes]] ([[hoatzin]]) in the clade [[Gruae]].<ref name=Jarvis2014>{{cite journal | last1 = Jarvis | first1 = E.D. |display-authors=etal  | year = 2014 | title = Whole-genome analyses resolve early branches in the tree of life of modern birds | journal = Science | volume = 346 | issue = 6215| pages = 1320–1331 | doi=10.1126/science.1253451 | pmid=25504713 | pmc=4405904| bibcode = 2014Sci...346.1320J }}</ref>