Laridae: Gulls, Terns and Skimmers
Gulls and terns are beach-lovers, most of which spend the bulk of their lives within sight of the land-water interface. This tends to put them in persistent contact with humanity, but overall they succeed at coexisting with development. Many gulls are opportunistic scavengers, a niche that presents seemingly endless growth opportunities in and around coastal communities of all sizes. In many urban areas, the largest gatherings of gulls are often at garbage dumps, the paradise of modern scavenging.
The other larids—which include terns and the similar but distinct noddies and skimmers—subsist primarily on small fish and other bite-sized aquatic life taken at the surface in graceful swooping dives. For many terns, the optimal foraging habitats are protected water bodies such as lagoons that serve as fish nurseries, ideally situated near small islands or sandbars that allow them to rest safely with minimal vigilance. The most specialized larids are the skimmers, which are unique in having a disproportionately long lower mandible adapted to skimming the surface for small fish, a foraging technique that works only in waters that are sheltered enough to remain consistently calm.
Several terns, most noddies, and a few gulls are pelagic. Many of these are rarely seen except during the breeding season, and spend the bulk of their lives in remote seas as yet unknown.
Taxonomy
As currently understood the Laridae comprises five subfamilies:
Rhynchopinae: Skimmers (3 species)
Gyginae: Fairy-terns (3 species)
Sterninae: Terns (41 to 44 species)
Anouinae: Noddies (5 to 8 species)
Larinae: Gulls (57 to 70 species)
The skimmers were traditionally classified as a separate family, but a series of genetic studies suggest that they are more closely related to terns, and that the noddies (which were formerly considered to be a subgroup of terns) are more closely related to the gulls.
Species-level classification is plagued by several sets of closely related forms that occur in different regions and rarely come into contact with one another. A few such cases of speciation in progress are probably unresolvable and require an arbitrary determination.
A prime example is the case of Cabot’s Tern (Thalasseus acuflavidus) and “Cayenne Tern” (eurygnathus), which are North and South American counterparts that differ in bill color and were traditionally considered separate species—or, more accurately, Cabot’s was classified as a subspecies of the Old World Sandwich Tern (sandvicensis), based on their distinctive yellow-tipped black bills, and the all-yellow-billed Cayenne was regarded as a different species. In recent decades, however, Cayenne and Cabot’s have been found hybridizing in the West Indies, which has shifted the consensus to regard them as a single species. At the same time, multiple lines of evidence have developed to distinguish Cabot’s from Sandwich sufficiently to persuade most authorities that they are separate species.
The general trend in the 2000s among larid taxonomists has been to acknowledge more diversity through the recognition of more forms as separate species. One of the best-known cases of ambiguous species delineation in the bird world is the Herring Gull complex, in which several forms are known to interbreed occasionally—but if all the interbreeding forms were considered conspecific the resulting agglomeration would include forms that occur together without interbreeding. What was once known as the Herring Gull has been reclassified as seven species: European Herring, Armenian, Yellow-legged, Caspian, American Herring, Vega, and Mongolian. The total rises to nine with the addition of two that were sometimes lumped in: Lesser Black-backed and Heuglin’s.
Conversely, some different-looking forms have been found to interbreed so freely that ornithologists have determined that they must be considered a single, highly variable species. For example, the “Iceland Gull” (glaucoides) and “Thayer’s Gull” (thayeri) differ outwardly and were traditionally considered separate species—and for many decades “Thayer’s” was classified as a subspecies of Herring Gull (which increases the Herring Gull complex to ten recognized species). An intermediate form, “Kumlien’s Gull” (kumlieni), interbreeds freely with both “Iceland” and “Thayer’s”, resulting in a spectrum of plumages. In 2018, the relevant taxonomic authorities unanimously agreed to reclassify the three forms as a single species, the Iceland Gull (Larus glaucoides).
The resulting count rests somewhere in the span of 109 to 129 species.
Black Skimmer (Rynchops niger)
African Skimmer (Rynchops flavirostris)
Indian Skimmer (Rynchops albicollis)
Common Fairy-Tern (Gygis candida)
Atlantic Fairy-Tern (Gygis alba)
Little Fairy-Tern (Gygis microrhyncha)
Sooty Tern (Onychoprion fuscatus)
Gray-backed Tern (Onychoprion lunatus)
Bridled Tern (Onychoprion anaethetus)
Aleutian Tern (Onychoprion aleuticus)
Little Tern (Sternula albifrons)
Least Tern (Sternula antillarum)
Yellow-billed Tern (Sternula superciliaris)
Australian Fairy Tern (Sternula nereis)
Peruvian Tern (Sternula lorata)
Saunders’s Tern (Sternula saundersi)
Damara Tern (Sternula balaenarum)
Large-billed Tern (Phaetusa simplex)
Gull-billed Tern (Gelochelidon nilotica)
Australian Tern (Gelochelidon macrotarsa)
Caspian Tern (Hydroprogne caspia)
Black Tern (Chlidonias niger)
White-winged Tern (Chlidonias leucopterus)
Whiskered Tern (Chlidonias hybrida)
Black-fronted Tern (Chlidonias albostriatus)
American Royal Tern (Thalasseus maximus)
African Royal Tern (Thalasseus albididorsalis)
Greater Crested Tern (Thalasseus bergii)
Sandwich Tern (Thalasseus sandvicensis)
Cabot’s Tern (Thalasseus acuflavidus)
“Cabot’s Tern” (T. a. acuflavidus)
“Cayenne Tern” (T. a. eurygnathus)
Elegant Tern (Thalasseus elegans)
Lesser Crested Tern (Thalasseus bengalensis)
Chinese Crested Tern (Thalasseus bernsteini)
Roseate Tern (Sterna dougallii)
White-fronted Tern (Sterna striata)
Black-naped Tern (Sterna sumatrana)
South American Tern (Sterna hirundinacea)
Common Tern (Sterna hirundo)
“Common Tern” (S. h. hirundo)
“Siberian Tern” (S. h. longipennis)
Antarctic Tern (Sterna vittata)
“Antarctic Tern” (S. v. vittata)
“South Georgia Tern” (S. v. georgiae)
Arctic Tern (Sterna paradisaea)
Forster’s Tern (Sterna forsteri)
Snowy-crowned Tern (Sterna trudeaui)
Black-bellied Tern (Sterna acuticauda)
River Tern (Sterna aurantia)
White-cheeked Tern (Sterna repressa)
Kerguelen Tern (Sterna virgata)
“Brown Noddy” (A. s. stolidus)
“Galápagos Noddy” (A. s. galapagensis)
Lesser Noddy (Anous tenuirostris)
“Atlantic Black Noddy” (A. m. americanus)
“Pacific Black Noddy” (A. m. minutus)
“Hawaiian Noddy” (A. m. melanogenys)
Swallow-tailed Gull (Creagrus furcatus)
Little Gull (Hydrocoloeus minutus)
Ross’s Gull (Rhodostethia rosea)
Black-legged Kittiwake (Rissa tridactyla)
Red-legged Kittiwake (Rissa brevirostris)
Ivory Gull (Pagophila eburnea)
Saunders’s Gull (Saundersilarus saundersi)
Slender-billed Gull (Chroicocephalus genei)
Bonaparte’s Gull (Chroicocephalus philadelphia)
Black-headed Gull (Chroicocephalus ridibundus)
Brown-headed Gull (Chroicocephalus brunnicephalus)
Gray-hooded Gull (Chroicocephalus cirrocephalus)
Gray-headed Gull (Chroicocephalus poiocephalus)
Hartlaub’s Gull (Chroicocephalus hartlaubii)
Red-billed Gull (Chroicocephalus scopulinus)
Silver Gull (Chroicocephalus novaehollandiae)
Black-billed Gull (Chroicocephalus bulleri)
Andean Gull (Chroicocephalus serranus)
Brown-hooded Gull (Chroicocephalus maculipennis)
Gray Gull (Leucophaeus modestus)
Dolphin Gull (Leucophaeus scoresbii)
Laughing Gull (Leucophaeus atricilla)
Franklin’s Gull (Leucophaeus pipixcan)
Lava Gull (Leucophaeus fuliginosus)
Pallas’s Gull (Ichthyaetus ichthyaetus)
Relict Gull (Ichthyaetus relictus)
Mediterranean Gull (Ichthyaetus melanocephalus)
Audouin’s Gull (Ichthyaetus audouinii)
White-eyed Gull (Ichthyaetus leucophthalmus)
Sooty Gull (Ichthyaetus hemprichii)
Pacific Gull (Larus pacificus)
Belcher’s Gull (Larus belcheri)
Olrog’s Gull (Larus atlanticus)
Black-tailed Gull (Larus crassirostris)
Heermann’s Gull (Larus heermanni)
Ring-billed Gull (Larus delawarensis)
Short-billed Gull (Larus brachyrhynchus)
Common Gull (Larus canus)
“European Gull” (L. c. canus)
“Russian Gull” (L. c. heinei)
“Kamchatka Gull” (L. c. kamtschatschensis)
Western Gull (Larus occidentalis)
Yellow-footed Gull (Larus livens)
Kelp Gull (Larus dominicanus)
“Kelp Gull” (L. d. dominicanus)
“Antarctic Gull” (L. d. austrinus)
“Subantarctic Gull” (L. d. judithae)
“Cape Gull” (L. d. vetula)
“Madagascan Gull” (L. d. melisandae)
Glaucous Gull (Larus hyperboreus)
European Herring Gull (Larus argentatus)
Caspian Gull (Larus cachinnans)
Lesser Black-backed Gull (Larus fuscus)
“Lesser Black-backed Gull” (L. f. graellsii)
“Baltic Gull” (L. f. fuscus)
Heuglin’s Gull (Larus heuglini)
“Heuglin’s Gull” (L. h. heuglini)
“Taimyr Gull” (L. h. taimyrensis)
“Steppe Gull” (L. h. barabensis)
Great Black-backed Gull (Larus marinus)
Yellow-legged Gull (Larus michahellis)
“Atlantic Yellow-legged Gull” (L. m. atlantis)
“Cantabrican Yellow-legged Gull” (L. m. ssp. nova)
“Mediterranean Yellow-legged Gull” (L. m. michahellis)
Armenian Gull (Larus armenicus)
California Gull (Larus californicus)
American Herring Gull (Larus smithsonianus)
Glaucous-winged Gull (Larus glaucescens)
Iceland Gull (Larus glaucoides)
“Thayer’s Gull” (L. g. thayeri)
“Kumlien’s Gull” (L. g. kumlieni)
“Iceland Gull” (L. g. glaucoides)
References
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Text © Russell Fraker / February 14, 2022