Laridae Gulls, Terns, and Skimmers
Version: 1.0 — Published March 4, 2020
Introduction
The Laridae are the most familiar charadriiform birds of every shore. Active, obvious, and seldom shy, they are sometimes in our lives even more than we would like. They can be divided by what they eat: Gulls generally eat any animal they can swallow, dead or alive, and they gather their food with an astonishing opportunism and ingenuity; terns mostly eat fish that they dive for, and they stay out of each other’s way in loose foraging aggregations; and skimmers use their highly specialized bills to snag their prey from the surface of calm water, often in gracefully coordinated bands. Larids lay their eggs on sandy beaches, atop precarious cliff ledges, and even in trees, and the precocial young are fed at home until they fledge.
Habitat
Larids occupy a wider range of habitats than the colloquial name “seagull” would suggest. While most species live in coastal areas, some are deep-ocean pelagic species for most of the year and others live far inland, mostly near water but also in some extremely xeric environments that are within a daily commute to water. Gulls are most diverse in the temperate zone, occupying the greatest range of habitats there, from pack ice to alpine tarns, and from city parks to agricultural fields. Terns and skimmers are most diverse in the tropics, and there they occupy all aquatic habitats, from remote ocean very far from land to coastal lagoons and rivers.
Diet and Foraging
Gulls feed on a wide variety of items, especially crustaceans and insects as well as fish, mammals, and birds. They will eat their prey alive or dead, with many taking advantage of mammal, bird, and fish carcasses, and the larger gulls are effective predators, not only on eggs and chicks, but also on adult birds of considerable size. Although gulls are largely diurnal, one species, the Swallow-tailed Gull Creagrus furcatus, is highly specialized and forages at night on squid. Most terns feed primarily on fish and aquatic invertebrates that are caught by plunge-diving into the water. Skimmers have a highly specialized mode of feeding, flying steadily low over still waters, skimming their elongated lower bill in the water and snapping up any small fish or crustaceans that touch it.
Breeding
Most larid species are colonial or semi-colonial; the need for nesting areas relatively free of vegetation and protected from predators (usually on islands) means nesting space is usually limited and breeding areas are crowded. A very small territory around the nest is defended against conspecifics, which, in gulls, are one of the greatest threats to successful nesting. Most colonies are defended by group defense, and potential predators in the colony are met with aggressive dive-bombing, including alarm-calling and defecating upon and striking the intruder. Most species nest on the ground, with nests consisting of simple scrapes, filled, in most gulls species, with a loose nest of twigs, grass, and feathers. Some species nest on cliff ledges and in niches in rock or on floating mats of marsh vegetation. Others nest in trees; female white terns (Gygis) uniquely balance their single eggs on a sturdy branch in a tree with no nest at all. Larids are monogamous, with both parents assisting in incubation and chick provisioning. The precocial chicks hatch after 19 to 40 days of incubation and are generally capable of their own thermoregulation after the first few days, but they must be fed by their parents all the way up to leaving the colony four to six weeks after hatching.
Conservation Status
While many gull species are extremely abundant, 22 species (nearly 22%) of larids face some conservation concern (11 NT, 6 VU, 4 EN, 1 CR). The critically endangered Chinese Crested Tern Thalasseus bernsteini numbers at most 40 mature adults spread between two colonies, and continues to decline as a result of habitat loss and egg collection. Many other declining species of gulls and terns are the victims of habitat destruction and degradation. The Ivory Gull Pagophila eburnea, a distinctive symbol of the high Arctic, appears to be experiencing rapid population declines, and these declines are likely associated with rapidly disappearing sea ice. It may well be that the Ivory Gull will be one of the first victims of global climate change.
Systematics History
Laridae is part of the suborder Lari of Charadriiformes. Recent molecular phylogenetic studies suggest that, within Lari, Laridae appears to be sister to the clade containing Stercorariidae and Alcidae (Paton & Baker 2006, Baker et al. 2007a, Fain & Houde 2007, Pereira & Baker 2010). The limits of the family Laridae have varied substantially over the years, from encompassing the gulls, terns, skimmers, and skuas to the other extreme of separating out all of these groups into their own respective families. This latter approach would be attractive, as the diversity of ecology and morphology in this family is considerable. The most recent study of the group found the tern genera Anous and Gygis to be sister to both gulls and the other terns (Baker et al. 2007a), but this contrasted with other studies that instead recovered a monophyletic tern clade (Bridge et al. 2005, Pons et al. 2005). The relationship of skimmers (Rynchops) to the rest of Laridae has also differed across studies, with the skimmers variously appearing as sister to the gulls (Baker et al. 2007a, Pereira & Baker 2010), to terns (Paton & Baker 2006, Fain & Houde 2007), or to both gulls and terns (Sibley & Ahlquist 1990, Ericson et al. 2003a). Further study will no doubt clarify these relationships, but it seems preferable for now to retain each of the clades that have been recognized recently as separate subfamilies here.
Conservation Status
Least Concern |
72%
|
---|---|
Near Threatened |
8%
|
Vulnerable |
9%
|
Endangered |
4%
|
Critically Endangered |
1%
|
Extinct in the Wild |
0%
|
Extinct |
0%
|
Not Evaluated |
0%
|
Data Deficient |
0%
|
Unknown |
6%
|
Data provided by IUCN (2023) Red List. More information