Terns, Gulls, and Skuas (Family Laridae)
David Thompson, Franz Smith, and Taoho Patuawa
General Description
Terns, gulls, and skuas are members of a large group of seabirds of the order Charadriiformes. Within this order, the family Laridae contains 98 species worldwide and the family Stercorariidae eight species in total. The morphology of these seabirds varies greatly with smaller and relatively thinner gulls and terns to the larger and more robust skuas, jaegers and some gulls and terns.
The terns and noddies are cosmopolitan seabirds characterised by narrowly pointed wings and long, pointed bills. The birds are primarily marine, feeding in inshore waters, while some species forage in both marine and fresh waters and others are more pelagic and offshore. Feeding is largely accomplished by surface plunging or skimming from the surface. Diet is composed primarily of small fish, but may also take crustaceans, molluscs, and insects. Some species are nocturnal or crepuscular. Species can be highly gregarious when feeding, roosting, and breeding. Pairs are monogamous, with some degree of persistence, typically formed after three to four years of age. Seasonal breeding colonies in several species can number in thousands or tens of thousands. Clutch sizes are one to three in most species and incubation periods can be between three and five weeks. Chicks are semi-precocial, and in ground-nesting species, chicks can leave the nest after a week. Fledglings of most species are dependent on parents for food for up to four months. The genus Sterna, the sea terns, is represented by 33 species worldwide, with six species breeding in New Zealand. Characteristics of the medium-sized Sterna from the southern hemisphere suggest a major radiation from a common ancestor. The genus Anous, the dark noddies, has three species, two of which breed within New Zealand. The genus Gygis, is represented by two species, one of which, the white tern, G. alba, breeds within New Zealand. Similarly, the genus Procelsterna contains a single species, the grey ternlet, P. cerulea, which breeds in New Zealand.
Gulls represent a group of medium to large coastal birds which are opportunistic predators and scavengers of both land and sea. The endemic black-billed gull, Larus bulleri, breeds on inland and braided rivers of the North and South islands. Life-history characteristics, such as the age of first breeding, adult and juvenile survival, and site fidelity, of this species are poorly known. The southern black-backed gull, Larus dominicanus, has large breeding colonies of up to 5000 pairs within New Zealand-colonies in Australia, Antarctica, and other Southern Ocean islands are much smaller. Some colonies breed on offshore islands as well as in riverbeds. The red-billed gull, Larus scopulinus, a New Zealand endemic, breeds widely on offshore islands of the three main islands, with colonies present on the Three Kings Islands and the Auckland Islands, Chatham Island and Campbell Island, and The Snares. The subantarctic populations are sometimes considered a separate subspecies, coincidens.
Skuas and jaegers are medium to large in size, and are opportunistic predators and scavengers, notorious for being kleptoparasites. The IUCN recognises eight species in two genera: Catharacta (skuas) and Stercorarius (jaegers). All but one species of skua breeds within the southern hemisphere, while jaegers breed at high latitudes in the northern hemisphere. When not breeding, species are widely dispersed in pelagic and coastal waters and are highly migratory. Their feeding occurs both on land and at sea, with a wide variety of dietary items, including carrion, small mammals, eggs and young of other seabirds, landbirds, and fish, crustaceans, and molluscs. They are also known to feed on discards and garbage. While breeding, skuas are extremely territorial and aggressive defenders of nests. Normally two eggs per clutch are laid and incubated for approximately a month. Chicks are precocial and fed by both parents for an extended period, up to seven weeks after fledgling. There have been five species recorded in the New Zealand region, but only the brown skua, Catharacta lonnbergi, breeds in the region. All others are considered migrants to the region.
The breeding species diversity and endemism for the Laridae and Stercorariidae in New Zealand include three of fifty-one species of gulls worldwide (6%), two of which are endemic, ten species of breeding terns and related species of forty-seven worldwide (21%), one of which is endemic, and one non-endemic, and one breeding species of skua of the eight species worldwide (13%).
Status
The black-fronted tern, Sterna albostriata, an endemic species, is classified as "endangered" according to IUCN criteria, breeding in South Island riverbeds, as is the black-billed gull. The New Zealand fairy tern, Sterna nereis davisae, is an endemic subspecies, which breeds only in Northland at Papakanui Spit (South Kaipara Head), and Mangawhai and Waipu estuaries, with the total New Zealand population in 1997-1999 about 25-30 birds (ie, about 8-10 breeding pairs), representing about a 50% population decline since 1970. The New Zealand white-fronted tern, Sterna striata striata, is an endemic subspecies breeding along the coasts of the North and South islands, and Stewart Island. This species and all other New Zealand species of gulls, terns and the brown skua are classified as "least concern" by the IUCN.
Key Locations
For the southern black-backed gull, key sites include Ashburton River, the Nelson Boulderbank, Mana Island, Matiu/Somes Island (Wellington Harbour), Sulphur Bay (Lake Rotorua), and Rangitoto Island. The black-billed gull has key sites in harbours of the North Island, such as the Kaipara and the Manukau harbours, and large riverbeds in the South Island, such as the Ashburton, Mataura, Oreti, and Waiau rivers.
Summary of Threats
One of the key threats for the species of gull and tern within New Zealand is the loss or disturbance of breeding habitat, particularly for species which breed along beaches and in riverbeds. Introduced predators at these sites can be responsible for mortality of both adults and chicks, serving as a direct threat to breeding colonies. Human activities such as the extraction of gravel and sand from riverbeds and beaches represent an indirect threat to breeding colonies. Weed encroachment on some colonies (such as those of the black-billed gull) has also been identified as a potential problem in lowland Canterbury riverbeds.
Typical Habitats
Gulls can be found in a variety of coastal and inland habitats, including lakes and rivers. Some species have also been known to widely disperse around the Southern Ocean.
State of Information
Aspects of the breeding biology, diet, and social organisation have been made for isolated locations (eg, Matiu/Somes Island, Wellington Harbour), although studies in other areas are lacking. Distribution and size of breeding colonies and movements are studied in the Canterbury and Nelson areas in the South Island, and the Bay of Islands and Whangarei in the North Island. It has been suggested that nationwide surveys for the black-backed gull are needed.
Significance for Maori
All species of tern are collectively referred to as "tara" by Maori, with the exception of the fairy tern which is called taraiti (that is, little tara). These birds were likened to persons of rank and status, due largely to the black caps that emphasise their head, which to Maori is tapu (or sacred). When a group of rangatira, of chiefs, were honoured, they were spoken of as being "he tahuna a tara" (a sandbank of tara) or "he kahui tara" (flock of tara).
Black-backed gulls are called "karoro" and are symbolic in being the bird that belongs to the shore. Being much larger and more assertive than their cousins the tarapunga (red-billed and black-billed gulls), the strong stance and harsh cries of the karoro were seen as a sign of the coast being in good health. It was often considered a bad omen to see karoro in a valley far inland. Tarapunga were seldom referred to in tradition or poetry, and were usually overlooked by the strength of the karoro and the beauty and grace of the tara.
Key References
Orbel, M. 2003. Birds of Aotearoa. A Natural and Cultural History. Reed Publishing. 198pp.
Taylor, G A. 2000. Action plan for seabird conservation in New Zealand. Part A. Threatened Seabirds. Threatened Species Occasional Publication No. 16. Department of Conservation, Wellington, New Zealand. 233pp.
Taylor, G A. 2000. Action plan for seabird conservation in New Zealand. Part B. Non-threatened Species. Threatened Species Occasional Publication No. 17. Department of Conservation, Wellington New Zealand. 435pp.
Table 6: Terns, Gulls (Family Laridae), and Skuas (Family Stercorariidae) in New Zealand
| Taxon | Common name | Breeding species | Endemic species |
|---|---|---|---|
| Family Laridae | |||
| Anous stolidus | Common noddy | 1 | 0 |
| Anous tenuirostris | White-capped noddy | 1 | 0 |
| Sterna albostriata | Black-fronted tern | 1 | 1 |
| Sterna caspia | Caspian tern | 1 | 0 |
| Sterna fuscata | Sooty tern | 1 | 0 |
| Sterna nereis davisae | New Zealand fairy tern | 1 | 1 |
| Sterna striata | White-fronted tern | 1 | 0 |
| Sterna vittata | Antarctic tern | 1 | 0 |
| Procelsterna cerulea | Grey ternlet | 1 | 0 |
| Gygis alba | White tern | 1 | 0 |
| Larus dominicanus | Southern black-backed gull | 1 | 0 |
| Larus bulleri | Black-billed gull | 1 | 1 |
| Larus scopulinus | Red-billed gull | 1 | 1 |
| 13 | 4 | ||
| Family Stercorariidae | |||
| Catharacta lonnbergi | Brown skua | 1 | 0 |
| 1 | 0 | ||
| Total | 14 | 4 |
Figure 25: Brown noddy Anous stolidus pileatus annual distribution.
Figure 26: Brown noddy Anous stolidus pileatus breeding.
Figure 27: Black-fronted tern Sterna albostriata annual distribution.
Figure 28: Black-fronted tern Sterna albostriata breeding.
Figure 29: New Zealand fairy tern Sterna nereis davisae breeding.