Tuatara: Volume 8, Issue 2, May 1960
Identification of New Zealand Gulls and Terns
Identification of New Zealand Gulls and Terns
The gulls and terns are together a well-defined suborder, broadly divisible into the two families Laridae and Sternidae. There are distinctive tropical representatives which are cosmopolitan, and a complex of more differentiated forms in the temperate and sub-polar zones of both hemispheres. Several of the northern forms are transequatorial migrants and occur as non-breeders in the southern hemisphere. None of the New Zealand breeding forms is strongly endemic, although Sterna striata and Sterna albistriata are not known to breed elsewhere.
Because of the distinctive juvenile, subadult, summer adult and winter adult plumages, it is not practicable to present identification data in a single key. The method here followed is to give the salient points of field identification for each phase of each species, and to provide enough diagrammatic figures to emphasise these.
We are concerned with only three species of this family and no stragglers.
|(a)||Southern Black-backed Gull, Kelp Gull, Dominican Gull (Larus dominicanus), (Fig. 1)|
|Adults (bill of male slightly heavier than that of female): Body plumage entirely white except wings and mantle, which are black above, practically all the feather of the posterior series tipped with white, forming a posterior white band. Bill yellow with red patch at the angle of the mandible, eyelid orange or red, iris white, feet olive-green to chrome yellow according to season and local feeding habits. A young bird in its first winter has a black bill, dark brown feet, and is entirely mottled and barred, with a heavy grey-brown pattern over the whole plumage. This becomes whiter over the body plumage with seasonal wear and successive moults until the normal adult condition is attained within three years.|
|(b)||Red-billed Gull (Larus novaehollandiae scopulinus), (Figs. 2, 3)|
|Adult: Entire body plumage white, wings pearly grey on the upper surface with the distinctive black and white terminal markings shown in the figure. Bill, feet and eyelid coral red, iris white. The young bird in its first winter has bill and feet brownish, some brown spots on the shoulder soon lost by wear, and|
|more persistent brownish blotches subterminally on the secondaries. In the second winter bills and feet are a dull lifeless red. and the age of a young bird after this can only be estimated by observing the time of the annual wing moult, which is earlier in immature birds than in adults|
|(c)||Black-billed Gull (Larus bulleri), (Figs. 4, 5)|
|Although superficially very like the Red-billed Gull, this species is actually less compact and has the structure, habits and basic markings of the small hooded gulls of the northern hemisphere, although it does not develop the dark hood of those species. Adult plumage is entirely white except for the pearly grey upper wings with the distinctive markings shown in Fig. 5. Bill black, feet blackish red. iris white. Immature birds in their first winter have pale pink bills and feet, and during their second year these pass through a bright red phase before the bill becomes black. The temporary brownish markings on immature wings are similar to those described for the Red-billed Gull.|
In distinguishing the above two small Gulls, it is roughly correct to say that the young of the Red-billed Gull has a black bill, and the young of the Black-billed Gull has a red bill. There are slight differences in stance and flight that become more apparent after careful field study.
Identification here is more difficult, for not only are there the same age and seasonal plumage phases as found in Gulls, but there is also the vagrant occurrence of northern hemisphere and tropical Terns, mainly during the southern summer.
|(a)||Caspian Tern (Sterna caspia), (Fig. 9.)|
|The largest of the breeding Terns in New Zealand. Bill red at all ages and seasons, feet black. Body plumage all white except for grey upper wings and outer tail feathers. The tail is relatively short and only moderately forked. The young and adults in winter lose the black cap. which is replaced by white feathers on the forehead and crown, leaving the dark patch only behind the eye and on the nape.|
|(b)||White-fronted Tern (Sterna striata), (Fig. 8)|
|The commonest Tern in New Zealand, present throughout the year, although a large proportion of young birds appear to migrate to Australia. In breeding adults the bill is black, feet reddish black. Body plumage, including tail, pure white, wings pearly grey above. Young birds in first plumage have variable mottling on the shoulders and a mottled pattern of black and white on the crown behind the eye. In wintering adults the black cap recedes with the replacement by white feathers, producing the same general appearance as in the young.|
|(c)||Black-fronted Tern (Sterna albistriata), (Fig. 7)|
|This is probably a local representative of the Marsh Tern. Sterna hybrida. Adults in breeding plumage have grey plumage relieved only by a black cap. a white streak along the cheek, and a white rump. Bill and feet orange. In winter the adult head becomes mottled and this applies also to first winter|
|young, which are paler in body colour with black bills and feet. As Black-fronted Terns are known to breed only on riverbeds some distance inland, they may be more readily identified in such localities. Many, however, spend the winter months at sea.|
|(d)||Fairy Tern (Sterna nereis), (Fig. 6)|
|This must be accounted as the rarest of the breeding Terns, being known from nesting records only in North Auckland in small numbers. Adult body plumage mainly white but with pearly grey upper wings and a suffusion of pale pearl-grey on the underparts. Black head markings as shown in Fig. 6, bill and feet bright yellow. In winter plumage and immature birds the bill and feet are black, and the dark area on the head restricted to a patch at the nape.|
|(e)||Subantarctic Tern (Sterna vittata)|
|Breeding from Stewart Island south throughout the Subantarctic are dark purplish-grey Terns with white streaks below the black cap, pure white tails and red bills and feet. They have not been recorded as wintering north of Foveaux Strait.|
|(f)||Arctic Tern (Sterna paradisaea)|
|This northern hemisphere breeder is likely to occur in small numbers along the coasts during the southern summer. It is then in winter plumage with irregular blackish cap behind the eye and black bill and feet, which could be crimson if the bird were coming into breeding condition in February or March. The best distinguishing feature is the thin black edge to the long streamers which form the outer tail feathers.|
|(g)||White-winged Black Tern (Chlidonias leucopterus), (Figs. 10, 11)|
|An Asiatic breeder migrating to the southern hemisphere. There have been numerous New Zealand records, mainly in the variable winter plumage figured by Fleming (Notornis, Vol. 6, No. 3, p. 71, 1955) and reproduced here (Figs. 10, 11). The rarely seen full plumage is unmistakable, with the body almost jet black and the wings greyish white above and white below.|
Other tropical Terns that have been recorded as stragglers are:
- Sooty Tern (Sterna fuscata)
- Common Noddy (Anous stolidus)
- White-capped Noddy (Anous minutus)
- White Tern (Gygis alba)
- Grey Ternlet (Procelsterna cerulea)
- Crested Tern (Sterna bergii); and
- Little Tern (Sterna albifrons) (sight record).
Another related family not dealt with in this review comprise the Skuas (Stercorariidae), comprising two southern forms of the Great Skua and two northern Skuas on migration.
ORNITHOLOGICAL SOCIETY OF N.Z., 1953 - Checklist of N.Z. Birds.
OLIVER. W. R. B., 1955 -New Zealand Birds (2nd ed.).