| Black-legged Kittiwake | |
|---|---|
 | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Charadriiformes |
| Family: | Laridae |
| Genus: | Rissa |
| Species: | Rissa tridactyla |
The Black-legged Kittiwake (Rissa tridactyla), known simply as Kittiwake in Europe, is a strictly pelagic and highly gregarious gull.
Taxonomy[]
The Black-legged Kittiwake is one of two members of the genus Rissa, the other one being the far less common Red-legged Kittiwake (Rissa brevirostris). The name Rissa comes from the Icelandic name for this bird, Rita. Within the Larinae (gull) subfamily, the Kittiwakes form a clade with the Ivory Gull, Sabine's Gull, Ross's Gull, and the Swallow-tailed Gull.
Subspecies[]
Rissa tridactyla has two subspecies:
- R. t. tridactyla, the Atlantic subspecies, is the only gull that lacks a hind toe, as the name tridactyla (Ancient Greek for "three-toed") suggests;
- R. t. pollicaris, the Pacific subspecies, often has a normally developed hind toe (pollicaris comes from pollex, "thumb").
Description[]
Adult in flight, seen from above
A medium-small gull, the Kittiwake weighs about 400 g (14 oz) and measures 37-42 cm (14.5 - 16.5 in) in length and 93-105 cm (36.6 - 41.3 in) in wingspan. It has long, pointed wings, a rather large, rounded head, short, dark legs (rarely reddish or orange), and a short, slightly notched tail. Its eyes are large, black with a thin red eye-ring. The adult in breeding plumage has a white body, grey upperwings and mantle (paler on the inner primaries), solid black wingtips, thin white trailing edges on the wings, and a yellow bill. The winter plumage is similar, but with a grey hindneck and a crescent-shaped black ear-spot. The juvenile has a distinctive black "W-pattern" across the wings, a black tail-tip, a black ear-spot, and a black bill. Some juveniles have a black half-collar in winter. The Black-legged Kittiwake gets its adult plumage on the third year of its life. Pacific individuals (R. t. pollicaris) tend to have darker mantles and are, on average, slightly larger with a longer bill. The Atlantic subspecies shows a progressive increase in size from South to North, in accordance with Bergmann's rule. The hind toe, generally absent, is more frequently present in the Pacific population (about 50% of individuals) than in the Atlantic population (about 9%); when present, it reaches a greater length and is equipped with a more developed nail in the non-nominal subspecies.
Voice[]
The Black-legged Kittiwake is an extremely noisy bird, especially at nesting colonies. Nesting birds make various loud, nasal calls, the most common of which is a repeated "kitt-i-waake", hence the English name of the species.
Behaviour[]
Nesting colony
In summer, Kittiwakes gather in large colonies to nest on steep cliffs by the sea. The Black-legged Kittiwake shows peculiar behavioral and morphological adaptations associated with the adaptive strategy of colonial nesting in cliff environments. The cliff ledges that house the Kittiwake's nests are practically inaccessible to terrestrial predators. Moreover, due to the strong air currents that form along the vertical walls, approaching the nests is extremely difficult even for winged predators; on the other hand, it is carried out easily by the Kittiwakes, the most experienced flyers among the Larids, endowed with great maneuvering skills and able to perform extremely controlled and precise movements. When a predatory bird such as a larger Gull, Skua, or Corvid does manage close to the nests, it is possible to observe the breeding individuals stretch out their open beak forwards and then take off manifesting collective mobbing behavior, which is accompanied by very intense calls. Like many other seabirds, Kittiwakes are generally not afraid of humans. In winter, the Kittiwakes leave their nesting grounds for the high seas, rarely appearing inland.
Breeding[]
Parent with young chick
The Black-legged Kittiwake breeds in dense, numerous colonies of hundreds or even thousands of birds. It usually nests on inaccessible cliff ledges or in crevices, and more rarely on buildings close to the sea. A platform of moss and mud forms the base of the nest, a shallow cup lined with seaweed and dried plant material. The nests are often very close to each other. In May or June, the female lays 2 (sometimes 1 or 3) blue-grey or brown, 55 mm long eggs with grey and brown-red spotting, which both parents incubate for 25-32 days. Birds that live at higher latitudes lay larger eggs on average. The first chick to hatch may sometimes kill its siblings in order to have access to more food. The chicks are semi-precocial, but unlike Larus gull chicks, which frequently leave their nests and wander around, Kittiwake chicks sit still on their nests to avoid falling. Since they are at little risk of predation, they have no need for camouflage, instead being covered in silky, whitish down with shades of grey-brown. They are fed regurgitated food by both parents, fledging about 43 days from hatching.
Feeding[]
Compared to other gulls, which have a varied diet and frequently feed on land, the Kittiwake is highly specialized, feeding exclusively at sea. Unable to swim underwater, this bird feeds mostly on or just below the water surface. The diet of the breeding Kittiwake is made up mostly of small fish, generally under 10 cm long, such as sandeels, capelin and Arctic cod depending on geographical location. Other food sources include zooplankton, small crustaceans, offal, and occasionally worms, plant debris and insects. In winter, invertebrates such as squid and crustaceans make up most of the bird's diet. The Kittiwake preys on fish as they migrate towards the water surface to feed on floating phytoplankton. Since this migration occurs mainly at night, the Black-legged Kittiwake is very active at dawn and at dusk, and despite being a diurnal bird, it has been seen hunting at night by taking advantage of artificial light. It hunts mostly by plunge-diving, but also by plucking food items from the surface without landing or while swimming. It feeds almost exclusively at sea and rarely on the shore, and like many seabirds, is known to follow fishing vessels to take scraps. The Kittiwake occasionally steals food from other seabirds such as terns or auks.
Distribution and habitat[]
The Black-legged Kittiwake's preferred breeding grounds are rocky coasts and islands with steep cliffs. An oceanic species, this gull is mostly found in Arctic and sub-Arctic waters. R. t. tridactyla nests along the coasts of central-northern Canada, Greenland, Iceland, western and northern Europe and Arctic Russia up to the Severnaya Zemlya archipelago; during the non-reproductive period it wanders in the North Atlantic, generally remaining between the Tropic of Cancer and 60 ° north latitude, and between the Sargasso Sea and the coasts of West Africa. R. t. pollicaris nests along the coasts of north-eastern Siberia, Kamchatka, the Sea of Okhotsk, the Kuril Islands and throughout the Bering Sea up to continental Alaska; in the non-reproductive period it winters in the open sea, going south through the Japanese archipelago and east along the western coasts of Canada and the United States up to California.
Gallery[]
