Spotted Shag

Identificazione

The spotted shag is a medium-sized marine bird. They are usually between 64 and 74 centimetres (25 and 29 in) high and weigh between 700 and 1,200 grams (25 and 42 oz). Their bodies are very slim and they have a very distinctive black, decurved, double crest growing on their nape and their forehead. They have a long, slender, orange-brown coloured, hooked bill and yellow-orange feet. The feathers on their bodies are grey and blue. The adults have small black spots on their backs and wings, which gave them their name. Their irises are brown, while the ring around the iris is blue. They have a small patch of bare facial skin between their eyes and bill, which turns green-blue just before breeding season. Furthermore, non-breeding adults do not have crests and have paler underparts. The males and females do look very alike, there is almost no sexual dimorphism. Sexual dimorphism means that the males and females of a species look different and can be easily told apart, which is not the case for the spotted shag. However, the males and females can be told apart by their calls and mating behavior. Normally they do not produce much noise, only when they are at resting, roosting and nesting areas. When they produce sounds, it can be heard as loud grunts. Spotted shags usually fly in V-formation and it is hard to tell males and female apart. In flight, they look slender and pale, while their rump and tail look darker.It is hard to estimate the total number of spotted shags in New Zealand; estimates are between 10,000 and 50,000 breeding pairs (20,000 to 100,000 birds). In the past, the number of spotted shags has been limited by the availability of food, which caused an increase in number during the late 1980s.

Tassonomia

The spotted shag was initially called the ‘crested shag’ by Johann Forster. He shot the bird while out hunting with the famous James Cook. Swedish naturalist Anders Sparrman was Forster's assistant on this second voyage of James Cook, and he described the spotted shag in 1786 as Pelicanus punctatus. Bonaparte erected the separate genus Stictocarbo for it in 1855. It was later returned to its original genus.<p>In 1930, the Stewart Island population was described as a separate species, the blue shag (Stictocarbo steadi), distinguished by its narrow rather than broad white stripe on its head and neck.<p>A 2014 molecular study by Kennedy and Spencer found that the spotted shag belongs to a clade of Old World cormorants. Its closest relative is the Pitt shag (P. featherstoni), and their common ancestor split from a lineage giving rise to the black-faced, pied and little black cormorants of Australia.

Nome scientifico

Phalacrocorax punctatus

Autorità

(Sparrman, 1786)

Ordine

Suliformi

Famiglia

Phalacrocoracidae

Genere

Phalacrocorax

Areale e habitat

The spotted shag is endemic to New Zealand. It breeds only on the coastlines of New Zealand and some of the offshore islands, being mainly found on the South Island. High numbers can be found on the west coast and near Stewart Island, but they also inhabit some places on the North Island. During breeding, they can mostly be found on their breeding sites, but otherwise they are more dispersed to other coastal areas. Large colonies can be found around Banks Peninsula near Christchurch, and in a rocky outcrop named the 'Shag Rock' in Wellington Harbour. Phalacrocorax punctatus are locally common, with estimates of numbers nationwide varying from 10,000 to 50,000 pairs.<p>This species prefers to nest on cliffs along rocky coasts where they occupy ledges or cracks, forming colonies of over a thousand birds. They seldom go into freshwater environments or enclosed estuaries (Heather &amp; Robertson, 2000). Seaweed is often used in lining the nests, the foundation of which is made of sticks.

Migrazione

Specie stanziale

Comportamento

Comportamento migratorio: Specie stanziale.

Conservazione

La specie non è considerata minacciata. Tuttavia, sebbene un tempo fosse molto diffusa nel golfo di Hauraki, le sue popolazioni hanno subito un forte declino nel corso dell'ultimo secolo. Analisi recenti del DNA hanno indicato che gli uccelli originari delle regioni settentrionali della Nuova Zelanda sono geneticamente distinti, aumentando la preoccupazione per il continuo calo della specie ad Auckland e nelle aree circostanti.

Tendenza della popolazione

unknown