Cormorants and Shags (Family Phalacrocoracidae)
David Thompson, Franz Smith, and Taoho Patuawa
General Description
Cormorants and shags represent a group of aquatic birds comprising the family Phalacrocoracidae, commonly characterised by a long, serpentine neck, elongate body form, and a strong, hooked bill. These birds are largely encountered in sheltered and coastal areas, but also inhabit estuarine and freshwater environments. Taxonomically, the IUCN now recognises a single genus, Phalacrocorax, within the family. Formerly, New Zealand species were included in the genera Stictocarbo and Leucocarbo.
Their plumage is permeable underwater, shedding air and reducing buoyancy, while out of water, plumage traps air and increases thermal insulation. This characteristic means that swimming in cold water is reduced to less than 30 min or birds can become hypothermic. The diet of cormorants and shags varies from fish to bottom feeding of invertebrates. As some of these species can also inhabit freshwater lakes, rivers, and streams, their diet can also consist of freshwater fishes, crustaceans, and molluscs. For some species, such as the Chatham Island shag, Phalacrocorax onslowi, the diet is poorly known.
Breeding is typically colonial, with individuals defending small nesting territories. Colonies are often densely packed and associated with other wading-bird species. Clutch sizes are typically two to four eggs, but range from one to seven eggs. Incubation lasts about a month in most species. After hatching, nestlings are cared for for approximately 50 days and are fed by both parents for two to three months after fledging. For most species, there is little information on the life-history characteristics, such as age at first maturity, and aspects of their population dynamics.
Flight and foraging for many species of shag and cormorants tend to be restricted to short geographic distances. For example, the Campbell Island shag, Phalacrocorax campbelli, is believed to range mainly within 10 km of the island and adjacent seas, while dispersal in the Stewart Island shag, P. chalconotus, is limited to within 15 km of land.
The global diversity of the family Phalacrocoracidae comprises 34 species, with 12 species breeding within New Zealand, 35% of the total. Of the 12 recognised species breeding in the New Zealand region, no fewer than 8 are endemic, representing about 67% of New Zealand's cormorant and shag fauna.
Status
Of the 12 shag taxa that breed within the New Zealand region, the Chatham Island shag is classified as "critically endangered" by the IUCN. The Pitt Island shag, Phalacrocorax featherstoni, is classified as "endangered", whereas the Campbell Island shag, the New Zealand king shag, P. carunculatus, the Stewart Island shag, the Auckland Island shag, P. colensoi, and the Bounty Island shag, P. ranfurlyi, are classified as "vulnerable" by the IUCN. All other New Zealand species are classified as "least concern" by the IUCN.
Key Locations
For most species present in New Zealand, breeding colonies are now restricted to predator-free islands and managed headlands on the mainland. The majority of species are isolated to offshore islands in the subantarctic. The Campbell Island shag is restricted to Campbell Island; the New Zealand king shag breeds only in the Marlborough Sounds and is largely confined to the Cook Strait region; the Stewart Island shag breeds only in southern New Zealand from Timaru to Foveaux Strait; the Auckland Island shag is restricted to the Auckland Islands; the Chatham Island and Pitt Island shags are restricted to the Chatham Islands; and the Bounty Island shag is restricted to the Bounty Islands.
The spotted shag, Phalacrocorax punctatus, breeds only in New Zealand, at sites in the Hauraki Gulf, Wellington Harbour, Nelson/Marlborough region, Banks Peninsula, Otago and Southland.
The black shag, Phalacrocorax carbo, and the little shag, P. melanoleucos, are both distributed widely throughout New Zealand. The little black shag, P. sulcirostris, breeds widely throughout the North Island, primarily in central North Island lakes, dispersing in autumn and winter to coastal bays and inlets; and the pied shag, P. varius, breeds in coastal areas of the North and South islands, and Stewart Island, including inshore islands and on freshwater lakes near the sea.
Summary of Threats
As some species nest on cliff and rocky terrain, there is little threat to nest damage, while other species are particularly vulnerable to this type of disturbance. Because of their low dispersal, established colonies are nevertheless likely to be drastically affected by any disturbance. As these species typically inhabit sheltered waters, such as harbours, inlets and sounds, they are also vulnerable to impacts from shipping activities and pollutants in harbours. Oil and petroleum spills represent a key threat in these areas.
In coastal foraging areas, cormorants and shags are also vulnerable to fishing activities, such as set nets, trawling and longlining. These birds are caught in fish and crayfish pots, and are also likely to interact with aquaculture farms, which can potentially serve as a threat through entanglement in gear.
Typical Habitats
Comorants and shags are generally found in near-shore coastal areas, estuaries, and riverbeds. Shags tend to nest on ledges and vertical cliffs, with some species nesting in trees. Several species are restricted to islands without introduced mammalian predators (eg, cats, rats).
State of Information
The population dynamics and diet of many of the species of cormorants and shags are poorly known, in particular, the island endemics of the subantarctic islands.
Significance for Maori
The general Maori term for the shags is kawau (or sometimes koau), however there are a number of specific names such as karuhiruhi (pied shag), kawau pu (black shag) and kawau paka (little shag). The strong-tasting adult kawau were rarely eaten, but there were instances when chicks were collected from nests to be used as a food source. The feathers were also rarely used on cloaks or as ornaments. Kawau were, however, a strong symbolic figure in the Maori world, and were often used metaphorically in stories or poems due to their determination and success as predators. This ability, matched with the ease in which they swallow their prey, made it appropriate to liken triumphant warriors to kawau. Kawau were also renowned for their strong and unswerving style of flying, and because of this, a long-distance traveller who would not be distracted from his purpose was likened to the bird.
Key References
Marchant, S and Higgins, P J. 1991. Handbook of Australian, New Zealand and Antarctic birds. Vol. 1: Part B. Ratites to Ducks. Oxford University Press. 1408pp.
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 5: Cormorants and Shags (Family Phalacrocoracidae) in New Zealand
| Taxon | Common name | Breeding Species | Endemic Species |
|---|---|---|---|
| Phalacrocorax campbelli | Campbell Island shag | 1 | 1 |
| Phalacrocorax carunculatus | New Zealand king shag | 1 | 1 |
| Phalacrocorax chalconotus | Stewart Island shag | 1 | 1 |
| Phalacrocorax colensoi | Auckland Island shag | 1 | 1 |
| Phalacrocorax onslowi | Chatham Island shag | 1 | 1 |
| Phalacrocorax ranfurlyi | Bounty Island shag | 1 | 1 |
| Phalacrocorax carbo | Black shag | 1 | 0 |
| Phalacrocorax melanoleucos | Little shag | 1 | 0 |
| Phalacrocorax sulcirostris | Little black shag | 1 | 0 |
| Phalacrocorax varius | Pied shag | 1 | 0 |
| Phalacrocorax featherstoni | Pitt Island shag | 1 | 1 |
| Phalacrocorax punctatus | Spotted Shag | 1 | 1 |
| Total | 12 | 8 |
Figure 22: Campbell Island shag Leucocarbo campbelli breeding.
Figure 23: Chatham Island shag Leucocarbo onslowi breeding.
Figure 24: New Zealand king shag Leucocarbo carunculatus breeding.