- The black shag is New Zealand’s biggest shag at over 2 kg and 88 cm in length. It breeds throughout New Zealand (inland and coastal) and is found in most parts of the world.
- The little black shag is less than half the size of its larger relative, and lacks a white face, being almost wholly glossy black. It is found throughout Australasia. In New Zealand it is largely restricted to the North Island and the top of the South Island. It is also found well inland.
- The pied shag is a similar size to the black shag, but the underparts of the body are white. It is also found in Australia. It has a patchy, coastal distribution in New Zealand
- The population of black shag has been estimated at 5,000-10,000 mature individuals, however, actual numbers are poorly known.
- The little black shag is thought to be relatively new arrival in New Zealand, and its distribution is still increasing. It may number several thousands.
- Pied shag have been fully surveyed in Wellington and the Marlborough Sounds, but not elsewhere. The population was estimated at 1,000-5,000 birds in 2012, but is poorly known.
- Pied shag is considered to be in decline, unlike the other two species. The reason for this decline is not well understood.
- All three species may be vulnerable to fishing activities such as craypotting, set-netting and inshore longline fisheries. Shag species have been shot in the past for perceived competition with recreational fisheries. This evidently still occurs occasionally.
- Evidence for the effects of introduced predators on New Zealand’s shag species is extremely limited. Few species have been particularly well-studied, including black, little black and pied shag. Pairs and colonies that nest on the ground rather than trees may be significantly more at risk.
Association with Plantations
- Wetland birds are found in and adjacent to many plantation forests.
- Wetland birds may be hard to detect due to their elusive behaviour.
- Habitat loss and degradation from wetland drainage, loss of riparian margins, and the effects of surrounding landuse.
- Invasion of exotic plants, which can seriously modify wetlands and reduce suitability for birds.
- Disturbance and motor wash from recreational boats
- High predation rates, particularly of pateke, mainly from dogs, cats and mustelids.
- Mammalian predation may also affect some other wetland bird species, but the extent of the impacts is unknown.
Management Options and Methods
- Habitat protection:
- Protect important wetland habitats and riparian buffers.
- Avoid using herbicides or pesticides close to wetlands.
- Ensure weeds are not inadvertently introduced to wetlands, e.g. via machinery or boats.
- Consider control options for existing, invasive, wetland weeds.
- Consider a staged removal of willows to ensure ongoing cover for crakes and ducks.
- Forest operations:
- Minimise damage to riparian and wetland habitat during road construction and harvest operations.
- Avoid grazing wetlands and their margins. Fencing may be appropriate in some situations.
- Avoid diverting run-off into wetlands.
- Minimise disturbance during spring breeding.
- If pateke are present, discuss predator control with neighbours and DOC.
- Injured or dead wetland birds (particularly the more threatened species, i.e. white heron, bittern and pateke):
- Place injured birds in a cardboard box (keep shaded) and deliver to a local vet, SPCA, DOC.
- Call DOC if bird is dead.
- Increase staff and contractor knowledge about wetland birds.
- For important wetlands that are likely to have the more threatened species, consider undertaking a bird monitoring programme:
- Counts of pateke flock sites in late summer.
- Fernbirds, spotless crakes and to a lesser extent marsh crakes and banded rails respond to taped playback calls.
- The booming calls of bittern are characteristic at dusk in September-October particularly during bright moonlight.
- Maintain a database of sightings.
Further Information and Support
- New Zealand Birds Online: black shag, pied shag, little black shag.
- Wetland Restoration: A Handbook for New Zealand Freshwater Systems. Landcare Research - Manaaki Whenua.
- Pest management - Department of Conservation, Regional Councils.