Bar-tailed godwits at Ahuriri Estuary

Image: Natalia Volna | Creative Commons

Introduction

A guide to birds you might see in the Ahuriri Estuary in Napier.

With the range of environments it offers to endemic, native and migratory birdspecies, the Ahuriri Estuary is one of the most significant habitats of its type on the east coast of the North Island.

Of the original 3,840 ha of Te Whanganui-ā-Orotu (the inner harbour estuary) existing prior to the 1931 Napier earthquake, only 470 ha remain. This protected area, the Ahuriri Estuary (which includes the Westshore Wildlife Reserve, Southern Marsh and the North Pond), has a range of habitats important to birds, fish, invertebrates and plant life. It is therefore crucial the estuary remains undisturbed.

Over 70 resident and migratory bird species feed and rest here. Many birds arrive each year from their arctic breeding grounds to recover and rebuild body condition and energy levels, before returning for the next round ofnesting and chick raising. Others gather here over winter to take advantage of the estuary’s abundant food supplies.

New Zealand resident waterbirds

Pied stilt (poaka)

  • Found in a variety of habitats from coastal mudflats and estuaries to lakes, riverbeds, swamplands and wet paddocks.
  • Nest on shingle riverbeds, sand dunes and pastures, and in the South Island and southern North Island move to coastal places from December to February.
  • Coastal and North Island breeders are non-migratory.
  • The estuary’s population is in the hundreds.

New Zealand shoveler (kuruwhengi)

  • Prefer fertile, shallow wetlands.
  • Typically feed in shallow water by dabbling and upending, so it is known as a dabbling duck.
  • Its spoon-shaped bill is adapted to sieving out seeds and small aquatic animals from the muddy sediments of shallow estuarine and freshwater habitats.

Black shag (kawau)

  • Breeding season is variable and may be delayed by duck shooting.
  • Feed on small and medium-sized fish.

Australasian bittern (matuku)

  • Live in tall, dense beds of raupo and reeds in freshwater wetlands. They also like damp pasture infested with tall clumps of rush or tall grass.
  • Numbers have declined due to the drainage and reclamation of wetlands, and cattle grazing in swamps, which damages breeding cover.
  • It is estimated that their population is currently between 250 and 1000 mature birds. An exact figure is difficult to ascertain due to their solitary nature and ability to blend into their environment, which also means they are rarely seen.

Other species commonly seen include pukeko, spur-winged plover, mallard, white-faced heron, black-backed gull, banded dotterel and Caspian tern.

Northern hemisphere migrants

Bar-tailed godwit (kuaka)

  • Breed from Northern Scandinavia across Northern Siberia to Alaska.
  • Make the longest known non-stop flight of any bird. The journey is 11000–12000 km undertaken in 8–9 days along a route from Alaska to New Zealand.
  • When it is time to migrate south, they wait for storms that provide tailwinds of 40–80 kph for the first 1500–2000 km.
  • Within hours of reaching New Zealand they begin feeding to replenish what they lost en route—about half their body weight.
  • Arriving from late September during the southern hemisphere spring, the majority of the 80,000–100,000 godwits head for Kaipara and Manukau harbours, the Firth of Thames, Farewell Spit, and the Avon–Heathcote estuary near Christchurch. In large flocks they feed on molluscs, crabs, marine worms and aquatic insects, probing the mud with their long bills as the tide recedes.
  • Four months after arriving in New Zealand, in preparation for the northward return flight, they start to stock up on food, doubling their body mass.
  • The return to Alaska is taken in two stages from March so they arrive in good condition to breed in May.

Golden plover

  • Breed on the arctic and subarctic tundra of Siberia and western Alaska.
  • Migrate south, arriving as early as September, but most arrive from October to early
    November. Depart northwards late March to early April.
  • In New Zealand (unlike in the Pacific Islands) they are notably alert and wary.
  • Feed in grassland, saltmarsh and the upper levels of tidal flats.

Knot (huahou)

  • Breed in Siberia and spend their winter in temperate and tropical estuaries of both hemispheres.
  • Reach New Zealand September to October, and return to the north March to April.
  • Feed mainly on small molluscs, as well as cockles and gastropods such as whelks.
  • Feed close to the tideline on intertidal mudflats and sandflats, often with godwits.
  • Exhibit a ‘sewing machine’ action when feeding, rapidly drilling the soft mud or wet sand with their beaks.

Other species sometimes seen include ruddy turnstone, far eastern curlew, American and Asian whimbrel, Siberian tattler and red-necked stint.

New Zealand migratory waterbirds

White-fronted tern (tara)

  • Migrate in autumn—large numbers of young birds and some adults to the southeast coast of Australia. Many adults remain on New Zealand coasts throughout winter.
  • Breed in large colonies, which only last a short time, on sandy beaches, low-lying sandspits, shingle or shellbanks and rocky islets.
  • Roost in flocks of up to 2000 at estuary mouths, and on beaches and shellbanks.
  • Feed on small surface-shoaling fish such as smelt and pilchards.
  • In Hawke’s Bay they breed irregularly on the spit at Waitangi Estuary and Cape Kidnappers so can also be considered a resident species.

Wrybill (ngutuparore)

  • Only found in New Zealand.
  • Breed in Canterbury and parts of inland Otago on braided rivers.
  • After breeding, most fly north to large tidal harbours.
  • Their main northward movement is in the last couple of weeks of December and early January. Their return from northern mudflats starts in early August and peaks mid-month. 5–10 percent stay in the north throughout the summer.
  • Commonly seen feeding on tidal flats or resting on high-tide roosting sites in the estuary.
  • Feed on invertebrates found under rocks in rivers and on small crustaceans in tidal mudflats (they prefer silty mud).

Royal spoonbill (Kotuku-ngutupapa)

  • Have been coming to New Zealand for more than a century but only started breeding here in 1949. Breed mostly in the South Island and disperse in autumn to their wintering sites.
  • Have increased from 52 birds in 1977 to 610 in 1995. 102 were seen at Ahuriri in 2009.
  • Feed mainly on small invertebrates, fish and frogs in tidal mudflats. Feed by touch both at night and during the day.
  • Very gregarious and always seen flying, feeding and roosting in flocks. Can be seen on all areas of the estuary and surrounding wetlands.

Other species seen include black-fronted dotterels, white heron and torea.

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