Status and numbers
This is an endemic species, meaning it is found only in New Zealand. There are two distinct subspecies, with ranges that are widely separated geographically. The southern subspecies (C. o. bscures) was once widespread in the South Island, but currently only breeds on exposed hilltops on Stewart Island. In 1992, this population had fallen to 62 individuals, but as a result of management it now numbers 250-300 birds. Southern New Zealand dotterels are larger and darker than the northern subspecies. Because of its very small population, this subspecies has a threat ranking of Nationally Critical, the highest possible under the New Zealand ranking scheme.
The northern subspecies (C. o. aquilonius) is thinly spread around the coast of the North Island. At the last complete census in 2007, there were about 2200 individuals. The northern New Zealand dotterel is ranked Threatened (Nationally Vulnerable) and is considered Conservation Dependent, meaning that without management its threat status is likely to deteriorate.
The northern New Zealand dotterel is almost entirely coastal and typically breeds on sandy beaches, sand spits and shell banks. In urban areas it also nests on grassed areas or bare earth a short distance inland, including on building sites, quarries, golf courses, motorway verges, and airport margins.
The bulk of the population is now found on the east coast, mainly in Northland, Auckland, Coromandel, and Bay of Plenty; between them, these areas currently hold more than 80% of the population. This range is expanding slowly southwards, with a few pairs now breeding in and south of Hawke’s Bay. On the west coast of Northland and Waikato however, numbers are declining.
Although early nests are sometimes found in August, most pairs do not start breeding until September or early October. Three eggs are laid, normally in a simple scrape in the sand, and are normally incubated for 28-30 days. The chicks are mobile soon after hatching. They are protected by their parents, but find all their own food. They can normally fly after about 5-7 weeks. Once they leave their natal site, juvenile dotterels wander the coastline for a year or more, before settling down to breed, normally at the age of two. A few return to their natal site to breed, but most breed elsewhere.
The core period for breeding is between September and January, after which most birds gather at traditional post-breeding flock sites (usually at nearby tidal estuaries) for several months. From late May or June onwards, pairs begin to return to their breeding sites.
Threats and conservation
Predation (mainly of eggs and chicks) is the major threat. Important mammalian predators include stoats, cats, and hedgehogs. Harriers, black-backed gulls, and red-billed gulls also cause losses. Breeding success is also reduced by flooding and crushing of nests, and disturbance during breeding caused by recreational use of beaches by people, vehicles and dogs. There is ongoing loss or degradation of breeding habitat by coastal development, particularly on the North Island east coast.
Management of northern New Zealand dotterels began in the late 1980s, and in 1993 the first recovery plan was published. At unmanaged sites, breeding success is normally low. Management to improve breeding success includes effective control of mammalian predators, control of avian predators if necessary, fencing of nesting areas, reduction of disturbance, reduction of nest loss to flooding and crushing, and advocacy to increase public awareness of the species and its problems.
Importance of Omaha to the species
The dotterel population at Omaha has been monitored and studied for 25 years. As a result, we know that Omaha Spit is a site of international importance for northern New Zealand dotterels. It is an important breeding site, and also holds one of the largest post-breeding flocks. Over the past 25 years, the number of pairs breeding on the spit has increased from 4 or 5 to 15-16 currently. At the same time, the autumn flock has increased from about 45 birds to more than 100, making this the third-largest flock known.
Banding has shown that birds at the Omaha flock breed mainly at Pakiri River, Tawharanui, and Omaha itself, with smaller numbers from the Mahurangi coastline, Beehive Island and Motuora Island.