Banded dotterels are present on braided rivers during the breeding season in August-January, and usually, the most frequently encountered native bird species. They favour nesting in the more stable and low-stature vegetated areas along the outer margins of the main waterways (distribution map).
The double-banded plover (Charadrius bicinctus), known as the banded dotterel, double banded plover, or tuturiwhatu (Māori) in New Zealand, is a small (20cm) wader in the plover family of birds. It lives on beaches, mud flats, grasslands and bare ground. Two subspecies are recognised, the nominate Charadrius bicinctus bicinctus breeding in New Zealand and the Chatham Islands, and Charadrius bicinctus exilis breeding in the Auckland Islands.
Adults in breeding plumage are white with a dark greyish brown back, a distinctive brown breast, and a thinner band of black below the neck and between the eyes and beak. Younger birds have no bands and are often speckled brown on top, with less white parts.
They are fairly widespread in the south of New Zealand, but not often seen in the north. The nominate subspecies Charadrius bicinctus bicinctus is seen along mainland braided rivers, however it is also known to nest on gravel beaches.
It is partly migratory, breeding in New Zealand and the Chatham Islands and some wintering in Australia, New Caledonia, Vanuatu and Fiji, others staying in New Zealand. The Auckland Islands subspecies is sedentary but some birds move from their territories to the shore. Like all braided river bird species, numbers are declining.
Conservation projects on braided rivers are focussed on improving habitats by island formation, weed clearing, trapping pest mammals, and in some areas reducing the population of predatory black-blacked gulls, in order to protect colony nesting species: black-billed gulls and black-fronted terns. Efforts to conserve these two species have collateral benefits for less visible nesting species including banded dotterels.
Recent research (2021 and video an report below) indicates that the population may be declining faster than previously thought, however more data is needed.
Coastal gravel beaches like that at South Bay, Kaikaour (see videos) provide an abundance of open nesting habitat suitable for banded dotterels. In 2015, an ongoing research project was initiated to measure the breeding success of dotterels in this area, understand the factors leading to nest failure, and employ management strategies to improve nesting success.
Predation from hedgehogs and cats was soon identified, leading to the experimental use of ‘nesting exclosures’. This led to improved breeding success. However, the following year at least one cat identified the cages as a marker for a potential meal and waited for dotterels to leave the cage before killing them.
This kind of adaptive predatory behaviour is not uncommon. Harriers, for example, have been seen to use trail cameras as signposts for the location of nesting birds. This emphasises the need to measure the effectiveness of management strategies and adapt to predator behaviour accordingly.
The following season, in spite of the dotterels being a protected species, the local council declared the beach suitable for freedom camping. Breeding success that year plummeted.
The initial research proposal is here. The full background to the story of the South Bay dotterels was presented at the 2019 Braided Rivers Seminar and is available here. Note: this is a single document PDF: Section one: photos; section two: written outline.
Research & references
- 2021: O’Donnell; Distribution and long term population trends of banded dotterels on braided rivers in New Zealand Braided Rivers Seminar July 2021.
- Managing predation on ground-nesting birds: The effectiveness of nest exclosures (Biological Conservation 136)
- Nest Predation Management: Effects on Reproductive Success in Endangered Shorebirds (Journal of Wildlife Management 72)
- Piping Plovers nesting at Presqu’ile after a 100-year absence (Conservation group newsletter: Ontario, Canada)
- Cages and emetics rescue wading birds: Decoy eggs injected with a drug to induce vomiting in predators (Science News)
- Nests, Eggs & Chicks (Nebraska Environmental Trust)