Nature / From Alaska to Christchurch, the flight of the bar-tailed godwit
Few birds have garnered such a loyal local following as Canterbury’s beloved bar-tailed godwit population.
Each summer more than 90,000 bar-tailed godwits make the longest continuous flight of any non-seabird from their breeding grounds in Alaska 12,000 kilometres away to estuaries across New Zealand.
It’s a journey that has captured the hearts of New Zealanders for decades, and nowhere is it more evident than in Christchurch, where a small number make the AvonHeathcote Ihutai Estuary their summer home. Before it was destroyed by earthquakes the Christ Church Cathedral bells rang out each September to mark their arrival, and for the past two decades, hundreds of people have ventured to Southshore Spit every autumn to bid them farewell.
Christchurch City Council ornithologist Andrew Crossland has been monitoring Christchurch’s bar-tailed godwit population since the mid-1980s. Growing up in Linwood, the estuary was his playground. He was just 14 years old when he first started doing bird surveys. Since then he has racked up more than 20,000 pages of field notes. ‘I wanted to know what everything was,’ he says. Andrew joined the Christchurch City Council’s Parks Team in 2002. He has worked tirelessly to help improve the outcomes for local birds by protecting and enhancing existing habitats and establishing new ones. Christchurch is a wonderful place for bird-watching, says Andrew. During the summer the estuary is home to more than 30,000 birds from 147 different species, while across wider Christchurch (including Banks Peninsula and Lake Ellesmere), 242 species have been recorded.
Located on the city’s back door, the Avon-Heathcote Ihutai Estuary is one of the few places where residents and visitors alike can enjoy many remarkable birds. However, it’s the bar-tailed godwit, the bird whose stylised form once graced the tail of the National Airways Corporation planes, the forerunner to Air New Zealand, that continues to enthral Cantabrians as it did Māori for hundreds of years. According to legend, the bar-tailed godwit (or kūaka) gave the first voyagers from Polynesia to Aotearoa the idea that there was something down south worth travelling for, as they watched it year after year hurtling past.
Thankfully much is known about the bar-tailed godwit today. A huge banding project worldwide 10 years ago means the life histories of many of these birds are pretty well-known, and the estuary’s proximity to Christchurch and the bird’s habitual tolerance of people makes constant monitoring easier, explains Andrew.
Bar-tailed godwits can live for about 20 years. The females are larger and have longer beaks. They like to eat sea worms, which are abundant in the estuary, and anything big and brown that moves like a skua or bird of prey makes them nervous. Born in the arctic tundra of Alaska and Siberia, where the food supply is plentiful and there’s 18-hour or 24hour daylight, young chicks can walk about, swim and feed themselves from birth, but stay close to the adults until they fledge the nest at about four to five weeks. Then as soon as the snow comes, it’s time for the adults to migrate southwards.
Andrew says ornithologists had long known the bar-tailed godwit covered an enormous distance flying from Alaska to New Zealand. But it was only recently that transmitters attached to birds confirmed that they fly non-stop (not even gliding, or stopping to eat) for six to eight days, averaging around 80 km per hour to reach their summer feeding grounds. Notably, they leave their young behind, leaving the young bar-tailed godwits barely a month old to fly from Alaska to New Zealand solo.
The bar-tailed godwits start arriving at the estuary in dribs and drabs from September to November. They spend the next few months doubling their weight and growing their breeding plumage, ready for the exhausting return flight home to breed, which includes a Yellow Sea stopover on the China-North Korea border. From there, it’s a short flight across the North Pacific to Alaska. Once back in the Arctic the bar-tailed godwits quickly find a mate and begin breeding. With almost 24 hours of daylight for much of the breeding season, they can pack a lot of living into a short window of time.
Nests are constructed on the ground. Three to four eggs are laid and are incubated by both parents until hatching at three weeks.
Each spring, Andrew eagerly awaits the bar-tailed godwits’ arrival; it’s a huge relief when the first birds touch down. This year Andrew spotted the first 38 of the migratory birds on Southshore Spit on 20 September. By 7 October, this figure had increased to 951, but he expected more birds to arrive over the coming weeks. With all the constant moving about and mingling one might ask how he can count how many are there. ‘Simple,’ says Andrew. ‘I count the legs and divide by two!’
In a poor year, bar-tailed godwit numbers at Southshore Spit have dwindled to as low as 1300, rising to 2200 in a good year. On average the summer population is around 2000. The new arrivals can be distinguished from those that have spent the winter in Christchurch by remnant red feathering in their tattered plumage, thin bodies, droopy wings and frantic feeding behaviour.
While the numbers seem stable, Andrew says there is rising international concern about the loss of their migratory refuelling spots on the China and South Korean coast, due largely to the drainage and landfill of estuaries and mud flats for industrial and economic development, and on the North Korean coast for obvious reasons. Worldwide the population was declining at a rate of 2 per cent annually, despite the great job being done locally to protect them. ‘If the food source dries up, they are in big trouble. They are sitting on a knife-edge.’
The Avon-Heathcote Ihutai Estuary received international recognition last year, becoming part of the East Asian-Australasian Flyway network of wetland areas along the route of migrating water bird. It joined the Firth of Thames, Farewell Spit and Awarua Bay Estuary in Southland as the only other New Zealand areas in the partnership, and the only urban wetland in Australasia to be included. The flyway network, which started in 2006, involves more than 130 wetlands from 20 countries used by migratory birds on their way to or from the Arctic. And recently the South Brighton Residents’ Association unveiled an $ 89,100 sculpture that they hope will continue to raise public awareness for the bar-tailed godwit and the importance of the estuary as a feeding ground for both it and many bird species. Designed by Bon Suter, it features seven painted, stainless steel bar-tailed godwits on top of tall poles, which allows them to rotate in the wind.
The new arrivals can be distinguished from those that have spent the winter in Christchurch by remnant red feathering in their tattered plumage, thin bodies, droopy wings and frantic feeding behaviour.