Bar-tailed godwits can fly about 12,000 km at one time – further than any other known bird. This recent discovery excited ornithologists around the world. Dr Phil Battley from Massey University’s Ecology Group and PhD student Jesse Conklin have been tracking and researching godwits’ flights from New Zealand.
The flight path
The researchers found that godwits leave New Zealand from various estuaries (Manawatū, Miranda, Golden Bay, Christchurch, Otago and Southland) from the second week of March to the end of the month. It seems they fly direct from New Zealand to eastern Asian estuaries (Japan, Korea and China). The birds leave Asia for breeding grounds in Alaska in May. After breeding, they refuel on the coastlands of south-western Alaska (Yukon-Kuskokwim delta and Alaska Peninsula). They then return to New Zealand on a non-stop flight across the Pacific Ocean, taking 7–9 days, from September to mid-October.
Preparing for flight
To prepare for the flight, the godwits need fuel. The average godwit normally weighs about 300 grams. After fuelling for the trip, they weigh about 600 grams – doubling their weight in fat. Even their kidneys, liver and intestines shrink to make room for more fat (so they don’t exceed maximum weight for efficient flight). Their fuel (food) is predominantly marine polychaete worms, which they extract from muddy sediments using their long bills. They also eat small bivalves and crabs.
While in New Zealand, birds also replace their flight feathers, growing new ones so that they will be strong enough to last them 30,000 km flight.
You can tell if godwits are getting ready to take off on migration. They become more active than usual, walking around, fluffing their feathers, having a bath and calling to others with a very distinctive call – it’s as if they’re asking the others who else is coming on this trip. They leave in groups.
Godwits fly extraordinary distances yet they aren’t particularly different from other migrating birds. It’s just that they do everything really well. Structurally, they have a wing shape designed for fast, efficient long-distance flight. Their feathers are very sleek so that the wind can pass over as smoothly as possible.
The birds also counteract wind resistance (drag) by flying in flocks. The benefit of flying in a flock is that they fly in a V-formation. This means the bird at the front cuts into the wind first so that there is less wind resistance for the other birds. This makes flying easier for them, and as a result, the whole flock benefits by not becoming so exhausted. The birds have turns at taking the lead because the lead bird encounters the most drag and has to work the hardest.
Godwits fly at about 60 km/h, flapping their wings most of the way. They do not have completely waterproof feathers, so they can’t stop for a rest at sea. During the flight, they use up the fat they have stored plus some of their muscle tissue, which increases before the flight to cope with their extra weight. As they get lighter, the muscles do not need to work as hard and therefore don’t need to be as big.
In his PhD research, Jesse explored the relationship between when godwits leave New Zealand and when they return. It appears groups of godwits return to New Zealand in the same order as when they left.
Jesse discovered that migration timing is linked to the breeding grounds in Alaska. The birds seem to know exactly when to leave, and they leave at much the same time every year.
Alaska is frozen over for about 6 months of the year. As it thaws out, millions of birds come from all over the world to breed. Each latitude throughout Alaska starts summer at a different time. The southern parts thaw first followed by the more northern parts. It appears godwits always go to the same breeding grounds.
The godwits that leave New Zealand in early March breed in the south, where the ice melts first, and birds that leave at the end of March breed in the north, where the ice melts last.
Nature of science
Sometimes it’s hard to get funding for science projects that don’t seem to have a benefit for people. Funding that enabled the discovery of godwits’ flight distances was initially granted because of a concern that godwits may spread bird flu around the world. Without this link to a benefit for people, the research may never have happened.
Every spring, bar-tailed godwits make the 11,000 kilometre journey from Alaska to New Zealand. Phil Battley talks birds and migration.