The Seasons in the Tauranga lives of New Zealand’s migratory birds
by Paul Cuming
Autumn Is the time the maximum numbers of birds are here in the Bay, with numbers of NZ breeding shorebirds and arctic migrants, or waders, numbering in their 1000s. 100s of Banded dotterel, Pied Stilt, South Island Pied Oystercatchers (SIPO), and up to 100 Wrybill make up our main local flocks, while Godwits, Knots and Turnstone make up our visitors.
Summer breeding birds such as Wrybill are here from their breeding grounds, the braided rivers of the South Island, and SIPO from mountaintops such as the Old Man Range in Central Otago. Banded dotterels come from many different areas such as the rivers of Canterbury, the Lakes of Rotorua and the deserts of the Volcanic Plateau.
March to May is the time when the great migration North to Alaska and Siberia starts, and at the end of the season, about 10% of the arctic migrants remain, mostly first year birds. Knots seem to like Tauranga Harbour as they seem to assemble here in large numbers before departure – (600 sometimes seen) Godwits and turnstones & knots make stopovers at various locations on the way back North, like the Gulf of Carpentaria, Vietnam, Korea and China. Some go through the Philippines and Indonesia. 8 godwits which were tagged in NZ were seen in China in 2004, just one example of how we know these routes. This journey represents over 10,000km. This is enough to depreciate the car you just bought new by a sizeable chunk of money, for comparison, and these birds do it every year.
Kingfishers appear more frequently down here as well, looking for the crabs that will sustain their diets, after the cicadas have finished. Some SIPO start their migration South in July.
The inland parts of the South Island are their main destinations, getting their nesting done and out of the way during the September-November period before the summer droughts that often affect the areas arrive and dry out the wet patches they feed around.
Spring is the opposite of Autumn with the local Wrybill, the rest of the SIPO, and Banded dotterels exiting stage left, and the Pied Stilts leaving the Bay almost altogether. The reason for this is the decreased amount of wet patches on farms that have now been either converted to horticulture or dried out.
Over 30,000 arctic waders attempt the 12,393km journey to New Zealand from Siberia and Alaska in our Spring, some leaving their chicks after only a few weeks. These chicks follow their parents 8-12 weeks later, without any guidance. The Arctic waders however, have some tricks up their feathered sleeves. First of all, the Knots arrive from Siberia with only two stops. This process takes less than 2 months.
But the star is the Godwit, which makes the journey from Alaska to New Zealand without stopping, taking a few weeks to catch a favourable wind. It takes on so much fat, 55% of its bodyweight, then reduces its digestive organs at the last moment with the aim of reducing ballast. U.S. Geological Survey scientists recently discovered that the plump birds can actually reduce the size and weight of their muscles and organs by up to 20 percent before takeoff. After landing in NZ , the burned-out birds begin a body-building regimen and break their two week fast to regain their muscle and organ weight. And we complain about a little jet lag. Birds flagged in Alaska prior to migration have been seen in New Zealand such a short time later as to make it mathematically impossible for that bird to have stopped anywhere on the way. In the immortal words of the Miranda Shorebird Centre manager Keith Woodley, “we have to assume they know what they are doing”
The most common gulls are the Red-billed Gull, and the Black-backed Gull. Matakana Island has Black-backed gulls nesting, to the annoyance of the NZ Dotterel.
NZ Dotterels flock post-breeding, and a count recently put the Bay at 145 birds. This is up from 110 in 1996, but not as high as DoC would have liked, given the success of the Matakana predator control programme.
White-fronted terns have nested at Coronation wharf and the old Turret Toad bridge pilings, with some success at the former site. It just goes to show that there are limited sites which the terns have to choose from for them to use such public places to nest.
Caspian terns have nested on Matakana but I haven’t heard how they’ve got on this Summer. Pied Shags have successfully raised chicks on the Mauao roost site, with four nests counted in the Summer. Lack of large bodies of fresh water in the Tauranga area mean Little and Black Shags breed mainly outside the region, even some on Mayor Island where there are large crater lakes.
So we are back to where we were when we started, in Autumn.
I’ll just finish with another startling fact: By its 13th birthday, the Knot would have flown a distance equal to the moon…and back