A season on the river
The notorious Canterbury nor’ wester burns across the landscape sucking oxygen and moisture out of the air with equal ferocity. The stones of the Waimakariri riverbed warp and shiver in the reflected heat; mirages dance ephemerally in the air.
A rhythmic, breathy sound comes to me across the stones, as if some great beast lies nearby, gasping in the heat of the day. But this is not one beast . . . it is hundreds. Some 300 tarapuka in their riverbed colony, each black-billed gull standing over its nest, all panting in unison, holding steadfast in the sun to give their chicks a slim patch of shade. It is late November, the middle of the river season.
It was cooler when, on the Ashley-Rakahuri estuary, the arrival of the ngutuparore toward the end of August signalled the beginning of the river season. At first in twos and threes and then in dozens the wrybills turned up at the estuary after their long flight from over-wintering grounds far to the north. Hungry, and with breeding to build condition for, they fed in the tidal mud with the voraciousness of shrews. By October, all had moved inland to braided rivers where they could find the clean, weed-free, banks of river stones among which they build their shallow nests. A few pair simply head upstream on the Ashley-Rakahuri but others go further afield to Canterbury’s bigger braided rivers: the Waimakariri, Rangitata, Rakaia, and beyond.
Pohowera numbers also swell in August. Many of these hardy dotterels spend their whole lives on the coast, but those that breed inland on the braided rivers tend to migrate west to Australia. Splendid in their fresh breeding colours of red and black bands, they return in early spring to join the over-wintering locals to feed up, find mates and establish nesting territories. For much of the year, banded dotterels can be cautious birds, wary of too close an approach, but with spring comes hormone-fuelled courage. The males hotly contest for territory and established pairs are remarkably bold, especially once they have a nest to defend and will tolerate a patient photographer within two metres.
On the Ashley-Rakahuri estuary, flocks of tarapiroe (black fronted tern) have wintered over, along with their cousins the tara (white-fronted tern), taranui (Caspian tern) and the black-billed gulls. But as spring progresses these strikingly beautiful terns – capped in black velvet with road-code orange bills and legs – also head inland to share the clean river shingle with the wrybills, dotterels, black-billed gulls and the other braided river nesters. Some of their white-fronted cousins also choose to move inland, choosing higher shingle banks in the river, often near the added security of other bird colonies.
Some of the black-fronted tern nest in sizeable colonies alongside the black-billed gulls, which is a great strategy because the gulls are alert and ferocious sentries. But others scatter themselves along the Ashley-Rakahuri in small groupings of nests, wherever the shingle banks provide the right conditions.
There they are joined by the poaka (pied stilt), spur-winged plover, torea (South Island Pied Oystercatcher), and the karoro (Southern black-backed gull).
By mid November there are many voices on the river as the river nesters begin to hatch their young and attend to the task of feeding and raising their chicks.
Each has a different style.
The black-fronted tern do little more than scrape a hollow in the stones, perhaps adding a few rudimentary twigs or scraps of weed, but essentially their eggs lie directly on the stones. The stilts and oystercatchers use a similar tactic, with little if any covering over the stones to cushion the eggs.
Wrybills seem to be just as perfunctory in the nesting department, but a closer look reveals something remarkable – the tiny bowl they have made among the stones has been lined with very small pebbles . . . an exercise in remarkable patience and care!
The gulls, on the other hand, build actual nests. The black-billed nest is fairly basic but provides a platform of twigs and river detritus to give their eggs some cushioning. Their large cousins, the black-backed gulls, build substantial piles of tangled sticks and river weeds that seem unnecessarily large for the modest eggs cupped within, but this commodious affair is revealed as practical when the fast-growing chicks soon fill it to its borders.
The waders all have chicks that pretty much feed themselves from the moment of hatching, relying on their parents for protection and the lessons of life, but quickly learning to find for themselves the bugs and grubs in the river shallows. The terns and gulls are more solicitous, bringing food to the nests to feed the demanding chicks. Even when fully fledged, young tarapiroe will sit on the ground begging food from their parents. In tern colonies an overhead adult carrying a fish sets off a chorus of excited calling as each chick hopes it is their parent that has returned.
The gull chicks grow quickly and frequently form crèches in between their parents’ visits with food; bundles of down moving together around the colony and down to the river’s edge to bathe, swim and exercise their wings.
Wrybill, stilt, dotterel and plover chicks stick close to their parents, freezing to invisibility among the stones when a parent bird calls a sharp alarm. In the mixed colonies the alarm call of a stilt will have the same impact on the chicks of other species as it does on its own youngster, with all of the chicks hunkering down. This is an excellent tactic for aerial predators such as the kahu (Australasian swamp harrier) or the karoro glide on by, but is of little use against the introduced mammalian predators such as stoats and feral cats, which can hunt by smell as well as sight.
Late summer finds chicks fledging all over the place and testing their hunting skills. Tarapiroe glide up and down the river, imitating their parents with quick dives from a near hovering flight to seize fish. At first they are clumsy and miss more often than not, but patience and repeated tries are finally rewarded.
By early autumn all of the birds that have managed to keep their young alive throughout the season, surviving unexpected floods and predatory attacks from natural and introduced predators alike – let alone disturbance by careless humans and their recreational vehicles – begin to depart; some in the company of their newly fledged teenagers, but others leave the ‘kids’ behind to fend for themselves before they, too, driven by instinct, gather together to flock to their wintering-over grounds on the coast, further north or across the Tasman sea.
The estuary becomes busy again now as the river breeders return to fatten up. Many, such as the black-fronted terns and the black-billed gulls, will stay, utilising the riches of the coastal waters to see them through the winter ahead. The wrybill all fly up north where they flock in their thousands along the coast of the Firth of Thames and in other northern estuarine areas. Some banded dotterel stay in their home territories on the coast, but those that have bred inland will return to the coast and many travel to Tasmania and southeast mainland Australia in an unusual east-west migration.
Stilts and plovers, too, have a mixed response to the approach of winter. Some stay put, others move to the coast, and still others make long flights to preferred over-wintering territories elsewhere in the country.
The river is not entirely abandoned though. Many stilts, dotterels and plovers remain, as do some of the gulls, and winter visitors also move in, including the kotuku that have left their breeding colony on the West Coast to scatter throughout the country in lakes, rivers and estuaries.
Soon, the perils of winter floods and frosts will pass, and spring will come around again. And then, just as the whitebait begin to come in from the sea, the river breeding specialists will return to trust their eggs to the stones and gamble again with the fickle floods of spring.
(All photos in this blog copyright Steve Attwood/Auldwood Photography. Permission must be sought for use, reproduction or copying in any form)