Well recall my first encounter with the southern crested grebe. It was at the end of a warm spring day in the mountains, with the retreating snow looking like streaks of ice cream splattered on the ranges. My daughter and I had stopped at Lake Georgina, south of Craigieburn Range, to have something to eat and drink before returning home to Christchurch. As we sat quietly in the evening stillness, two duck-sized birds swam past us, their paired wakes breaking the glassy reflections of the tussocked hills which hem in the small lake.
Their long white necks, distinctive ruff of chestnut with black edges about the neck, and black double crest on the top of their heads made them unlike any other bird we had seen. Once home we searched through our book of New Zealand birds and located only a single candidate: the southern (or Australasian) crested grebe, Podiceps cristatus australis, a subspecies of the great crested grebe found in Europe, Africa and Asia.
When we discovered there was an estimated total population of less than 250, scattered over Fiordland, Westland, and Canterbury, we expected that would be our once-in-a-lifetime sighting. However, since that brief encounter years ago, we have seen them in many places, from Lake Benmore in the south to Lake Grasmere, near Arthurs Pass, in the north, frequently in pairs during the breeding season. We make a special point of looking for them when we are in the mountains, and rarely have we been disappointed, seeing up to 10 in a day when we’ve been out grebe-spotting.
It is a matter of some dispute as to who first correctly identified the southern crested grebe in New Zealand.
The earliest clear identification was by the naturalist T. H. Potts, in April 1856, at Lake Selfe, in the Coleridge area—a lake which still has a significant grebe population. Prior to that date, Charles Heaphy had mentioned the presence of “divers” (a name which fits the grebe’s feeding habits) on Lake Rotoroa in 1846, but he used the same term to describe a type of river bird in 1842. George Grey presented a number of bird skins to the British Museum in 1847, among which was a southern crested grebe, and Julius Haast correctly identified
the crested grebe in 1860 on a visit to Lakes Rotoiti and Rotoroa.
Although early observers noted breeding populations of grebes as far north as Lake Waikareiti, in what is now Urewera National Park, the bird has never been common in the North Island, primarily because of the lack of clear, high-country lakes—its preferred habitat. Occasional sightings are still made in the North Island, but it is not clear whether these are stragglers from Australia or from the South Island. Almost certainly, no breeding populations of southern crested grebes remain in the north, although New Zealand’s two other grebe species are found there: the New Zealand dabchick and the Australasian little grebe. Like their southern relative, both species are uncommon.
While the southern crested grebe seems to have been present in reasonable numbers on Lakes Rotoroa and Rotoiti (now in Nelson Lakes National Park) in the 1800s, its numbers dwindled after the arrival of European settlers and completely disappeared sometime in the 1950s. Grebes were never established in historical times on other Nelson or Marlborough lakes, though they were occasionally sighted in such places as Lakes Cobb (Kahurangi National Park) and Chalice (Richmond Range).
As well as disappearing from Nelson and Marlborough, the southern crested grebe has suffered significant declines in Fiordland and Westland. The bulk of the small remaining population is located on the alpine and subalpine lakes and tarns of Canterbury and the northern McKenzie basin.
New Zealand’s grebes live in a challenging environment. The lakes they inhabit often partially or totally freeze in winter. Some lakes where I have seen a pair nesting in January are frozen solid in August, with ice thick enough to walk on.
One does not need to spend long in the South Island high country before being subjected to the blast of a gale-force nor’wester. The lakes on which grebes are found are subject to these intense winds for days on end, creating very rough and murky water conditions and making it difficult for the birds—which hunt small fish underwater, locating prey by sight—to feed successfully.
Severe storms cause lake levels to rise quickly, which poses a problem to grebes during the breeding season. Grebe nests are large, floating structures, often attached to tree branches or other vegetation close to the lake shore. The birds seem unable to effectively raise their nests above the rising water, with the result that they are sometimes flooded, and the eggs lost.
The southern crested grebe has coped with such hazards for many thousands of years, so why has it declined to the point where it is now classified as “vulnerable to extinction”?
Breeding failure appears to be the major problem, but before examining specific causes we should consider some aspects of the grebe’s life history.
In 1971, University of Otago zoologist Kaj Westerskov estimated that each pair of grebes required between 12 and 75 ha of lake habitat. He noted that birds in smaller lakes required smaller domains. Observations of grebe feeding suggest a reason for this result: the birds hunt near the bottom in water not more than five meters deep. Much of a large, deep lake is therefore unsuitable as a food source, while a shallow lake offers abundant bottom habitat for fish, and plentiful pickings for a diving grebe.
Some of the South Island’s glacially fed lakes, such as Pukaki and Tekapo, are unsuitable as the glacial flour makes the water too murky for successful feeding—though I have seen birds on Lake Benmore and some of the other hydro lakes in the Waitaki Valley.
The southern crested grebe is thought to be a long-lived bird, perhaps over 20 years. Because of the difficult conditions under which the birds live, their breeding cycle includes several special adaptations. They have a very long period in which they can breed—up to eight months. Even during harsh winters adults do not lose their breeding plumage. And although the grebe is not thought to be monogamous, I have rarely seen adults that were not in a pair.
Even during mid-winter on partially frozen lakes, I have seen pairs engaging in what appear to be courtship rituals, with the birds putting their necks together, then separating for a few minutes before displaying again. During this time they often make guttural calls to each other. Sometimes the birds are so close together that it seems—at least through binoculars—that a lone bird is sitting on the water.
Grebes do not normally begin to breed until October. Although reports of nests with up to seven eggs have been made, the nests I have observed have typically contained two to four. Another grebe adaptation is staged hatching of the eggs. The chicks emerge about two days apart, increasing the chance of survival of at least some of the offspring.
Young chicks ride on their parents’ backs and are capable of clinging there even during feeding dives. I have seen grebes carry two young on their backs, but it always looks to me as if this is a full load.
Even the youngest chicks appear to be good swimmers, and will transfer from one adult to the other without difficulty. They have a long period of dependence on their parents—up to 11 weeks. Both adults protect and feed them while they perfect their hunting techniques.
Given this high level of parental care, how is it that the grebe population is in decline? Human disturbance has to be seen as a major factor. Development around grebe lakes has resulted in the destruction of suitable nesting habitat, and these timid birds do not take kindly to power boats and jet-skis zooming past. I have been surprised when kayaking on Lakes Pearson, Lyndon, Selfe and Georgina that grebes in open water show clear signs of anxiety when approached, even at distances exceeding 100 m.
The activities of holiday-makers and fishermen during the nesting season can cause grebes to vacate their nests for extended periods of time. Although the nests are often well hidden, the parents will leave them with upon the slightest provocation.
I learned how sensitive they are to human presence when I was contemplating taking a photograph at Lake Selfe. As I was standing looking at the scene I became aware of the silhouette of a nesting grebe in a willow tree, 15 m away. I remained motionless, but soon the grebe left its nest and took up its distinctive zig-zagging swimming vigil beside the tree. I had to abandon my shot and leave the immediate vicinity before it would return to its incubation.
As well as being vulnerable to rising lake levels, southern crested grebes also appear to be sensitive to water quality. With the application of artificial fertilizers to farmland, the nutrient levels in the lakes often rise well above namrallevels, contributing to a decline in quality and reduced feeding success for grebes.
As with many other New Zealand birds, predators have also played a significant part in reducing the population. The ferret, common in the high country, is a competent swimmer and capable of removing eggs whole from grebe nests. At one time, southern crested grebes used to nest on shore, but with cattle and sheep grazing the lake edges and trout anglers seeking ever more out-of-the-way spots, most grebes have been forced to locate their nests on the water. Loss of eggs through wave action, either namral or generated by power boats, is higher now than in the past.
Nesting on water may also give grebes greater exposure to a namral predator, the eel. Chicks are particularly vulnerable. Even when a pair successfully hatch a chick, the chances of survival to adulthood are low. Predation aside, population records suggest that for young grebes to survive it is necessary to have two or three months of warm, stable weather conditions over the summer and early autumn, together with an adequate food supply. In many years, the weather simply does not cooperate.
It was once thought that the southern crested grebe was a weak flier—indeed, I have never seen one in flight. But a recent study conducted by University of Canterbury student Colin O’Donnel has shown that they are strong fliers, with speeds of between 45 and 60 km/h. Outside of the breeding period, when they establish and defend a territory, the birds are highly mobile, moving from lake to lake, though often staying for only a few hours.
Grebes are capable of travelling significant distances within New Zealand, and at some stage in the past must have made crossings of the Tasman from Australia to New Zealand. In recent years, Lake Forsythe, near Birdlings Flat, on Banks Peninsula, has become a favourite overwintering area, with up to 60 birds being present at one time. To get there from their breeding lakes entails a 190 km flight for grebes coming from Lake Alexandrine, and 140 km for those from the Ashburton lakes.
Will the southern crested grebe still be present in New Zealand in a hundred years’ time? This is a difficult question to answer. Although Westerskov documented a decline of 35-40 per cent in grebe numbers in Canterbury in a 30-year period up to 1970, his population estimate of 200 to 250 birds remains much the same today. Accurate figures are difficult to obtain, as there are no systematic counts being made over the whole country.
Grebe nests are great untidy piles of moribund vegetation, concealed around the edges of lakes. Although white when laid. the eggs quickly discolour to brown, for the birds cover them when they leave the nest. Although the parents are assiduous, mortality among young grebes is high, and the New Zealand population is only just holding its own.
Anecdotal evidence suggest that the grebe has managed to hold its own in Canterbury, and at present its high-country lakes appear to be its best hope for the species’ survival. One factor which has contributed to grebe success in Canterbury is the presence of willows on many lake shores—an example of human modification having a positive benefit. Willows have now become the preferred sites for nesting, with studies indicating that more than two-thirds of all Canterbury nests are sited among willows.
It is not difficult to understand the grebe’s preference for these trees. Their long branches hang down into the water, concealing the nest. As old trees fall, secondary root and shoot systems create dense tangles of foliage, which provide a buffer against wind and waves.
A number of Canterbury lakes have full or partial protections in place to assist the survival of the crested grebes. Some, such as Lakes Grasmere and Heron and the Maori Lakes, are part of wildlife refuges. But even at these places I have seen spent shotgun shells in the surrounding marshes, indicating that at least some members of the public are not observing theirprotected status.
At present, the southern crested grebe is in classification “0” of the Depai unent of Conservation’s scheme.
This means that the bird is threatened, though not yet endangered, within New Zealand, but that there are secure populations elsewhere in the world. Apart from the monitoring of some populations and attempts to educate power-boat users about the deleterious effects of their activities on shy birds, the grebe is being left to its own devices. But with only a couple of hundred members, the grebe’s grip on survival is tenuous.