Shorebird under threat
Mother’s love and protection just aren’t enough these days if you happen to belong to one of those shorebird species which nest on open beaches. Predators, recreational vehicles, storms and beach-front developments threaten not just this variable oystercatcher chick but the very survival of several other species.
In 1970, I remember being taken to a wild sandspit 60 km north of Auckland as the oyster‑catcher flies. It was an expedition to study the area’s undisturbed bird life and vegetation and to enjoy the natural rolling sand dunes facing the Pacific. Since no road access to the spit existed, we had to row across a narrow harbour entrance at slack tide to get there.
The area was not pristine: there were rabbits aplenty, a few wilding pine trees, pampas grass and other weeds, but it was largely unspoilt by human intrusion. Typical native plant cover of spinifex, pingao, pohuehue, beach convolvulus, shore rocket and sea radish stabilised the dunes and brightened the foreshore. New Zealand dotterels and banded dotterels were common along the beach flat and among the fore dunes, and several pairs of variable oystercatchers peep-peep-peeped stridently to announce their displeasure at being disturbed.
Overhead a pair of Caspian terns with conspicuous black caps and scarlet bills drew attention to themselves with loud, harsh squawks. A small skein of pied stilts, their red legs trailing straight out behind, flew along the sandflat and landed at the water’s edge, mingling with a large mob of South Island pied oystercatchers that were already probing the soft sand for shellfish, worms and crustaceans. Further along the beach, a flock of over 100 bar-tailed godwits were feeding in the company of a solitary whimbrel, a larger bird with a long curved bill which is a regular straggler to our shores in summer.
This sandspit, Mangatawhiri as it was then known, was a wild place for the birds in every sense, a place where nature alone held sway. Wind and wave had taken several large bites from the fore dunes, and a litter of large logs cast up above high tide into these amphitheatres showed the force and size of ocean swells that frequently raked the seaward side of the spit. Being built entirely from mobile sand, it was an inherently unstable peninsula, hostile in almost every way to human habitation.
Hostile, but not impervious.
Before long a developer had acquired the spit, renamed it Omaha (an old name for a local parish) and put in an access causeway across the inner harbour. Gradually—as is the way of all subdivision—the landscape was modified to suit the newcomers. The rolling dunes were stripped of their stabilising vegetation and reshaped to give sea views to houses further from the beach. A massive sea wall was erected (and smashed to matchwood during a storm within a year of being built) to arrest sand erosion associated with changes in the hydrology of the area—in part brought about by the causeway that opened up the place.
As people moved in, the birds retreated, shifting closer to the tip of the peninsula, until now, with the final stage of subdivision pressing close to the last remnant of wild open space, they cling to a precarious existence.
Now, in place of spinifex and pingao, Omaha boasts the Astroturf of tennis and bowling club and the manicured greens of a golf course. In the space of 25 years a wildlife retreat seldom visited by people has become a housing estate where the predominant animal species are cats, dogs and the birds of suburbia:mynahs, blackbirds and sparrows.
It is a common enough pattern. Open coastal landscapes have given way to beachfront subdivisions in Papamoa, Pauanui, Pukehina, Whitianga, Waikanae, Maketu, Langs Beach . . . the list is long.
The simple fact is that humans and nesting shorebirds do not mix. The incompatibility is particularly acute because of the type of nests made by these birds. In general, the style and structure of a bird’s nest reflects the stresses its chicks are likely to endure. Some, mainly small, birds make complex nests that give great protection from the elements to large broods of chicks that are tiny, blind, bald and helpless when hatched. Larger birds lay fewer but proportionally larger eggs and their hatchlings are sighted, well covered in down and able to stand within an hour or so of emerging from the egg. As they are more robust, these chicks need less physical protection, and the nests that hold them are usually simple or, in the case of shorebirds, quite rudimentary.
Frequently they are little more than a depression in the sand where the parent has shuffled its body. They are usually situated on the terrace of sand and beach debris pushed up by exceptional storm waves. Higher ground on the fore dune slope, though less vulnerable to storm waves, is unsuitable because the dune sands are unstable. The bird’s reproduction is adapted to the vagaries of the weather and the chance that in some years abnormal storm waves will sweep their nests, eggs and chicks away. After such a catastrophe a new scrape is easily made and pairs typically lay replacement eggs two or three weeks later.
In January 1997 just such an event happened, when Cyclone Drena hit Northland. While campers were hastily pulling down their tents and fleeing the high winds and rain, a nesting colony of white-fronted terns at Papakanui Spit, on the south head of Kaipara Harbour, was being wiped out.
In every way it was a freak event. The predicted high tide of 4.5 metres for January 9 happened to be one of the highest for the year, and it occurred at midnight as Drena was approaching the coast. Extreme low pressure and storm-force westerly winds associated with the cyclone raised the high-tide level to over five metres and produced huge breakers that swept across the upper beach terrace and into the sand dunes behind. The colony of 1800 adults, 400 flightless chicks and some 300 unhatched eggs was obliterated.
Remarkably, a good number of the more mature chicks were located the next day some distance away on slightly higher ground where they appeared to have been swept by the destructive seas, and these youngsters would all have been reunited with their parents.
For nesting birds, a storm in November is probably not an irretrievable loss, but if such a storm occurs late in the season there may be insufficient time before the onset of wintry weather to raise a late brood successfully. Indeed, before the arrival of humans, failure to breed in one season due to storms wiping out most of a species’ nests was probably of only minor consequence to the long-term population structure of the birds. Today, now that the numbers of some shore-nesting birds are so low and suitable nest sites so scarce, it is critical.
Predators are a biological fact of life, and for New Zealand shorebirds most attacks have traditionally come from the air. Predatory scavengers like black-backed gulls and, in the south of the country, skuas, regularly rob eggs and prey on defenceless chicks when the parents are off the nest. Harriers will also take the young of ground nesters.
The simplicity of shorebird nests is partly a camouflage strategy to conceal their contents from flying eyes. Fairy tern nests, for instance, are never anything more than an unadorned depression in the sand. To accumulate nesting material such as twigs or the leaves and stems of dune grasses would only draw attention to the scrape. Fairy tern eggs are off-white to very pale grey, with a few nest scrape, but in cleaner areas, nests of the same birds will have no plant matter at all.
Young chicks also need to avoid notice. Their best defence is to remain motionless and lie low on the sand so as not to cast a shadow. They are also cryptically coloured to make them difficult to spot.
As the chicks grow, they are more difficult to conceal but just as vulnerable to predators. Even their parents are no match for determined attackers from ground or air, but they do have an effective behavioural technique for reducing threats to their chicks. If a predator approaches the nest, the parent utters loud alarm calls to warn the chicks to remain absolutely motionless. It then proceeds to attract and divert the predator’s attention with calls and what is known as the “broken-wing display.”
Prostrating itself on the ground within clear sight of the predator, the adult bird stretches out its lower wing awkwardly to give the impression that it is disabled. By presenting itself as easy meat, the bird encourages an attack on itself rather than on the chicks.
As the predator focuses on the parent, the bird flaps and stumbles across the sand, pretending that it is trying to evade capture as it draws the threat away from its brood. Once it has established a safe distance, its “broken wing” suddenly makes a remarkable recovery and the bird flies off.
With the arrival of humans to areas used as breeding sites by shorebirds, the threat profile to these species has been drastically altered and increased. Now their main enemies are ground-based, not aerial. Black and brown rats, unintentionally introduced by early settlers, have become a menace to all birds. When rabbits, released for meat and fur, multiplied so rapidly that they became a pest, their natural predators in Europe, ferrets, stoats and weasels, were released to control them. But these mustelids have found that New Zealand’s native birds are just as good to eat as rabbits, and often easier to catch.
Cats, escaping into the wild, have added yet another dimension of tooth and claw to the nightmare being faced by our native birds.
Against this mass influx of new predators the shorebird’s natural defences and deceptions have proved completely inadequate. The broken-wing display may distract a mammalian predator for a short time, but since ground predators have a strong sense of smell as well as keen eyesight for movement, they soon flush out the nestlings.
Even domestic pets can be a menace. Cats are born hunters, of course, but unruly dogs can cause real mayhem if allowed to run free at night. There are many recorded incidents of uncontrolled domestic dogs slaughtering large numbers of native birds for food or sport.
Even well trained dogs can seriously disrupt nesting birds. Every beach in New Zealand on which dogs are regularly exercised has effectively become a non-breeding area for shorebirds, for they can never brood their eggs in peace. Even when they are just feeding at other times of the year, they are relentlessly pursued and put to flight while the owners admire their dogs’ athleticism, never realising the damage being caused.
The variable oystercatcher is one species which has suffered on account of canines. A handsome black shoreline wader with pink legs and a long, bright-red bill, it is found on beaches all around New Zealand, but its headquarters are in the northern half of the North Island. Sonic people consider the bird an icon of northern shores.
Unlike the South Island pied oystercatcher, which breeds along the shingle banks of rivers and migrates to the coast outside the breeding season, the variable oystercatcher spends all of its life along the shore and attempts to breed there. In the greater Auckland region pairs of variable oystercatchers are still regularly seen on many beaches, but for the last 10 to 20 years a pair with chicks has been an uncommon sight. Only on offshore islands and along the shores of regional parks where dogs are banned are these birds still able to breed freely.
For the most part, dog owners’ obsession with the rights of their dogs in places that should properly be regarded as the breeding preserves of birds is denying the public the delight of seeing adults caring for their chicks.
At Omaha, where a small area close to the spit’s tip has been set aside and fenced off as an oystercatcher and dotterel breeding ground, only four young were fledged last year by nine pairs of breeding oystercatchers. Under favourable conditions these birds often raise three young per pair.
On one occasion, as I watched the birds through binoculars from the top of a small sandhill, I was startled by a pair flying towards me just above ground level and uttering loud alarm calls. They were in angry pursuit of a cat, attempting to drive it out of the fenced enclosure. It was a sad demonstration of the difficulty of setting aside land for birds next to housing areas where domestic pets can roam.
Over the last decade, even remote nesting areas have become vulnerable to human disturbance. Papakanui Spit, at the entrance of Kaipara Harbour, 55 km up the beach from road access at Muriwai, is well off the beaten track. However, the growing popularity of fourwheel-drive, off-road vehicles”Remuera tractors,” as some rural cynics refer to them—has opened up even these backwaters to destructive pressures.
Fishing parties deem that the more remote the location the greater the chances of catching prize fish, and South Head is becoming such a haunt. Some stay overnight or camp for the weekend. They pitch their tents and drive their vehicles above the strand line on the upper beach terrace, the same areas the birds use to roost and to nest—and the birds are ousted.
Some visitors arrive on farm bikes and enjoy putting them through their paces among the dunes. Birds are put to flight, nests and eggs are run over and dune stability is undermined. Dogs are often brought along on these expeditions, and while the owners look to their lines, the curs kill chicks and drive brooding parents off their nests. Uncovered eggs quickly become overheated on bright sunny days, and sufficiently chilled on clear nights to stop further development.
A further problem innocently created by the anglers, picnickers and overnight campers is that they encourage black-backed gulls to the area. Attracted by discarded food scraps and the heads and frames of filleted fish, these scavengers now frequent areas like South Head in much greater numbers. When the itinerant fishers depart, the gulls’ attentions may turn to the eggs and offspring of other birds.
Fortunately for the birds, some humans are sufficiently troubled by their plight to want to assist. The Department of Conservation, the arm of government officially charged with managing endangered species, does what it can, but its limited resources are spread thinly across the whole gamut of species in every habitat.
Managing bird recovery has long been a saga of clever schemes and sad mistakes, last-gasp rescues and missed opportunities, and there is always controversy over what level of intervention is appropriate.
The rescuers must constantly be alert to the effects of their own activities. For example, the measures they take to protect nest sites from either predators or natural disasters may themselves be intrusive and cause the birds to desert their eggs or chicks.
So while the conservation department calls the shots, it is dependent on the efforts of dedicated volunteers from the ranks of such organisations as the Ornithological Society of New Zealand and the Royal Forest & Bird Protection Society to do much of the legwork.
Gwenda Pulham, a school dental nurse (“What else could I be with a name like that?”) admits she is nuts about fairy terns—the most endangered of New Zealand shorebirds—and spends most of her spare time labouring on their behalf.
Her bird work stems from hearing a talk at her local library by a member of the Miranda Naturalists’ Trust. She joined the Ornithological Society in 1976, and then it was but a short step—guided by her girlhood interest in things maritime—to shorebirds.
“One particular episode over Christmas 1977/78 got me fired up about fairy terns,” she says. “I was up staying with my sister, who lived near the mouth of the Waipu River, and nearby was a large colony of white-fronted terns and a few fairy terns. One afternoon I watched a guy on a trail bike roaring around the area where a pair of fairy terns was nesting. It looked as though he had run right over their nest, but when I later got across the river and checked, the tyre tracks were a hand-width away. But he might as well have crushed it, because the birds abandoned their eggs and renested nearby.
“A few weeks later I again watched, helpless, across the river as a cricket game attached to a big New Year’s party spilled out across the beach. This time the pitch was right where the nest and eggs were, and I couldn’t help thinking that surely those little birds should be able to nest somewhere in safety.”
The last five years have seen Gwenda particularly active in the birds’ service. Over their breeding season she usually makes at least two forays a week to one or more of their known nest sites (Waipu, Mangawhai, Papakanui Spit) or maybe checks a site such as Pouto where they could possibly breed.
“Fairy terns seem to need an undisturbed spit with fast-moving water on one side and an estuary on the other,” she explains. “I help wardens monitor breeding birds on nests, assist with putting up signs and fences trying to ensure that the birds remain safe and undisturbed, keep an eye on chicks once they become mobile, carry out bird censuses, sometimes just cook the DOC people a meal.”
Despite the labours of Gwenda Pulham and others, not all hazards can be avoided. In late November 1997, the nest of one of the only two breeding pairs at Papakanui was “sanded.”
“Obliterated,” Gwenda says. “A strong wind blowing over dry sand can shift a metre-high dune in just a few hours. And that’s what happened here—the nest was simply buried.”
One of this pair of birds was lucky even to be alive—the sole survivor of the 1992/93 season at Papakanui. “The first nest I found that year was sanded; the second and third were destroyed by the sea, and the fourth—a renest—was going to be destroyed by upcoming spring tides,” says Gwenda. “We took its two eggs and placed them under a pair that had been incubating what were obviously infertile eggs at Mangawhai for 42 days, almost double the usual incubation period.
“From the new eggs they got a chick after 55 days total sitting—equivalent to a woman being pregnant for 22 months! Over the last three summers, that chick has come back to try and breed at Papakanui, where it was conceived.”
During the winter, Gwenda’s trips drop back to two or three per month, just to keep an eye on her beloved fairy terns, which often gather at Tapora in the Kaipara. Over September and October she likes to find out where the birds are moving back to, and tries to figure out what might happen in the upcoming breeding season.
She hasn’t a clue how many hours she spends or how many kilometres she clocks up: “It doesn’t matter. It’s my hobby, my passion, my battery recharge. I’m outside, doing something worthwhile, learning a lot of interesting stuff and meeting some great people.”
John Dowding, an independent researcher, is convinced that predation is the major factor in the decline of shorebirds. But he has noticed that the dynamic between birds and predators varies from species to species and place to place.
He rattles off a list of birds which have coped, and those which haven’t: “The New Zealand shore plover was once widespread around the South Island, but, due to cats and rats, it was exterminated by 1872. In the 1880s, mustelids arrived in the south and New Zealand dotterels were quickly wiped out, but banded dotterels were OK and still are. Wrybills, which nest on the beds of braided rivers in the South Island but spend their winters on shores about Auckland, are interesting in that their numbers have stayed at about 5000 for years. Many breed on islands in the rivers, which presumably gives them some protection. Pied stilts are so closely related to black stilts that they can interbreed, but pied stilts somehow cope with predators and number tens of thousands, whereas black stilts total about 50.”
John’s particular interests are variable oystercatchers and New Zealand dotterels. He is trying to find out what predators attack these species in different parts of the country and what impacts the predators are having on various populations. On Stewart Island, a subspecies of New Zealand dotterel numbers only 110 individuals—but that’s up from 60 only six years ago.
“Down there, cats take birds on nests at night, and since males mostly do the night-shift incubation, there is a shortage of males in the population. As a result, females pair up, lay infertile eggs and sit on them forever. And the males are strictly monogamous. It’s a crazy situation!”
Further north, different predators are the problem. In 1995, on Waiaua Spit, east of Ohope, the remains of 11 New Zealand dotterels were recovered from a stoat’s den. They had been taken over no more than two months. When eight captive-reared juvenile dotterels were released at Omaha, stoats got six of them within two days. Variable oystercatchers—larger, stronger birds than dotterels—fare better against predators, and their numbers are increasing slightly.
These days, according to Dowding, many eggs of ground-dwelling birds, including those of many of the smaller shorebirds, are eaten “almost as soon as they are laid.” And one of the main culprits is an unexpected predator: the hedgehog. “There are surprising numbers of hedgehogs behind beaches. Along a kilometre and a half of dunes at ‘Fawharanui Regional Reserve, north of Auckland, 400 hedgehogs were trapped over two years, and enough still remained to devour all the dotterel eggs. I’ve filmed them eating eggs, tapping with their teeth until they have made a hole, then biting the shell away—they are a very underrated predator.” The other main egg predators are cats and stoats.
Whether a shorebird species is going to survive long-term depends on a complex mix of factors, says Dowding: how many chicks fledge, how many of them survive to breed, and how long the adults live.
“It takes years to gather reliable data, and for many species we don’t have that yet,” he explains. It is now known, for example, that the survival of adult New Zealand dotterels is high, but they don’t fledge enough chicks. “At least we have identified the bottleneck for this species, and can work on improving breeding success,” he says. “Even then, we may find that a species has the potential to increase, but its habitat is being degraded to the point where it can’t realise that potential.”
The outlook for the 1500 remaining New Zealand dotterels is not good, says Dowding: “Eighty per cent of them are on the North Island east coast between North Cape and East Cape, the area in which most human population is concentrated and where most coastal development occurs. Back in the 1940s, Whangamata had a thriving dotterel population, but now there is not one remaining. It’s a story that has been played out many times and is still running. Sandspits at Ngunguru and Matarangi are dotterel habitats—both are under threat from development.”
What can be done? Even with the best efforts of volunteers and wardens, it is impossible to keep nests and breeding birds under 24-hour surveillance. All too often, disasters occur during periods when nests are not being watched, and it is critical to the recovery programmes to identify causes of nesting failures so that preventative action can be taken.
Experienced observers can frequently identify likely culprits of chick or adult predation by telltale signs left behind: footprints, feathers lost in a struggle or carcass remnants. But sometimes there are no clues at the crime scene. Video surveillance cameras have been employed, but their utility is limited. While they have proved valuable in identifying cats as predators on Caspian terns at Mangawhai, so enabling DOC to take appropriate measures, they would not be particularly useful at Papakanui Spit. Some newly hatched chicks (but not eggs) have disappeared from nests there, but by the time the chicks are even six days old they are moving about well beyond the vicinity of the nest and out of sight of any camera trained upon it.
Ringing nest sites with traps has been useful for controlling stoats and ferrets, but catching domestic pets causes an outcry from owners and costs the wildlife goodwill.
Erecting fences and placing public information panels around the nest sites of endangered birds is often useful in advertising their general location to passers-by, but, of course, such measures are ineffective in keeping out animals. At some sites temporary “no-go” areas are being established through the breeding season.
It is not a bright prospect, but not one of unremitting gloom, either.
In the last few years, high hopes have been held and bold attempts made to reintroduce one shorebird species, extinct from mainland New Zealand for over 100 years, back into the Hauraki Gulf. The shore plover—represented in the wild by only 120 birds on South East Island in the Chathains—was bred in captivity and released on supposedly predator-free Motuora Island near Kawau.
However, the wildlife officers didn’t count on moreporks, which killed most of the first consignment. The moreporks were removed, but, perversely, subsequent releases have forsaken the confines of the island for predator-plagued mainland beaches, where most have presumably perished.
The plan now is to try to confine birds on Motuora until they have bred, then release the young, which are more likely to remain where they were born.
Back at Omaha, the shorebirds’ fortunes may be changing, too. New houses are still being built, but the plight of the birds has taken root in the local conscience—pricked, perhaps, by the fact that the seven or eight pairs of New Zealand dotterels trying to breed there have not succeeded in raising a single chick in the last six years.
The Omaha Residents and Ratepayers Society, the developer, Forest & Bird, DOC, the Rodney District Council and concerned locals have all joined forces to help the birds. The developer has put up better fencing at the end of the spit.
Locals are trapping predators. Forest & Bird is paying for a warden to watch over the fenced area which the birds inhabit. DOC and the council are producing better signs and information brochures.
John Dowding, who has been monitoring the birds at Omaha for years, is now cautiously optimistic. “Once locals understand the problems, it’s surprising how willing many people are to help, and surprising what they can accomplish. I get calls from people all over the place reporting seeing dotterels and wanting to know what they can do to assist them. Ten years ago nobody knew what a dotterel was.”
It will require the efforts of the Omaha group multiplied a hundredfold, however, if the most endangered of our vulnerable little shorebirds are to have a secure future around our coastlines.
A miracle, perhaps, but one in which we can all play a part.