Birds in Their Habitats

by Ian Fraser

  The Lord Howe Island Woodhen is an engaging olive-brown bird the size of a small chook. It potters about, poking its long bill into ground litter and rotting logs to extract worms, grubs and arthropods. Its response to an unfamiliar object is likely to be to wander straight up to it, no matter if the object happens to be a cat, dog or hungry sailor or settler. This is one of the problems of evolving on an island where there were probably no significant predators for most of your history there – you don’t have any appropriate defences or reactions. Cats, dogs, pigs and settlers depleted the numbers until, by the late 1970s, there were fewer than 40 woodhens left, restricted to the remote peaks of Mount Lidgbird and Gower. When a survey in 1980 found just 15 individuals, drastic action was required, and thankfully was taken. Birds were taken into captivity, where fortunately they were quite willing to breed. At the same time, urgent research into the several possible causes of the continuing decline identified feral pigs as the key threat, and their elimination was commenced. The overall program has been a rare and impressive success story: woodhen numbers are up to 250 birds, which, with a required territory of 3 ha per breeding pair, is probably the most the island can carry (e.g. Frith 2013). I have met them carelessly crossing the road from the airport into the adjacent heath, forcing us to stop our hired bicycles, rustling under the bushes outside the island bottle shop (I can’t now recall why we were there) and exploring the lawns of our guest house.

  It is no coincidence that such a high proportion of recent bird extinctions has been among the island rails, and that so many of them are flightless. The woodhen is in the same genus as the Buff-banded Rail – it is a matter of some debate as to just what that genus is, but it is generally agreed that, whether it’s Gallirallus or Hypotaenidia, they’re both in it. This is relevant because the Buff-banded Rail is an amazing wanderer across watery wildness. It seems as though there’s something in its genes or psyche that drives it to take off and head out to sea, or perhaps it is just congenitally careless about taking to the air in storms. This is despite the fact that we don’t often see it flying – it tends to skulk around thickets and wetlands. But fly it most certainly does: there are (or were) at least 22 subspecies on islands of the south-west Pacific, from the tropics north of the Philippines to the sub-Antarctic (though the Macquarie Island subspecies is no longer with us) and east to Fiji, Samoa and Tonga. This is an astonishing feat of distribution in a bird not noted as a strong flyer, and it is not at all surprising that it or a closely related ancestor reached Lord Howe Island at some point – indeed, in recent decades, newly arrived Buff-banded Rails have also started to build a substantial population on the island (Hutton 1991).

  Island breeding colonies: from Fernandina to Cape Town to Victoria to Chile

  I had the good fortune of meeting the Galápagos Flightless Cormorant at Punta Espinoza: the only permitted landing place on Fernandina, the western-most and youngest island of the archipelago. The birds, numbering only a few hundreds, live only here and on adjacent Isabela. Volcano Cumbre is still very active, coughing up lava every few years, and the land surface is dominated by black volcanic rock, with smooth swirls in parts and jagged edges in others. Clusters of Lava Cactus, one of the first colonisers of newly cooled land in the Galápagos, sprout seemingly (and actually) from the rocks. Tight masses of short thick somewhat phallic stems form dense colonies: the packed spines are bright yellow when young, darkening with age. Hundreds of Marine Iguanas, dark as the lava, sprawl in piles to warm in the sun between sessions of browsing on algae in the cold sea currents.

  Why give up your wings?

  There are, it seems to me, a couple of reasons why a genetic adaptation, such as flight, might be subsequently lost, despite the obvious advantages it confers. One eventuates if the species begins to ‘experiment’ with a new lifestyle that interferes with flying, making it first difficult, and eventually impossible, as the new skill becomes more important than the old one. One example is that of penguins, which became so adept at ‘flying’ underwater that their wings became ultimately suitable only for flight in that medium, rather than in the air. Another is the ratites – the giant ancient Gondwanans including ostriches, emus, and so on – whose ‘experimentation’ was with progressively greater size for greater safety, until the universal cut-off point of 15 kg was reached, beyond which true powered flight becomes mechanically impossible.

  The second possible reason why the power of flight may be forgone is represented by a conundrum: what if the environmental pressures that led to its evolution disappeared? If a bird found itself in a situation where it had no enemies, then the cost of maintaining its flight might eventually prove to be not worthwhile. This would be especially true if there was nowhere to fly to. The answer to this somewhat Gollumesque riddle is the situation facing a group of probably unwilling colonists on a remote island. As we have previously observed, flight on a small island may in fact be a hazard, with the risk of being again blown out to sea. Many different unrelated groups of birds, in addition to the rails, have flightless members on oceanic islands (e.g. the New Zealand Kakapo is a parrot and the Dodo of Mauritius and Rodrigues Solitaire were pigeons).

  The Galápagos has a flightless cormorant and there are two flightless teal species on New Zealand islands, and a flightless steamer duck on the Falklands (as well as a couple on the mainland of far southern South America). To a weakly flying waterbird, large alpine lakes might be considered islands in a hostile sea of heathland, and there are two flightless grebes on high-altitude Andean lakes in Peru, including on the huge Lake Titicaca (see Photo 13). Other species, such as the Kagu of New Caledonia and the mesites of Madagascar, have been isolated for so long that their relationships are obscure, though the Kagu seems to be closest to the equally enigmatic Sunbittern of South America. The mesites, which are almost flightless and seem to be evolving in that direction, may be distant pigeon relatives, but the necessary DNA work appears still to be done.

  Tragedy after tragedy has ensued when an enemy – inevitably people and their animal associates – has suddenly appeared in the habitat of a bird that has forgone its best protection: flight. Victims have included the moas, the elephant-birds and the Dodo, as well as the lovely snowy Lord Howe Swamphen and the numerous other flightless rails.

  These cormorants are the world’s largest: a metre long, dusky brown with a long tail and bright blue eyes. They nest on a sandy-rocky spit, with the substantial seaweed-pile nests scattered just above the high tide mark so that each is out of reach of its neighbours. When the non-brooding partner comes ashore from fishing, the birds reinforce their partnership with extravagant head gestures and gnarring displays. Like other cormorants, they lack waterproofing oils in their feathers – oil is lighter than water, and would make their underwater fishing too difficult – so must hang their wings out to dry, when their puny nature becomes evident. It is obvious these wings could never carry them through the air (see Photo 14).

  This colony numbers only a dozen or so pairs, but seabird nesting colonies can be huge. Lambert’s Bay is an industrialised little fishing town on the west coast of South Africa north of Cape Town, but is notable for hosting a massive colony of Cape Gannets. The access to the well-managed and well-interpreted colony is very easy to miss: a little back street leading past a factory and warehouses to a carpark from where we walk across a causeway to a small island – imaginatively named Bird Island – where a hide (with a window downstairs and open on the first floor) looks straight into a solid mass of black-winged white birds with yellow-buff necks and caps. They press in (some 30 000 of them when I was there, according to the chalk board in the hide) as densely as they can fit. But seabird colonies rarely comprise just one species. At Lambert’s Bay, behind the gannets and among the Cape Fur Seals, are breeding Cape and White-breasted Cormorants and Kelp Gulls, and Crowned and Bank Cormorants and Hartlaub’s Gulls also breed on derelict boats in the adjacent harbour.

  In south-western Victoria, the pretty little town of Port
Fairy has more historic buildings per square metre than almost anywhere in Australia. It also has an even greater treasure, which, like Lambert’s Bay’s treasure, is on a little island joined to the mainland by a causeway. Among the grass clumps on Griffiths Island are up to 100 000 burrows excavated by Short-tailed Shearwaters (also widely known as Muttonbirds for their contribution to a long-standing industry of harvesting the oil-rich chicks on islands off Tasmania). One parent broods in the burrow, while the other fishes at sea – each day at dusk large numbers of the foragers come home to change shifts. If you wander down to the viewing area around sunset you can look out to sea and see dim hints of movement on the horizon, like distant swarms of insects or perhaps just a trick of the fading light and straining eyes. When it’s almost too dark to see, and the more impatient or uninformed visitors have wandered off for a meal, suddenly the air is full of large dark bodies plummeting to earth and the burrows, being greeted by a great chorus of breathy squeals from underground. It’s a strangely moving experience.

  Across the Atlantic from Lambert’s Bay and on the far side of South America, Puñihuil is a small fishing community on the wild Pacific coast of the island of Chiloé in southern Chile. Assisted by the Alfaguara Project (a marine conservation organisation focusing on the Blue Whales that breed in these waters), the local fishermen take visitors out in open boats to sail around the three little islands in the mouth of the bay. It is a spectacular experience, with the skill of the fishermen holding the boat seemingly perilously close to the rocks shrugging off the waves, and the cacophony and wild reek of the nesting colonies merging with the thump and hiss of pounding water. This is the only place where cold-water Magellanic Penguins and tropical Humboldt Penguins breed together. They are joined by four cormorant species, the stars of which for me are the Red-legged Cormorants, which I reckon to be the world’s most beautiful – ash grey with bright red legs and red-based yellow bills, a big white neck patch and silver-spotted black wings. Unlike either the scattered Fernandina Flightless Cormorants or the crowded Cape Gannets of Lambert’s Bay, Red-leggeds’ nests are just out of pecking distance of each other, which is more the norm in such colonies. Additionally, the islets support breeding Kelp Gulls, Kelp Geese and Fuegian (Flightless) Steamer Ducks.

  The basic reason for such colonies is simple necessity – there are finite suitable breeding sites, which for safety are on islands or cliffs, so they must lump in with other individuals and species. Overall, some 13% of bird species nest in colonies, but over 90% of seabirds do so. There are specific advantages too, though. For instance, colonies can provide group surveillance and defence against predators. By having huge numbers of eggs available at once, they can make it impossible for predators to take them all; in this case, the best sites will be those in the centre of the colony. But – and, of course, there must always be a ‘but’ – every strategy has a disadvantage. If there were a perfect strategy everything would use it! Problems associated with colonies include the fact that they are so easy for a predator to locate, shortages of nest sites and building materials and potentially of food to sustain a large number of mouths. Birds such as gulls threaten their neighbours with cannibalism, and disease and parasites spread very rapidly. The risk of wasting effort (often an entire day’s work at sea) in mistakenly feeding the neighbours’ offspring is perhaps the greatest of all. All colony-dwellers must be able to recognise their own eggs and young among the hordes, by location or voice.

  Chile’s Chonos Archipelago: prolific seabirds

  The Coastal Cordillera of Chile is a less lofty range of mountains running parallel to the Andes, but nearer to the coast. Between the two ranges is the huge and immensely fertile Central Valley from where pour Chile’s excellent wines. The cordillera runs into the Pacific just south of Puerto Montt – Chiloé Island comprises its peaks protruding from the sea. South of Chiloé the cordillera continues as the complex scatter of islands that make up the wind-hammered Chonos Archipelago. Vessels, from fishing boats to cargo ships to luxury cruise liners, ply the channel between the Archipelago and the snowy Andes peaks and glaciers that line the shore. Unless the clouds are lying on the sea so that islands and volcanoes are behind a densely opaque curtain, the views are superb, and the channel waters are alive with birds. Huge flocks of Sooty Shearwaters float in rafts on the sea, pattering across the surface with a very audible rush of water and soaring just above the waves, sliding across the bows of the ship. Pink-footed Shearwaters are more likely to be single, but are in pretty much constant view. Less common petrels (the Family that includes shearwaters) such as chequered Cape Petrels and palest grey stocky Southern Fulmars appear as luck determines. Enormous louring Southern Giant Petrels, big dark solid White-chinned and Westland Petrels, as well as some tiny ones in the vastness, delicate Wilson’s Storm Petrels and chunky Magellanic Diving Petrels, all come and go for as long as you can brave the wind in your eyes. And, from time to time, the vast and utterly majestic form of a Black-browed Albatross soars effortlessly across the grey heaving world.

  Wind soaring

  But when we turn into one of the fjords that indent the coastline, something peculiar happens – all the birds disappear. Not for them the sudden calm of the sheltered inlets: they crave and need the wind to ride upon. Indeed, both petrels and albatrosses seem to have arisen some 40 to 50 million years ago in the vast southern oceans, where the winds never rest. If the wind falls below ∼20 km/h, an albatross must wait on the water. Although shearwaters and other petrels in particular can fly hard and fast when they need to (especially during migration), for the most part they let the wind do the work for them. To watch a shearwater or albatross delicately slice the length of a wave top with one wingtip, then swerve through 180°, swing up high from the water, and suddenly be gliding low and fast over the surface again a couple of hundred of metres away, without once flapping, is to doubt one’s eyes.

  The secret is in those amazing wings. All of the birds we have just watched, or at least all the bigger ones, have very long slender wings (‘high aspect ratio’ in aerodynamic terms), with each square centimetre of wing carrying only a very small weight (‘low wing loading’). This is the perfect shape, theoretically and practically, for slow flying without crashing, and for soaring. Soaring is sometimes dismissed as just a sideshow to true powered flight, but in reality it is very complex behaviour indeed, and can be seen as the epitome of flight, achieved in all the long history of wings by very few, mostly large, birds and pterosaurs. Indeed, some ancient giant pterosaurs and birds could soar but could no longer truly fly. Soaring involves using the energy in the surrounding air to stay aloft, while expending very little of your own energy. Some land birds use warm air columns (‘thermals’) such as may be found rising over sand dunes or even buildings to achieve great altitudes from which they may glide, slowly descending to the next, or simply soar in circles watching for prey. They may also use wind deflected upwards by a dune or mountain range to the same effect.

  The Chonos Archipelago seabirds, however, are using a different energy source: the layers of wind over the sea blowing at different speeds at different heights. Simplistically, the layers closest to the sea surface are moving more slowly due to friction; waves increase the effect. The bird uses its wings and the relatively light wind close to the surface to lift itself off the water (often aided by some running on the surface), then climbs slowly through the layers into the wind to gain altitude. By swinging through 180° and plunging down through the layers again, it can gain energy as it goes. An albatross or shearwater can keep this up for days and thousands of kilometres, flying across the wind. And, as ever, there’s a ‘but’.

  The world’s sole tropical albatross, the Waved Albatross, breeds only in the Galápagos, and only on the island of Española (well, actually, a few dozen also breed on the little island of La Plata, closer to Ecuador – but that’s all). The cold waters are rich in food and the trade winds that blow from March to December keep the albatross aloft. In January and Fe
bruary, however, the winds drop and the albatrosses must move to cold Humboldt Current water off Peru and Ecuador. The problem comes when they want to take off from the ground at the nesting colony – and this is why they only nest on Española, a dot on the north-eastern edge of the Galápagos. Their wings (as with any high aspect ratio wings) are simply too long to flap without bashing into the ground, so they must run from the nest to the cliff edge, and hurl themselves off into the wind. Only on Española is there enough flat land to support a colony, and near enough to a cliff edge that faces into the prevailing wind. All of life seems to be about trade-offs!

  Other memories of oceans and islands

  Like droplets of spume drifting ashore from a wave destroying itself on granite rocks, a few arbitrary images of the sea and its islands:

  • Standing on the deck of a small cruise boat, with less than 20 of us aboard, we are sailing between islands in the Galápagos. Overhead a small flotilla of black Magnificent Frigatebirds floats effortlessly: males with a purple sheen to the neck feathers and flaccid red throat pouch, females with white throat feathers. They are huge, with a span of well over 2 m and long forked tails, slender wings angled into an ‘M’. For as long as they accompany us, benefiting from the updraft of air from our passage, not one flaps its wings. Not once. A female descends so that she is sailing alongside us, one alert eye level with mine and watching me.

  • Another experience of watching soaring seabirds at eye level was while walking the Malabar Cliffs on the north coast of Lord Howe Island. Here the stars are the beautiful snowy white Red-tailed Tropicbirds, which breed on the cliffs below us in huge concentrations and drift in glorious parade along the cliff face, pairs performing their mesmerising courtship dance. In these flights, one bird drifts along while the other ‘stands up’ on the air, pushing so that it moves backwards, while each points its tail towards the other (see Photo 15).