Birds in Their Habitats

by Ian Fraser

  • Pisagua, on the desert coast of far northern Chile, is a town of ghosts. Once a bustling port with 10 000 people and a concert hall that drew world-class performers, now mostly empty with a couple of hundred people relying on the fishing. Moreover, a series of 20th-century brutal military dictatorships used Pisagua as a prison camp for non-criminals – gay men in the 1920s, communists in the 1950s and various leftist opponents of the regime in the 1970s and ’80s. Many are buried outside the town. The cold Humboldt Current, bringing nutrients up from the ocean depths and swathing the coast in mist, is one of the richest parts of the planet, creating the world’s most productive marine ecosystem. It produces some 20% of the global human fish catch, and bird and other animal life abounds. In the 19th century, Pisagua supported a huge industry mining the seabird guano, and the birds remain. On the day we walked along the cliffs to Punta Pichalo, we watched thousands of Guanay and Red-legged Cormorants, Peruvian Pelicans and Brown Boobies streaming around the point and racing to intercept a vast school of small fish moving out to sea. The sheer numbers of birds and their desperate energy to be in on the feast were riveting.

  • In a small open boat bobbing in the swell just off the extraordinary sheer cliffs of Balls Pyramid, south of Lord Howe Island, a group watches entranced as Flesh-footed Shearwaters and White-bellied Storm Petrels come in to feed on berley (bait) thrown over the stern. The storm petrels, ‘Mother Carey’s chickens’ of sailor lore, are tiny and almost never seen from shore. They are pattering on the water surface in their characteristic way, holding their wings up to catch the wind and using their feet in the water to anchor themselves in place for a few seconds at a time (Withers 1979). It is enthralling to watch such behaviour that is normally inaccessible to land-based creatures.

  References

  BirdLife International (2016) Tribonyx mortierii. The IUCN Red List of Threatened Species 2016, .

  Boles WE (2005) A new flightless gallinule (Aves: Rallidae: Gallinula) from the Oligo-Miocene of Riversleigh, north-western Queensland, Australia. Records of the Australian Museum 57(2), 179–190. doi:10.3853/j.0067-1975.57.2005.1441

  Frith C (2013) The Woodhen: A Flightless Island Bird Defying Extinction. CSIRO Publishing, Melbourne.

  Gardner JL, Trueman JW, Ebert D, Joseph L, Magrath RD (2010) Phylogeny and evolution of the Meliphagoidea, the largest radiation of Australasian songbirds. Molecular Phylogenetics and Evolution 55(3), 1087–1102. doi:10.1016/j.ympev.2010.02.005

  Hilty S, Bonan A (2017) Tanagers (Thraupidae). In Handbook of the Birds of the World Alive. (Eds J del Hoyo, A Elliott, J Sargatal, DA Christie and E de Juana). Lynx Edicions, Barcelona, Spain, .

  Hutton I (1991) Birds of Lord Howe Island Past and Present. Ian Hutton, Coffs Harbour, New South Wales.

  Lamichhaney S, Berglund J, Sallmän Almén M, Maqboo K, Grabherr M, Martinez-Barrio A, et al. (2015) Evolution of Darwin’s finches and their beaks revealed by genome sequencing. Nature 518(7539), 371–375. doi:10.1038/nature14181

  Sato A, Tichy H, O’hUigin C, Grant PR, Grant BR, Klein J (2001) On the origin of Darwin’s finches. Molecular Biology and Evolution 18(3), 299–311. doi:10.1093/oxfordjournals.molbev.a003806

  Szabo JK, Khwaja N, Garnett ST, Butchart SHM (2012) Global patterns and drivers of avian extinctions at the species and subspecies level. PLoS One 7(10), e47080. doi:10.1371/journal.pone.0047080

  Weiner J (1994) The Beak of the Finch: A Story of Evolution in Our Time. Random House, London, UK.

  Withers PC (1979) Aerodynamics and hydrodynamics of the ‘hovering’ flight of Wilson’s Storm Petrel. The Journal of Experimental Biology 80, 83–91.

  4

  Mountains

  Torres del Paine NP: Andean Condors

  Not much could have distracted my enthralled gaze from the stunning panorama in front of me, but the huge black bird drifting between me and the view did it easily. I had wanted to see an Andean Condor since it featured in a book on animals that I’d absorbed and treasured as a small boy. An annoyingly precocious small boy, I must add (at least when it came to animals – in all else I was hopelessly shy and introverted). It is part of family lore that when my Glaswegian-born grandfather invited me to ‘look at the wee birdie’ in the book I politely corrected him with ‘actually Grandpa, it’s a Female Condor’ (I thought that ‘female’ was part of its name).

  The lookout at Lago Nordenskjöld in Torres del Paine National Park in Chilean Patagonia is one of my favourites in the world. It never ceases to astonish and delight me. You come on it after driving for some time through the park: a vast wind-pruned landscape where herds of Guanacos graze and skitter. Pull over, get out into the inevitable wind and gaze across the pale green ruffled waters of the lake to Los Cuernos – the Horns. (The milky blue-green water that characterises this part of the world is due to glacier-ground ‘rock flour’ in suspension.) Although the wind just ruffles the water on a good day, I’ve also seen the surface of the lake carried as a cloud of spray above the waves by wind that can knock the unwary off their feet. The Horns are truly spectacular: sheer pillars of granitic rock that rear up from the far lake shore. The lowest slopes are cloaked in tough Antarctic Beech (Nothofagus) forest but above that is bare cliff, a broad pale band above the dark base and capped with another hard dark layer (of basalt), with snow lying in gullies. Then gradually the scale sinks in. The peaks we’re looking at are more than 2 km above us: the apparent ‘snow faces’ at the end of the gullies are actually glacier walls more than 50 m high. The clarity of the air seriously messes with one’s perceptions.

  This is a vast landscape and it somehow seems appropriate that a bird that lays (disputed) claim to being the world’s largest flying bird finds its last stronghold here. It’s also a bird that can tell us lots of stories.

  Let’s start with the size, and it really is enormous! The male has a wingspan of up to 3.2 m, and weighs up to 15 kg; the female is somewhat smaller. It’s generally accepted that 15 kg is about the upper limit that a flying bird can be. True, there were pterosaurs and even birds heavier than that – the mighty Argentavis magnificens, which cast its shadow over the Argentinian plains 6 million years ago, weighed perhaps 70 kg – but these could neither have taken off nor stayed aloft by flapping (Ksepka 2014). They would have relied on either launching from a cliff or running downhill, and using air currents to stay up – they soared rather than flew.

  Featherless heads

  The mighty condors roost and breed on cliff faces and simply fall into space, after which they rarely need to flap, circling in the ever-busy air currents over the mountains. Not far from Nordenskjöld lookout, I once came across a remarkable sight: up to a dozen condors on the ground, feeding on the fresh carcase of a young Guanaco, or chulengo, perhaps killed by a Puma the previous night. One huge male exerted his dominance, lowering his great head to the ground, ruffling his white-collared neck and raising his wings to show his white secondary feathers and wing-coverts as a white panel against the black, and flushing his bare face a deeper red. Usually only one adult male is present at such a gathering and actual conflict is rare. Both sexes have featherless heads and necks, but the female’s is black and the male’s is red with a fleshy comb from eyes to bill, with wattles on his neck.

  Many birds have bare heads, for the same general reason – if you’re going to dip your head into something wet and sticky you don’t really want feathers to be all gummed up. This applies to various ibis and stork species that probe into mud, some friarbirds (large honeyeaters) that stick their heads into large nectar-rich flowers and both New World and Old World vultures, which get much of their intake from the interior of large carcases. But (have I mentioned there’s always a ‘but’?), it’s hard to explain the spectacularly bald heads and necks of wild turkeys, some guineafowl and the West African picathartes or rockfowl, for instance, as adaptations to feeding. Most of these do have colourful head and neck skin, which pl
ays a role in display, but it’s hard to say if this is sufficient to actually dispense with feathers, which can also be brightly coloured. One study on the Griffon Vulture of north Africa, the Middle East and central Asia concluded that its featherless head was related to temperature control (Ward et al. 2008), but it’s hard to imagine how this could be beneficial to the Andean Condor in the very chilly Andes and Patagonia. However, it could be if the function was later adapted to other purposes.

  How big can a bird be?

  A brief basic physics lesson, and trust me that it will be basic (Physics 1 was the only university subject I failed). As a bird gets ‘longer’, it also gets heavier, but at a much higher rate. A bird twice the length and wingspan of another has four times its surface area (i.e. it increases by the square of the length); this is a plus, because bigger wings mean more push. But it also has eight times its weight (which increases by the cube of the length). In other words, wing loading (weight per area of wing, which determines how hard it must work to fly) increases with size – despite larger wings, a larger bird must work twice as hard to take off as the smaller one half its size. A bird three times the size must work three times as hard, and so on. Take-off is aided by jumping and, in a larger bird, legs are as important as wings at the moment of take-off. But, jumping is much easier for a lighter animal: compare the relative heights that a flea, a frog, a wallaby, a horse and an elephant can jump. A large bird of prey such as a condor or a Wedge-tailed Eagle, especially if full of carrion, may have to run along the ground to take off; a swan or pelican or albatross must run along water.

  Taking off is the really hard bit, but it’s by no means the end of the problem. A large bird must also fly faster to stay up, so it must have relatively larger wings and flight muscles (as well as just proportionally larger), which in turn add extra weight. It’s a vicious circle that seems to vanish down its own plug hole at around 15 kg. You must then rely on soaring (once you’ve managed to get off the ground), but the heavier you are the faster you fall, so you must find stronger and stronger air currents to lean on. There are reports of rare individuals of very large birds such as Kori Bustards and Mute Swans that weigh 20 kg or more, but it’s not clear whether those atypical birds can still get off the ground.

  Another intriguing suggestion has been made about the upper limits to size, and it is independent of weight. All birds must regularly replace feathers, which quickly become worn and inefficient; this process is called moulting (more on this on pages 189–90). In 2009, Sievert Rohwer and colleagues at the University of Washington published a paper showing (very) mathematically that although feathers of larger birds must be longer than those of smaller ones – roughly double the length for a 10 times increase in mass – feather growth rates don’t increase accordingly (Rohwer et al. 2009). A point is reached at which the replacement feather can’t grow quickly enough to serve the bird’s purpose. For instance, a 10 kg bird needs 8 weeks to replace a single flight feather. With around 10 of the big primary flight feathers (though some larger birds have 12), it would clearly be impossible to moult them only one or two at a time. The options are to moult several at once, with the resultant extended disadvantage of inefficient flight for a long time, or to lose them all at once, meaning at least 2 months of being unable to fly, or to extend the moult over 2 or even 3 years. Many albatrosses take the latter option, but, even for them, the effort of breeding and moulting is too much in one year, and so they avoid breeding in consecutive years to focus on the moult (Langston and Rohwer 1996).

  A condor wishing to assert authority – like the big male at the chulengo – can, as noted, flush bright red to make his point. It was assumed that such displays were based on red pigments in the skin that evolved for the purpose, but Negro et al. (2006) showed otherwise for a diverse array of birds – in at least 20 Families across 12 Orders, most of which are large dark-coloured tropical species including cassowaries, vultures, caracaras, bustards and parrots. In many cases at least, the flushing is due to highly vascularised skin close to the surface, which originally developed to assist in heat loss; nearby skin under the feathers has no such characteristic. As species such as the condor came to use this feature also to signal information such as status and fitness, perhaps the value of this secondary use came to outweigh the disadvantage of an uninsulated head as some of the birds headed south.

  It is widely suggested too that exposing the skin to ultraviolet light and dryness helps control bacteria from the condor’s restaurants, but while highly plausible it’s hard to find evidence for this.

  The awesome alula: making flight possible

  As another condor landed hoping to get a share, she spread her huge wings and tail and feet to act as brakes, and raised a tuft of feathers on the angle of each wing. It would be easy to miss if I wasn’t watching her through my binoculars. This little tuft, the alula (AL-yoo-la), is arguably one of the most significant developments in the history of bird evolution.

  ‘Alula bird’

  Cuenca is an ancient walled city some 150 km from Madrid, with World Heritage classification. However, to a birder (not to mention a bird!) it has an even greater significance. From nearby, in the mid-1990s, a remarkable fossil was reported, of a superficially unremarkable bird about the size of a scrubwren. This bird, Eoalu-lavis, lived some 115 million years ago. The detail of the fossilisation makes me shake my head with wonderment at the sheer, beautiful unlikelihood of it. We know what it ate, because its stomach was still full of shrimps. And we know that it truly flew, as truly as any modern bird does, because its superb fossil feather impressions included an alula! (Sanz et al. 1996). For the record, Eoalulavis means ‘dawn alula bird’.

  But what is an alula and how does it work? As I have already confessed, I have no credentials at all in physics, and in any case even the professional aerodynamics people can’t seem to agree on the details of why a wing (be it of bird or aeroplane) actually works – at least as far as I can understand them. So, this explanation will of necessity again be simple. As the leading edge of a wing tilts further up (or if you’d rather, the ‘angle of attack’ increases), two key things happen. First, the lift increases (partly due to decreasing pressure on the top of the wing, as it forms a ‘pressure shadow’ behind the raised leading edge, so that the wing is forced up): this is essential if the bird is to accelerate and climb. However, the drag also increases as the area facing the wind does: this pulls the bird back, so it must flap harder to produce extra thrust to compensate. A wing held horizontal to the ground attracts least drag, but it will also not allow climbing so is of limited use.

  It is important to reduce turbulence over the leading edge of the wing, in part because turbulence breaks up the relative vacuum above the wing and increases drag. However, as the angle of attack increases, so does turbulence. This is manageable under most normal flying conditions, but there is one aspect of every flight where the angle of attack must be raised to almost 90°, with potentially disastrous results. This is at the moment of landing, where wings, tail and feet are spread fully out to deliberately increase drag, in order to decrease speed to stalling – just as I saw in the condor coming down hoping for a snack of chulengo. In such circumstances, turbulence over the wing would be catastrophic, simply dropping the bird out of the air with all the grace of their wingless reptilian forebears. But now the marvellous alula is spread, like a mini-wing stuck up from the real one (a perhaps unfortunate alternative name is ‘bastard wing’ – I find alula much more euphonious). Air flows through the slot formed and over the wing surface. For reasons well beyond me – and, I would tentatively and respectfully suggest, apparently beyond those much better credentialed than I, though it seems they’re getting closer – this air flow is nice and smooth and the bird, rather than stalling or crashing, touches lightly down (e.g. Lee 2015). (See Photo 30.)

  The alula is controlled by the first of the three remaining much-reduced ‘finger’ bones in a bird’s wing (but technically this is number two; one and five have
disappeared entirely). An aeroplane achieves the same thing by means of wing flaps and slots; the superb and sorely missed pteranodons did so by lowering a flap of skin across the front of the wing using a single small tiltable bone; bats use a network of tiny hairs across their wing surface to inform them of minute changes in air flow and prompt them to subtly alter the wing shape (Sterbing-D’Angelo et al. 2011). None could successfully fly without an alula-equivalent.

  Archaeopteryx apparently had not evolved an alula, so presumably hit the ground running, or crashing. It almost certainly couldn’t have landed on a branch from other than a short hop, or pounced onto prey, because it couldn’t have slowed its descent enough to do so. Somewhere in the brief few million years between Archaeopteryx and Eoalulavis the first alula appeared. No living birds descend from Eoalulavis, so either the alula evolved more than once or it arose very early in the story of birds, in a hitherto unrecognised species that was the common ancestor of every bird we see today. Either is possible, and either way it emphasises the critical importance of the alula in the long history of bird flight.

  Can birds smell?

  Unlike the much more widespread Turkey Vulture, the condors have no very useful sense of smell – they find their meals by sight, which is not so hard on the open country of the mountains. On the other hand, the Turkey Vulture might be better at finding carcases in general, but that alone isn’t enough – they need the massive condors to open a large carcase before the smaller birds can access it.