Birds in Their Habitats

by Ian Fraser

  The remarkable precocity of Hoatzin chicks, plus the unique possession of sharp claws on fingers two and three, has often induced speculation about direct links to dinosaurs, and specifically to Archaeopteryx, which is widely posited as the ancestral bird and which had three such wing claws. However, they have had plenty of time to come up with their own solutions to problems. Adult Hoatzins are big enough to be safe from most predators, but the chicks are not. Instead, even at just 3 days old they simply tumble into the water when threatened. Moreover, they dive and swim, kicking and moving their wings for propulsion. When they feel safe again, they scramble back into the trees, hauling themselves up with the claws, with neck, feet and beak. This is amazing behaviour for such young chicks.

  Let me try to paint a Hoatzin for you (you could, of course, just go and look it up, but for now I would rather you kept reading). It is dark brown above with white bands across the wings and white streaks up the neck. There is a broad creamy band across the tip of the tail, and a rich chestnut panel in the wings (and on the flanks and lower belly, but you only see them when the wings are up). Then there is the head … a long spiky ginger crest that looks like a heavily gelled mohawk is perched above a bare blue face and dark red eyes. They are thus large and conspicuous, and are always along the edges of rivers and lakes, but often the first indication of their presence, as at Cocha Salvador, is a low cacophony of asthmatic huffing and hissing, with a miscellany of honks and hollow grunts. With this to guide the eye, we become aware of up to a dozen or more of the huge birds perched, albeit somewhat precariously, in groups on branches above the water. The problem is that they don’t move much: they spend much of their day loafing.

  Needless to say, there is a very good reason for this, and it is to be found in their diet. Hoatzins are most unusual among birds in being primarily leaf-eaters. This raises a very interesting question: vast numbers of mammals (and an even vaster biomass of them) are leaf specialists, relying on millions of tonnes of leaves (especially grass leaves), most of them eating nothing else from weaning to death. By contrast, hardly any birds do so; only some 3% of bird species, from only 14 Families of some 230 extant ones, eat leaves as a regular part of the diet. Why is this?

  Birds eating their greens

  A clue to these low numbers is in the additional observation that the majority of leaf-eating birds are larger terrestrial species – in addition to the Hoatzin, geese and ratites (emus, ostriches, rheas, etc.) are good examples. There are two problems with leaves as food. First, unless you’re eating out for pleasure, the basic purpose of food is to obtain energy, and quite frankly leaves are a lousy source of energy. By weight, leaves only give half the return of fruit and a quarter that of insects and other wriggling goodies. Further, to get even that much return requires a veritable internal factory, run by a huge team of skilled and highly trained bacteria – no other creature (except for a few clever silverfish) can break down the complex sugars of cellulose, which form the fibrous mass of leaves. Grazing and browsing mammals have big fermentation chambers wherein the bacterial workforce does the job of digesting the cellulose. It is not a rapid process though – a Koala’s gut can take up to 8 days to break down a eucalypt leaf, so a large caecum is required. In the Koala’s case it is 2 m long and 10 cm in diameter: definitely not the sort of accoutrement you want to carry around with a strict baggage weight limit for your flight (in fact, as we will see, it effectively precludes a bird that uses this strategy from flying).

  Foregut fermentation is a common mammal strategy, but the only confirmed avian example of it is in – yes – the Hoatzin. I guess that 64 million years of isolation is enough uninterrupted time to evolve a system that no other bird has managed. However, it takes 24 h to digest its salad, and at any given moment a Hoatzin is carrying something like 25% of its bodyweight in the form of digesting leaves in the foregut. There is another problem associated with this too: the foregut takes up so much room that the Hoatzin has had to largely do away with the sternum (the keel, as seen in a chook on a plate). This is the anchor point for the great flight muscles. As a consequence, a Hoatzin can barely fly, and in practice it mostly just scrambles through branches and glides.

  Hoatzin chicks are fed by regurgitation on a soup of fermented foliage – not for them the protein that the young of most vegetarian birds are given to provide them with an early boost. There is one other apparent spin-off from this unusual digestive system too. In at least some parts of its range, the Hoatzin is regarded as smelling (like cow dung according to some reports) and tasting bad. In Guyana it is known as ‘stinking pheasant’, and ‘stinkbird’ and ‘stinky turkey’ are often cited as names elsewhere. It appears that this view is not universal, but, even in places where a revulsion to the bird is not reported, it seems to be eaten rarely, which would be unusual for such a large and easily procured bird. It may be that they are always unpalatable (or just smelly), but that additionally in some areas they eat toxic leaves. There are suggestions that Hoatzins may possess natural detoxifying chemicals, which are currently unidentified (Thomas and Bonan 2017).

  But what about the other birds that do eat leaves? After all, 3% of 10 000 species is still some 300 species. To get a reward from your leafy lunch you don’t actually have to go to all that fermentation trouble – by just grinding leaves up you can get to digest the cell contents without bothering about the nasty fibrous stuff, and that’s exactly what all other leaf-eating birds do. However, this means that you are getting even less of the potential value of the salad, so you must eat more and have a bigger storage space, which means having a bigger body and/or a reduced flying capacity. There are very few small flying leaf-eaters. These include some of the saltators (South American tanagers – or possibly cardinals, but let’s not get distracted now), the three South American plantcutters (cotingas) and the African mousebirds (small non-passerines). I’ve had the fortune to see all three groups in the wild, and although the mousebirds are certainly flutter-gliders, the other two are actually perfectly respectable flyers. This is a reminder, incidentally, that nature rarely feels constrained by the rules we write for her (they are usually our rules, rather than hers). The Rufous-tailed Plantcutter, found as far south as the stormy shores of the Strait of Magellan, is perhaps the smallest leaf-eating bird, relying almost solely on leaves in autumn and winter when fruits are scarce. The preference of all of these leaf-eaters is for the youngest, most tender shoots.

  In Australia, the bowerbirds are among the few leaf-eaters, as any gardener in their territory will know. The most dependent on leaves is the Tooth-billed Bowerbird of the Wet Tropics of Queensland. It, like the plantcutters and the Satin Bowerbird, turns to leaves mostly in winter when there is a dearth of the preferred fruits.

  The other problem with leaves is that so many of them are downright dangerous to eat. Plants have had hundreds of millions of years to build their defences against those billions of creatures – mostly insects – which would rudely chew them. There are more than 30 000 identified chemicals found in plants whose use is not apparently related to daily functioning: many of these are probably involved with defence. Many of the chemicals whose function we do know are pretty scary. Some wattles have cyanide precursors: break the leaf, bring the chemicals together, and you get a very nasty mouthful indeed. Milkweeds have cardiac glycosides, which are very unpleasant heart poisons. All in all there are very good reasons to look for other food sources, no matter how tempting and abundant leaves may be.

  Fascinating as these very singular Cocha Salvador birds undoubtedly are, there was another species present which I was also very pleased to see.

  Muscovy Ducks, and birds in service

  In the shadows near the bank, two near-black ducks with a greenish sheen glided cautiously. The male was larger, with a white wing patch and big fleshy red growths at the top of his bill, which was banded black and yellow. Though I’d never before seen them in the wild, I was familiar enough with Muscovy Ducks, though the domestic ones I knew were m
ostly white. They were common domestic birds in South America when the conquistadors came with swords, cannon, bible and a rapaciously brutal certainty of their own rightness and superiority. Without written records (the South American cultures had sophisticated craftspeople and engineers, but seem not to have developed written language), we cannot know how long they had been commensals by then. However, given the long history of sophisticated farming practices and domestication by the Incas (and all the cultures that came before them), there is no reason to suppose that it was a recent event. There is some archaeological evidence for domestication by the Mochica people of southern Peru nearly 2000 years ago, though that wasn’t necessarily the start of it either (Stahl 2005). Muscovies are still common as domestic birds in South America, especially in rural villages, but in the wild they are now uncommon throughout most of their extensive range and, very sensibly, mostly very wary of humans.

  Muscovy Ducks arrived in Europe with returning Spanish looters in the 16th century. There is a great deal of confusion about the origin of their English name, and considerable intellectual gymnastics have been performed in an attempt to justify their connection with Moscow, but all such efforts seem doomed to failure. The reference was apparently to ‘musky’, in relation to a supposed characteristic of their flesh. The great 17th-century philosopher, scientist and theologian, the ‘father of British natural history’, John Ray, was quite unequivocal on the matter, and I think his proximity to the problem should be respected.

  Regardless of this, these New World ducks were relative newcomers in a hemisphere where ducks had been part of daily human lives for at least 1500 years. The ancestor here and in Asia was the familiar ‘Wild Duck’ of Europe and Asia (and North America), the Mallard. However, the actual origin of duck domestication is mysterious, and seems not to have pre-dated the Romans in Europe at least (e.g. Albarella 2005). It is suggested that duck domestication in Asia preceded this, based it appears largely on the number of breeds present now, but direct evidence seems to be lacking. It would not have been a difficult process – ducklings from clutches of eggs taken from the wild and hatched under domestic hens would imprint on humans if they were present when the ducklings emerged.

  Geese, however, seem to have been part of human lives for longer than that. Egyptian Geese were domesticated by the Old Kingdom of Egypt, which ended some 4300 years ago. Curiously, they were apparently (albeit inadvertently) ‘liberated’ by the Persians 2500 years ago when they conquered Egypt. Neither Persia nor subsequent Egyptian cultures renewed the relationship. European domestic geese derive from wild Greylag Geese: the oldest direct evidence is in the Odyssey (i.e. 2800 years ago), but there is a belief that the association is much older (e.g. Albarella 2005). Perhaps the most famous geese in our culture are the ones that supposedly guarded Rome. Actually it is not at all certain that they did, but the legend has it that a flock of domestic geese alerted the apparently dozy guards to the approach of the Gauls 2400 years ago; whether they were already sacred to the Temple of Juno, as reported, or were subsequently promoted, isn’t clear. There is no doubt though that they are eminently suited to the role, being nosy, noisy, aggressive insomniacs. There are lots of stories of ‘guard geese’ since then, including in modern times in prisons in Colombia and Brazil, on South Vietnamese airbases in the 1950s, a whisky distillery in Scotland (until as recently as 2013), police stations in China and US military bases in Germany. Before we move on from European domestic geese, I do love the image of flocks of geese being ‘shod’ by walking them through tar and sand to protect their feet before walking them in large numbers and over considerable distances into town to be sold at markets (Carboneras 2017).

  In China, Swan Geese were also domesticated millennia ago, though again the evidence for the timing is scant. One problem is that, where hearth bones are relied on as evidence, it is nearly impossible to distinguish between wild and domestic birds. Even in art, and where captive birds are depicted, it is very hard to say if they are domestic or newly captured wild stock.

  Probably the most familiar poultry are domestic fowl (I actually think of them as ‘chooks’, but that’s probably a bit too Australia-centric to use exclusively here, and I’m afraid that to me ‘chicken’ still implies a yellow baby chook). Although the Green Junglefowl of Java and nearby islands, and the Grey Junglefowl of India, were undoubtedly domesticated by people a long time ago, and have probably donated genes to modern farmyards and backyards, it seems almost certain that the Red Junglefowl is the major ancestor, brought into domesticity by the great civilisations of the Indus Valley in India 4000–5000 years ago. (These cultures also brought sheep, elephants, buffaloes, goats, cattle and camels into the fold.) From here they spread with traders, reaching north-western Europe, Egypt and China by 3500 years ago. They were widespread throughout the south Pacific before Europeans got there. On many of these islands, runaways have reverted to the wild, and to the physical characteristics of their distant Indian ancestors. It was only to reach the Americas and (apparently) Australia that chooks required European assistance (McGowan and Bonan 2017).

  There is archaeological evidence that Native North Americans have been domesticating Wild Turkeys for perhaps 2500 years. Cortés brought Aztec-domesticated Mexican turkeys back to Spain in 1519. The origin of the name ‘turkey’ is convoluted to the point of surrealism. According to one story, Helmeted Guineafowl were apparently taken from Africa to Turkey, perhaps via Portugal, in the 16th century. They had been kept as domestic birds in Egypt at least 4500 years ago, and in the eastern Mediterranean from around 2500 years ago, but disappeared from Europe with the fall of the Roman Empire. From Turkey they reached Europe and became known as Turkey-cock and -hen or simply Turkey (or Turky). However, it is also quite possible that ‘turkey’ was just a reference to ‘somewhere foreign and distant’ and that the country was never involved! Either way, when ‘real’ turkeys arrived a little later, the two birds became conflated (or were regarded as variants of the same bird) in the public mind. When this mental mist cleared, ‘turkey’ had become applied to the American birds, and ‘guineafowl’ to the west African birds (Porter 2017; Fraser and Gray 2013).

  Venerable as is the history of these (conscripted) human companions, none of them are the longest standing of our feathered domestics. Rock Doves were first domesticated by grain farmers (who were involuntarily already feeding them), as mentioned in Mesopotamian records from more than 5000 years ago, though some believe that it could have happened as long ago as 10 000 years (Johnston and Janiga 1995). While we mostly think of domestic pigeons now in terms of racing and shows, at that stage, as with all the other domestic birds we’ve discussed, the original interest was in their culinary properties. However, pigeons have been used to carry messages since King Cyrus of Persia did so 2500 years ago, and continued to be used by the military well into the later 20th century (Westfahl 2015).

  Their edibility has overwhelmingly been the primary focus of our interest in domesticating birds, but is not the only one. The imprisonment of small birds and parrots for human gratification is widespread and long-established – parrots have been caged for many centuries from India to Mexico. Today the most common cage birds in western culture are, to my great sadness, two arid-land Australian parrots: Budgerigars and Cockatiels. Both are essentially flock birds and (to borrow from a Jane Goodall quote about chimpanzees) one budgie is no budgie at all. The trade in small caged birds for household pleasure is enormous in South-East Asia; in Indonesia in particular a widespread and open illegal trade is driving species such as the Black-winged Myna to extinction (TRAFFIC 2015).

  Atlantic Canaries were brought to Europe from the Canary Islands (named for dogs, not birds, but let’s not get distracted) soon after 1400 and soon took over as the most-popular cage bird from European Goldfinches. They came down to earth abruptly when taken down coal mines to warn miners of gas infiltration (by dying) and they played this role in Britain until the late 20th century.

  King Quail were r
eputedly used as hand warmers by Chinese emperors 5000 years ago. And, just to return to wetlands where this topic started, the continued use of Great Cormorants in China (for 2000 years) and Japan (for 1500 years) to fish for their controllers (albeit mostly now for tourists in Japan) is well known. Perhaps less-known, however, is the traditional use of Oriental Darters for the same purpose in South-East Asia and north-east India. Moreover, this practice (regarding cormorants) wasn’t always exclusively an eastern pursuit. Members of the British royal court of James I delighted in the pastime for a while from the early 17th century. It ebbed and flowed in western Europe over subsequent centuries, but always as an upper-class pursuit, as opposed to its practical purposes in the east. There was a revival in England and France in the 19th century. Its derivation in Europe seems to have been independent of that in Asia, and the use of neck rings to prevent the birds from swallowing the fish seems not to have been adopted in Europe (Beike 2012).

  Jerrabomberra Wetlands, Canberra

  Just 3.5 km from the national parliament, and less than 5 km from the city centre, is an oasis of wetlands, creeks, native plantings and rough grassy paddocks where I have seen over 120 species of birds. Like Gum Swamp, it is a blend of natural and artificial. From a nearby hill, we can see it as a series of channels, seemingly artificial, across the open ground. In fact they are palaeochannels of the Molonglo River, gouged out in past big floods, and left behind when the river later returned to its own, or a new, channel. In pre-European times, they would have filled in wet years, then dried when El Niño returned. Now the flat shallow expanse of Kellys Swamp is kept watered in all but extreme drought conditions, as just downstream the Molonglo is backed up by Scrivener Dam to form Lake Burley Griffin, the centre point of the national capital. I have spent uncountable hours over the years – alone or in company, in good times and (occasionally) in bad – in the bird hides watching the ever-changing parade.