Birds in Their Habitats

by Ian Fraser

  Powder down is another pretty amazing feather type, present in a minority of bird Families, though these are as diverse as pigeons, parrots, cotingas, herons, frogmouths and the strange New Caledonian endemic Kagu. In parrots and pigeons, the powder down feathers grow in little thickets on different parts of the body, while in some other groups they are scattered throughout the plumage. These different patterns apparently reflect the fact that they evolved independently in different families. The feathers have tips that disintegrate into keratin powder, like talc (though not chemically), which either disperses through the feathers naturally or is spread with the bill tip. Either way, it apparently cleans, conditions and waterproofs the feathers (can’t you imagine the TV ad for its remarkable properties?). Another interesting characteristic of powder down feathers is that they are not moulted, but grow continually to replace the eroding tip (see Photo 29).

  Despite the lavish care given them, feathers inevitably deteriorate. They get worn by collisions with dust particles in flight, by the normal wear and tear of a vigorous life, by ultraviolet deterioration, by some bacteria that have evolved to digest feather protein and by the insidious feather lice. These are remarkable little animals that are among the ultimate specialists: not only is a feather louse likely to be limited to just one bird species, but to one section of its body.

  Moreover, a feather, like a hair or a fingernail, is dead, so once damaged it can’t repair itself (though hair or nail will continue to grow; a mature feather does not). The solution is moulting: the complete sequential replacement of all the feathers at least once a year.

  Moulting is a very tricky and potentially hazardous process: you can’t have gaps that leave you without proper body insulation or adequate flying abilities. Generally the process on one side of the body is mirrored on the other: for example, one feather on each wing, a small patch on each flank. The old feather is pushed out by the new, which grows from the same follicle. The process normally starts in autumn, when the most recent brood has been waved goodbye from the territory, or at least are finally looking after themselves. That very stressful period of feeding growing and demanding youngsters doesn’t need to be made more so by dealing with the handicap of incomplete plumage at the same time. It can take weeks, or even months, to complete the process, though some birds that have strategies to cope with a flightless period can speed it up. Many waterbirds, including ducks and swans and some seabirds, go to a nice safe quiet refuge, such as a lake or an island, shed all their flight feathers at once and are back to full flight capacity in 3 or 4 weeks time.

  Immature birds must moult into their adult finery, while those species in which the males (and, in a few instances, the females) stay incognito for much of the year but adopt colourful breeding attire,such as shorebirds, weavers and fairy-wrens, must moult their body feathers (though not those of wings and tails) twice a year. The Splendid Fairy-wren (now there’s an unhelpful name, among the galaxy of other splendid fairy-wrens!) that we’d admired further back along the road east of Hyden was just coming into his courtship glory. His head and neck were already flaunting a mix of patches of brilliant sky blue and deepest navy, but the rest of him was still drab winter brown with a scattering of blue feathers: presumably having a blue head is more important than the rest of him.

  And always, it seems, there are trade-offs to be made. If a bird finishes breeding late in the season – perhaps because it delayed starting until conditions were more conducive, or took a chance on a second clutch – it must hurry its moult to be at peak flying capacity and optimal insulation before winter strikes. However, it transpires that hurried feathers are not very good feathers. House Sparrows with accelerated moult, prompted by messing artificially with their day length, had shorter flight feathers with more ‘fault bars’ (weaknesses that can lead to breakages in barbules and even the main shaft) and body feathers with reduced insulating capacity (Vágási et al. 2012). If the birds were in poor condition to start with – perhaps after a difficult breeding season – the feathers were even less effective. The moral seems to be that if you’re not going to moult early, you’d better be in good condition; if not, you’re likely to find yourself in a nasty spiral that continues over coming seasons.

  But there was another attention-catching aspect of the running Emus too …

  A bird’s leg: a wonder of redesign

  An obvious thing when watching the elegant power of a running Emu is to make comparisons with human sprinting: not so much the elegance and power as the very basis of it – standing erect and using just two limbs for propulsion. But – yes, yet again that ‘but’…

  Something is very different: an Emu’s knee bends the ‘wrong’ way (well, wrong for a human leg at least). What on earth would have been the point of, at some stage of either our or their development, turning the leg completely back to front from its reptilian origins? Furthermore, it would have been the birds’ legs that were reversed, because a modern lizard’s leg still bends the same way that ours does.

  The answer is that it’s a trick question: a bird’s knee bends the same way that ours does, but we are not looking at the actual knee when we make the judgement. Over and over again, the answer to a puzzle about some aspect of a bird’s structure or behaviour comes back to necessary compromises to maximise flying efficiency, which in turn mostly comes down to weight minimisation. Not in this case, however –though not because the Emu gave up flying long ago, because those basics of anatomy go way back to its flying ancestors and are shared with all other birds (think of any other bird you like). No, the flight-related compromise in this case is driven by the great flight muscles that take up so much of the front part of the body. There is no room for the hips to be underneath the bird’s centre of gravity, and a bird doesn’t normally stand bolt upright but leans forwards, perhaps for reasons of vision and foraging and because of the attachment angles of the wings. The attachment point of the leg to the spine, the hip, is right at the back of the body from where gravity should cause the bird to fall flat on its beak.

  However, something very clever has happened in the past to compensate for this. The thigh, instead of projecting down from the body as ours does, is relatively short and runs forwards along the bird’s flanks; it is entirely covered by skin and feathers and anchored immovably in place by muscles against the side of the bird. We don’t see it at all in a living bird, but you only need to think of a roast chook to realise what I mean. When carving, the thigh must be cut out of the body.

  Now the thigh ends pretty much under the centre of gravity, so the leg may safely leave the body – but this joint (functionally a ‘hip’) is in fact the true knee, being at the end of the thigh bone. And this knee really does bend backwards, just as ours does! So the apparent ‘thigh’ of the bird leaving the body is in fact the true shin, and the apparently forward-directing ‘knee’ at the lower end of it is really the ankle … To make it even trickier (only for us, of course, this is not a problem for the bird) – the knee/‘hip’ and the true shin/‘thigh’ below it are often covered by feathers in all but the biggest birds, and are also often hidden by the wing.

  I hope you haven’t given up in exasperation by now, because I reckon this is really interesting. But you might instead have given up because I’m obviously talking nonsense – after all, below this ‘knee’ that I’m calling an ankle there is another section of leg that looks and functions for all the world as a shin. Fair enough too. However, this is another very clever evolutionary solution and we couldn’t be expected to recognise a piece of leg that we don’t need and for which we thus have no equivalent. It is comprised of a mix of extended ankle bones from above and foot bones from below, and it does just fine the job of keeping the bird at a sensible distance from the ground. Because most of the foot bones have been co-opted to make this new ‘shin’, birds have no choice but to (almost exclusively) walk – and run – on their toes.

  Meanwhile, the Emus have certainly had it away on their toes, so time for us to move on
too.

  Extinction

  The Regent Honeyeater is a truly, but oddly, lovely woodland bird. John Gould thought it ‘one of the most beautiful birds inhabiting Australia’ (Gould 1865). It has a black head and neck, with a strange warty bare patch around the eye, and the rest of the body is chequered and scaled in a complexity of black and yellow and white. It is also terrifyingly rare, seemingly fading out of existence before our eyes, even as lots of good people are working with increasing desperation to stop that happening – rather like watching a medical team fighting a steadily losing battle in the emergency department.

  I first saw a Regent in 1992: a pair of them busily gathering spider webs from the black deeply incised trunk of a woodland ironbark eucalypt at Wyangala Dam north of Canberra. Unfortunately, the group I was accompanying had very little interest and wandered off after a few seconds, but I was enthralled. I’ve seen them just three times since then, all in Canberra: a pair nesting in woodland at Mount Majura in 1994; then a decade-long hiatus until a single bird appeared not far from there on Mount Ainslie; and another single on the Australian

  National University campus in 2005. Not one since then. Unfortunately, the temperate grassy woodlands of south-eastern Australia in particular are among our most damaged and least protected habitats.

  Perhaps the worst part is that the Regent Honeyeater used to be not only common, but abundant, as revealed by accounts from around the turn of the 20th century: for example, it ‘moves about the country in flocks from 50 to 100 or more individuals’ (Australian Town and Country Journal 1896). In September of 1909, a report from Belltrees near Scone in the Hunter Valley claimed that, ‘ever since March last they have been with us in thousands’ (White 1909). And now? Probably less than 400 mature individuals in the whole world, and still decreasing, scattered ever so sparsely from eastern Victoria to northern New South Wales, though they once spread west to Adelaide and north into Queensland (Garnett et al. 2011; ANU 2016).

  I passionately want my pessimism over the Regent to be wrong: I shall genuinely grieve if it becomes the first mainland Australian bird species to become extinct in the wild in nearly 100 years. The last one was the Paradise Parrot of south-eastern Queensland in the 1920s and, if the Regent follows it, we can be reasonably sure it won’t be the last, especially among the woodland birds. The White Box-Yellow Box-Red Gum woodlands have been comprehensively destroyed for agriculture and urban development; one estimate is that less than 5% remain (ACT Government 2004). However, attempts to assess the remnants which are in anything like an original state are even more alarming -one well regarded study on the White Box woodland component concluded that only 0.1% of the original habitat survives substantially intact (Thiele and Prober 2000).

  But why the Regent in particular? Other woodland species are struggling, but probably none are in such a catastrophic situation. Sadly, we can’t really say definitively, though we understand various factors that, in combination, doubtless contribute. They seem to need particularly high-quality habitat, and wander the countryside apparently seeking areas of continuous high nectar flow. Sadly, the remaining woodland remnants mostly comprise lower quality patches unattractive for agriculture, and represent marginal Regent habitat. Some other large honeyeaters are more generalist in their requirements, and move into disturbed woodland. The closely related Red Wattlebird is larger and highly aggressive, and the slightly smaller Noisy and Yellow-throated Miners live in tough bullying xenophobic gangs. Gould made special mention of the Regents’ pugnacious disposition, but now they are overwhelmingly outnumbered wherever the living is good. And how do you help a species comprising just a few hundred birds that are constantly on the move over tens of thousands of square kilometres of countryside, and that can be absent for years at a time from a previously favoured locale? We don’t really know, other than via the current superhuman efforts at revegetating and monitoring. We still don’t know for sure why we managed to lose the Paradise Parrot and not others.

  It is perhaps fortunate that the approach to assisting more sedentary species is (at least theoretically) more straightforward. For woodland species, for instance, we need to understand the minimum requirements of the threatened species in terms of: the minimum size of a remnant vegetation patch; the maximum distance to the next patch; key tree, shrub and herb species; the nature of the understorey; the age of the trees; and so on. Often it is possible then to identify an ‘indicator’ or ‘umbrella’ species whose requirements are such that providing them will automatically protect other species. A useful definition is ‘a species whose presence indicates the presence of a set of other species and whose absence indicates the lack of that entire set of species’ (Lindenmayer et al. 2000). Sometimes a large predator (e.g. a Jaguar or large forest eagle in South American rainforests) is cast in that role, though this is not likely in an Australian woodland. However, in the south-eastern Australian woodlands, both Brown Treecreepers and Hooded Robins are reliable indicator species – if they are present, all other threatened woodland birds are also likely to be. Unfortunately, Regent Honeyeaters don’t fit this model.

  Extinction, like evolution, is not an event (other than for vanishingly rare broad-scale accidents such as meteorite strikes) but a process. I was once taken publicly to task by a journalist who objected to my use of ‘extinction’ to describe the loss of Brolgas from the Canberra region – ‘radically devaluing’ the word was the accusation. He insisted that it could only be used for the final and total loss of a species and that its use for anything less would alarm people to the point that they wouldn’t be appropriately alarmed when something worse came along. He climaxed by accusing me of ‘humpty-dumptying’. It was a nice insult, but I believed it was misapplied. We may choose to define extinction as the moment that the last individual disappears – and for a few species where the last individual was known to be in a zoo (the Passenger Pigeon and Thylacine spring accusingly to mind) we can indeed precisely log the dismal moment. If, however, we reserve use of the word only to report that the organism has gone forever, that seems to me to be a hollow, and perhaps even amoral, usage. We really do need to be alarmed, and to respond accordingly, well before that happens.

  I think of all the populations that comprise a species as being like little lights across the countryside. Extinction begins when those little lights start to flicker and go out until finally – total darkness. We should see the spreading tenebrous patches as our alarm call, rather than regard the remaining lights as reason for complacency.

  There are other aspects too. Although ultimately the survival of the species is paramount, its disappearance from areas where it used to live is cause for genuine sorrow, as well as concern for the broader implications. The plains around Canberra supported flocks of Emus, Brolgas and Australian Bustards. The woodlands rang at night with the thrilling wailing choruses of Bush Stone-curlews: I have a friend who remembers them calling in northern Canberra in the 1950s. No more though. The last three species named can no longer be found in any numbers within many hundreds of kilometres of Canberra, though they are still quite common in the tropics. Does that make it acceptable though?

  Another serious problem is that we are still unravelling bird taxonomy all over the world. In Australia, over the last decade or so, around 16 new species have been recognised (nearly all passerines), mostly unanimously among taxonomists, through examination of separate populations previously assumed to have belonged to one species. These include three new species of quail-thrush (nearly doubling the number), and Western Australian populations of common eastern states species the White-naped Honeyeater and Golden Whistler (e.g. Dolman and Joseph 2015). What if some of those populations had been allowed to slip into oblivion under the assumption that the ‘species’ was doing well enough elsewhere?

  Often the cause of extinction is clear enough. On the Limestone Plains (where Canberra now stands), the Emus and Australian Bustards were hunted to extinction. The Brolgas were shot too, but drainage of wetlands was probabl
y a more profound issue. The stone-curlews were eaten by foxes, in addition to the loss of woodlands. Rarely, however, has the cause been so explicitly tied to a single incident as the shipwreck of the Makambo off Lord Howe Island, which introduced rats to the island (page 66), or to the moment when the Duke of York stuck Huia feathers into his hatband.

  The Huia was a remarkable bird; indeed all birds are, but this one really was special, and of great spiritual significance to the Maori. It belonged to a small New Zealand endemic Family called the New Zealand wattlebirds (no relation to the Australian honeyeaters of the same name). It was a big darkly iridescent bird of the deep wet forests, with broad white tail tip and large red face wattles. But the bill! Or rather bills, because those of male and female were quite different. His was heavy and crow-like, as the descriptions put it; hers was long, slender and deeply decurved. It seems they worked together, he breaking open the surface of rotting logs, and she probing deeply into the loose material to extract big juicy grubs. Well, that’s one story anyway, though, like so much else about the Huia, it’s hard to be certain. Perhaps they simply focussed on different foods, including fruits, to enable them to live in a smaller territory.

  Living in old growth forests on the North Island, they suffered from habitat loss from the time the Maori arrived, but things got a lot worse in the 19th century as vast swathes of forests were turned to farmland. The Maori hunted Huias for feathers, but only very senior people could wear them and there were firm restrictions on when they could be taken. European settlers, however, slaughtered them to sell to private collectors and museums back in Europe. Nonetheless, by the end of the 19th century, the bird survived in mountain forests and it is possible that the new conservation laws would have in time been better enforced than they were (essentially they were blatantly ignored).