Birds in Their Habitats

by Ian Fraser

  The Silver Gull is one of the world’s smaller gulls, an abundant bird around the coast of Australia and well inland, even breeding on the desert salt lakes in the very centre of the continent on the rare occasions that they flood. In this situation, they prey on the eggs and chicks of other breeding birds, to the extent that control programs have been instituted on occasions to protect the rarer species. Silver Gulls have adapted with enthusiasm to human habitation, gathering in flocks at rubbish dumps and anywhere that food scraps are available. Opening a parcel of fish and chips at the beach can be a hazardous undertaking, as one is inevitably and instantly surrounded by dozens of shrilly demanding gulls. Sadly, I suspect that many people believe that chips are in fact their natural food. And the gulls roost on open areas for safety, including under lights in order to see approaching predators – this predilection certainly includes cricket grounds and, as a result, they may be one of the most incidentally televised birds in the world.

  Back at the G, as the ground is universally known here, the bird eventually staggered groggily to its feet to the astonished delight of the crowd, which rose in a standing ovation. It stood gasping for a while – then to the acclaim of the world (this story really was reported across much of the globe) flew unsteadily right back to where it had been previously stationed. (Some outlets claimed the bird was attacking its former rescuer – presumably for his shooting gesture – but a quick scrutiny of the footage makes it clear that this was not part of its plan.)

  When birds collide

  Some years ago I was given a delightful 1953 book called Murray Walkabout by Archer Russell. In it he recounts an apparently very tall story wherein he describes a Sacred Kingfisher killing a Grey Teal. ‘Straight as a javelin it flew, straight into the middle of the covey it flashed. As the kingfisher flew among them, the teal rose in their flight and then sped on – all but one. That one first swooped and then fell headlong into the water … The kingfisher had struck the teal on the head, apparently piercing the brain and killing the bird instantly’ (Russell 1953, p. 27). He makes it that clear he regarded it as an intentional attack. It has worried me since I read it, because it seems to be such far-fetched nonsense in the context of an otherwise generally sensible and credible book. However, it recently occurred to me that perhaps he really had simply observed a remarkably unlikely accidental collision and misinterpreted it.

  And while this event, if it happened thus, is anything but normal, such unfortunate conjunctions of time and place involving birds happen all the time, not least on roads. I’ve had the misfortune to hit more birds than I want to think about in the course of driving hundreds of thousands of kilometres around Australia, but one bizarre event sticks in my mind. I was driving early one morning through the vast wild expanse of the inland Pilliga forests: 100 km of mesmerisingly beautiful ironbark and box eucalypts and cypress pine. I winced as a Laughing Kookaburra flashed across in front of the car, relaxed, then watched in horrified fascination as it swung high into the air, turned back and homed in with what seemed like determined inevitability on the windscreen. Out of the whole vast grey-green expanse of the Pilliga, that windscreen was a pretty tiny dot at that precise moment in time, but it and bird coincided, to the disbenefit of both. And why not? I know of smaller objects and smaller birds doing so, no matter how improbably.

  In the Marylebone Cricket Club museum at Lords in London is a House Sparrow mounted on the cricket ball that prematurely ended its career in 1936, when it flew across the pitch during an MCC v. Cambridge University match, a moment after Jehangir Khan had released the ball. Tom Pierce, the batsman, was left waiting for the ball, which never arrived. (Jehangir’s son, Majid, went on to captain Pakistan, but never matched his father’s achievement.)

  I don’t want you to think that I’m cricket-obsessed, but I know of at least one other bird that died in mid-pitch, this one an even nippier Welcome Swallow at the Adelaide Oval in 1969. Greg Chappell, then a young bloke, was bowling to John Inverarity, at that stage still representing Western Australia. The ball suddenly dipped alarmingly and bowled the perplexed Inverarity. When he was half-way off the ground the honourable South Australian fielders called the umpire’s attention to the dead bird lying some distance behind the wicket, and Inverarity got called back. It beats me how no-one saw the bird being hit, but there you go. I also wonder if the fielders would have mentioned it these days.

  I am reminded too of another ex-sparrow whose much more recent demise was premeditated. It was shot in 2005 in the Netherlands – presumably after a fair trial and all appeals had been exhausted – for slipping through an open window and pre-empting the felling of 23 000 dominos, just before the lucrative television coverage to 11 countries began. But that is irrelevant to this story.

  Inspired by these unlikely events, I went looking for others, and in the process found myself straying into the strange parallel universe of YouTube. (And in case you think I am being a little unkind to that monumental institution, consider that some of the following incidents, involving the sudden violent death of unsuspecting birds, are filed under Comedy.) A left-handed baseball pitcher hurls the ball – and a bird taking a short cut (either gull or pigeon I think) explodes in a cloud of feathers. The snout of one of a group of performing dolphins leaping out of a pool clips a passing gull, which cartwheels into the water. In a doubles tennis match, a small passerine (possibly a swallow) swoops across the net: ball and bird stop dead in their respective tracks. In Buenos Aires, a shot on goal by a soccer player results in a dead pigeon.

  Birdies inevitably feature in golf. A woman – possibly a touch more amateur than some of the previously mentioned (human) participants – tees off and, unfortunately for the gull foraging some 15 m ahead, the golf ball doesn’t get above ground level. On the other hand, professional golfer Tripp Isenhour was charged and sentenced in 2007 for deliberately killing a Red-shouldered Hawk with a golf ball, to punish it for making a noise and interrupting something vital, but unspecified, which he was being filmed doing.

  At the other end of the scale, a space shuttle rocket, weighing apparently some 2000 tonnes, clips an unidentifiable (but presumably large) bird with the cone. It appears to not be moving very fast, but the inertia is irresistible. And perhaps with that it is time to change the direction of this narrative …

  Canberra yet again: hybrid parrots

  In the leafy backyard I mentioned earlier, I put out seed for parrots a couple of times a week. Over the course of a year I could expect up to seven parrot species to drop in, while a couple more just passed over. One pair of visitors I found particularly intriguing. One was a Crimson Rosella, the commonest parrot visitor; the other, however, was a young bird, and clearly a hybrid with an Eastern Rosella. The Australian Capital Territory is an interesting area biologically, in that here three major habitat types come together. The high subalpine woodlands and alpine heaths of the Australian Alps reach their northern extent, the wet montane forests of the coastal hinterland are close to their most inland limits and the great grassy woodlands of the western slopes of the Great Dividing Range sweep down from the north and west. Generally, Eastern Rosellas are woodland birds and Crimsons are dwellers of the mountain forests, so the situation in Canberra where they live side by side is actually an unusual (though not unique) one. Before the coming of a city, they probably very rarely saw each other, with the Easterns staying out on the plains and the Crimsons in the mountain and hill forests, but gardens and parks provide elements of both those habitats so they have become neighbours, of us and of each other.

  Becoming a species: it doesn’t happen overnight!

  For those imbued with the axiom that species represent populations that are unable to interbreed, the existence of such a hybrid is a challenge – but it ought not to be. Speciation, whereby isolated populations of a species develop in different directions from those taken by their now distant relatives, to the point that they can’t interbreed if and when they do come back into contact, is best thought of as a
process rather than an event. Let’s call the ancestor of the closely related Flame and Scarlet Robins, relatively common and familiar birds in south-eastern Australia, a Flarlet Robin. When something intervened – most likely changing climate associated with the glaciation cycle of the current ice age – pushing different Flarlet Robin populations into different habitats, it was just the start of a steady journey towards eventual species-hood. Each population was facing different challenges, different climates, plants, prey and predators. Adapting to all these, plus more or less random genetic variation, drove changes that were ultimately critical. We can imagine the start of the journey, and we can see the end-point (at least so far), where Flame and Scarlet Robins can and do live side by side but never interbreed. However, there was not a moment when a Flarlet Robin went to sleep and awoke as a Scarlet Robin, nor did a Flarlet Robin lay eggs which hatched into Flame Robin chicks.

  We don’t have a problem with such a concept in other day-to-day processes. If we choose to grow our hair long (and I refuse to believe that anyone of my generation didn’t at some stage – actually no, to be fair, I don’t ever recall a male engineering student doing so), we don’t expect suddenly to be able to say ‘aha, now it’s stopped being short and is long!’. If I were to let a glass of beer sit untouched – well OK, that’s pretty implausible, let’s make it a sparkling water – I wouldn’t be able to sit and observe it, saying ‘sparkling … sparkling … sparkling … now, it’s flat!’. We define the beginning and end points and accept that there’s a continuum in between them.

  But in other matters we have an obsession with being able to pigeonhole and label things precisely, which makes it very hard for us to understand the process of evolution. We are lucky in that the intermediate stages of the journeys from Flarlet Robin to Scarlet and Flame Robins are all dead and lost to us. If we could see the long, long chains of individuals, each externally indistinguishable from its parents and its chicks, our frazzled minds might be forced to concede that Scarlet and Flame Robins can’t, so don’t, really exist! (For a much more detailed and erudite discussion of this, I don’t think we can go past Richard Dawkins’ story The Salamander’s Tale in his marvellous The Ancestor’s Tale; Dawkins 2005).

  Life is like an old-fashioned movie, comprising vast numbers of individual snapshots strung together; it is by merest chance that we are now in this frame, and not any of the thousands of other possible ones that precede and follow this one. And in this frame Flame and Scarlet Robins were separated for long enough that the journey to species-hood is completed, and they can never produce joint young again. They don’t recognise each other as potential mates, and their internal chemistry would almost certainly prevent successful fertilisation even if such interaction were to occur.

  For the rosellas, however, in this frame that journey is not quite so advanced: they don’t generally interact and, when they do, as in Canberra, they still nearly always maintain their individuality. Occasionally, however, something goes wrong: perhaps they are young inexperienced birds, maybe they lost their parents early, perhaps some had even escaped from aviaries where they never learnt how to be an Eastern or Crimson Rosella. In such unions, we would expect the offspring to be infertile, but again it is a matter of timing in the speciation journey, and I have seen some circumstantial evidence that my backyard hybrid may have bred, but the line apparently eventually died out and there is no evidence of a spreading pool of rosella hybrids in Canberra.

  But what about those birds that in this frame are not nearly so far down the speciation track? Australian Magpies (named for their superficial similarity to the Northern Hemisphere magpies, which are crows, to which our magpies are not related) are found right across the continent. There are eight Australian subspecies recognised (plus one in New Guinea), which fall into three well-defined groups, which used to be regarded as separate species. The White-backed Magpie of near-coastal south-eastern Australia and the Black-backed of most of the rest of the country are readily distinguished, as the names imply. The male of the Western Magpie of the south-west of Western Australia is identical to the White-backed, while the female has an attractive black back with white-edged feathers.

  It has been suggested that in the glaciation before last (i.e. around 100 000 years ago) Black-backed Magpies entered Tasmania when the floor of Bass Strait was exposed as the Bassian Plain, and were trapped there when the ice caps melted and the seas rose again. In the 70 000 or so years until the next glaciation and drop in sea level, a mutation for a white back appeared and became ubiquitous in Tasmania; it seems that the genetic difference between the two forms is very minor indeed. At the time of the most recent glaciation (roughly 20 000–25 000 years ago), these new White-backed Magpies invaded the mainland and began to push north and west along the coast, rolling back the Black-backs (Burton and Martin 1976). This is not confirmed: Mitterdorfer, working with a limited number of genetic markers, suggested that the mainland White-backs are actually more closely related to the Black-backs than they are to the Tasmanian birds, which implies that a different, older event separated mainland ancestors of Black- and White-backed Magpies (Mitterdorfer 1996). The Tasmanian origin appeals (offering an easily envisaged narrative), but that doesn’t make it right and we’ll have to wait a bit longer for the definitive answer.

  All magpie subspecies readily interbreed where they overlap. Canberra happens to be in the zone of hybridisation of Black-backed and White-backed Magpies, so that, although Black-backed is the dominant form in most of our yards, White-backeds are not uncommon. Where they interbreed, their chicks exhibit a full range of back colour from all white to all black (i.e. different proportions of each; they don’t blend to become grey). This hybridisation zone is roughly 120 km wide, and on the east coast it is moving steadily north. In the past 30 years, I’ve seen it move from the far south of the Australian Capital Territory north to near Canberra. In the light of our earlier discussion about climate change, it might be beguiling to attribute this movement too to global warming, but there is no evidence that there is any climatic advantage to being either black-backed or white-backed. It seems that the more prosaic explanation is the correct one: White-backs are simply a little larger, and are slowly pushing the Black-backs north.

  An intriguing aspect of this hybrid zone is its stability, rolling slowly north but not expanding into an ever-widening blur of hybrids. It seems that magpie behaviour is the explanation for this: non-migrants, they are strongly territorial breeders that cling fiercely to their territory, and even birds that haven’t yet attained territorial status just hang around on the fringes awaiting their chances.

  Given the existence of eight abutting subspecies, clearly magpie populations have been separated many times in the past, altered to some extent (and in the case of back colour, quite strikingly) but have always come back together before enough time had elapsed to allow them to change to the point of sexual isolation. It is unclear how much human alteration to the environment has facilitated this coming together of the races, but clearing of forest for farmland has undoubtedly benefited the species and its numbers and range have greatly expanded, especially in the east, so it seems likely to have been relevant to at least some extent.

  There is another familiar Australian species, however, where our role in interrupting evolution seems more clear cut. The bird I grew up calling a Spur-winged Plover, but now formally known as the Masked Lapwing, is a large stroppy plover with a brain-piercing war cry, which lives in open country throughout northern and eastern Australia. There are two clearly defined subspecies, which, like the magpie subspecies, used to be (and sometimes still are) regarded as full species. In the south, the formerly named Spur-winged Plover has relatively small yellow facial wattles, extensive black on its crown and conspicuous and intimidating black-tipped yellow bony spurs pointing forward from the angle of the wing. It uses these spurs without compunction while swooping and shrieking at anything that dares come within the declared no-go zone surrounding its nest on the
ground. Given that this nest can be on a school oval, playing field or grassy roadside or centre strip, this regularly creates anxious stand-offs!

  The tropical Masked Lapwing (or Plover) has enormous yellow wattles framing its face, much less black on the head and less obvious wing spurs. At the time of European settlement, it seems that the populations were separated (at least along the coast, though there is some doubt about the situation in central Australia) and heading for separate species status. However, the clearing of forests for pasture, airstrips, roadside verges and ovals created plover Nirvana and the populations spread north and south until they reunited in the vicinity of Townsville in north Queensland. Here they found that their differences were still not significant enough and they interbred, forming a broad hybrid zone, and that particular line of evolution was snipped off.

  Still in Canberra: pardalotes

  An interesting thought has really only just struck me; I’ve been fortunate enough to have enjoyed birds in quite a few, mostly Southern Hemisphere, countries, but other than chance encounters I’ve done little birding in cities other than my own. I guess I just arrive and head for the bush for the most part! Still, the birds and their stories that I’ve introduced in this chapter could as easily have been in several other Australian cities, so I hope you’ve not been too put off by my apparent partiality.

  For some weeks in spring the compost heap had to be quarantined while a pair of exquisite tiny birds took it over, burrowing deep into the soil near the bottom.

  Spotted Pardalotes are close to being Australia’s smallest birds, barely 10 cm long and weighing only 10–12 g, but their presence is powerful well beyond their physical size. The male has a black head, wings and tail generously spangled with clearest white spots, a broad white eyebrow, buff-scalloped back, red rump and bright yellow throat, breast and vent, while the female is somewhat more muted in colour. The volume of sound they produce is startling for such a scrap of bird – a clear ringingly repeated ‘dee-DEE-dee’, delivered in measured tones, which seems part of the summer air. They are common urban birds, as long as there are eucalypts to feed on: they specialise in gleaning leaves for small insects or spiders. In particular, they focus on lerps, sap-sucking bugs that use the surplus sugar they absorb, while trying to get enough nitrogen, to build little protective shelters over themselves. On a still hot day, the pattering of the lerp covers onto the dry forest floor can be surprisingly audible as pardalotes nip them off and discard them to attack the insect.