Birds in Their Habitats
Page 8
His ancestors would have once formed a single species that ranged along the warm east coast and probably far inland. Then the rains began to fail, the winds blew cold and the rainforests retreated to sheltered refuges, each separated from the rest. There were periods of amelioration when they expanded again, but never to the point when they reformed a single vast habitat. Within the isolated fragments, the inhabitants began to change, as life does, but in directions different from those their now distant relatives were travelling. Some birds, such as the hard-flying fruit-doves, could cover the distances between the far-flung forest patches, but riflebirds are not strong fliers and have no reason to venture out into the open country. As a result, where there was just one Australian species there are now three, all isolated from each other. North of my Paluma performer, way up on Cape York Peninsula, lives the Magnificent Riflebird (though what riflebird isn’t?), and far to the south, in the subtropical rainforests above and below the New South Wales–Queensland border, is the Paradise Riflebird. They all look similar but have obvious plumage differences and slightly different displays. The Magnificent Riflebird has a very different voice too: mellow rather than harsh, like a reverse wolf-whistle.
There are as many variations on this theme as there are birds in the forest, but basically this is how all species form: the essential ingredients for the recipe are time and isolation.
Cairns, north Queensland: hovering sunbird
On a rainforest edge in Cairns, north of Paluma and at sea level, a brilliant little yellow-bellied, navy blue-breasted and olive-backed bird is hovering at a red tubular flower, its long bill inserted completely in the tube to access the nectar in the gland, the ‘nectary’, at the bottom. I’ve heard it asserted that only hummingbirds can really hover but, although they are indisputably the stars, in addition to the sunbirds (many of them in Africa and Asia, in addition to the Olive-backed Sunbird hovering in Cairns) I’ve seen small honeyeaters, notably spinebills, plus weebills, gerygones, thornbills and pardalotes, among others, hovering at flowers and foliage. (At the moment I’m ignoring ‘wind hovering’, which is slightly different, but we’ll get to that at another time.) There may be a certain trans-Pacific superciliousness about this, but if I was used to seeing hummingbirds all the time I’d probably be a bit that way too.
Hovering
To see a hummer hang stationary in the air at a flower or feeder, then suddenly zip in any direction, including backwards, to rematerialise and ‘park’ in another airy place is both thrilling and counter-intuitive. In theory at least it’s relatively straightforward, involving rotating the wings in shallow figure-eights, at speeds so high that it hurts my shoulders just to think about it. Effectively they are pushing backwards at the same speed that they are pushing forwards, as well as balancing out gravity, the nett result being to hang motionless. No other bird can push forwards against the air to move backwards – they all drive only with the down/back stroke, which thrusts them forwards. For them, the forward movement of the wings (which drives a hummer backwards) is just a recovery stroke, a passive action pulled by elastic tendons. To our eyes, the hummer’s wings are just a blur – even the (relatively) lumbering Giant Hummingbird manages 10 to 15 beats a second, while small ones whirr away, very audibly, up to 80 times a second.
But – and, of course, there must always be a ‘but’ – such a lifestyle doesn’t come cheaply. The flight muscles weigh up to 30% of the bird’s entire bodyweight, at least 50% more than any other bird. This is an ugly feedback loop to be caught in – more weight in turn requires even more work to carry it. At 20% of its bodyweight, a hummingbird’s heart weighs, relatively, five times what ours does and beats up to 500 times a minute when resting. At full exertion, which seems to be most of the time, that doubles. At rest, the little bird breathes 300 times a minute (i.e. five times a second), some 20 times what we need. The huge energy required to drive the engine comes from nectar, which is the point of it all. To obtain the necessary 150% of its bodyweight in sugar solution, it must visit around 2000 flowers a day. For me, that would mean drinking 120 L a day, which in turn would put rather a strain on my kidneys. A hummer’s kidneys are very simple to cope with the volume of work, and they constantly spray out the surplus water. Although it’s almost pure water (so no need for a ‘yuk’ if you’re standing under it), they inevitably lose some electrolytes in the process, so must eat materials such as soil and ash to compensate (e.g. Ridgely 2011; Elphick 2014, pp. 95, 408; Schuchmann and Bonan 2016).
It’s a tough gig being a hummingbird, but I’m very glad that someone has to do it!
Other memories of rainforests
As unpredictable as leaves side-slipping down from the canopy, here are a few more rainforest memories:
• Through a tangle of vines and dazzle of single leaves reflecting shafts of sunlight through the canopy, an enormous Southern Cassowary stands quietly in a patch of rainforest by the carpark at Mount Hypipamee on the Atherton Tableland above Cairns. There is some menace in the air, but emanating more from my knowledge that this is a potentially dangerous animal than from any threatening behaviour from the bird. The bony-looking helmet, the bare wrinkled face and neck, red and bright blue, and the swinging red wattles below the throat, all coalesce into an oddly reptilian image.
• In the green gloom of the Amazonian rainforest in Yasuní National Park in Ecuador, a large fluffy chick sits upright in the open on the end of a broken-off vertical tree branch – and is virtually invisible. It is a Great Potoo, a member of a family of seven nocturnal species related to frogmouths and nightjars. Despite our presence, the chick is very disciplined, remaining motionless with closed eyes (or maybe there’s the narrowest slit there, watching us). Its pale grey downy plumage perfectly matches the lichened trunk alongside it, complete with vertical black wavy lines that mimic cracks in the bark. Further south in Amazonia, in southern Peru, an adult of the closely related Long-tailed Potoo repeats the trick, rigidly upright in full view on a broken branch stump. Mottled and streaked in browns and creams it takes sharper eyes than mine to distinguish it without guidance.
• Not far from the Potoo in Yasuní a Rufous-bellied Euphonia is singing almost into my face from only a couple of metres away. It’s fair to say that from my perspective it’s not an overly impressive song (despite the genus name meaning ‘euphonious’), being more reminiscent of a buzzing insect, but the bird and the situation are what grabs my riveted attention. He is shining deep blue above and orange below – and we are both 45 m above the ground (see Photo 9). However, while he is perched on a fairly flimsy branch, I am on a sturdy wooden platform attached to a magnificent old Kapok Tree. I’m not fond of heights, but the privilege of being on the same level as the canopy-dwellers is one not to be forgone.
• Thousands of kilometres to the south in Chile, in a very different Patagonian rainforest, cold and sodden, dominated by ancient Nothofagus trees – very similar to those in New Zealand and Tasmanian beech forests – a pair of huge Magellanic Woodpeckers is showering the mossy forest floor with chips of wood splintered from the trunk. With good reason, these birds are known as el carpintero: the carpenter. Beyond them, white icebergs, calved from a glacier, drift in a grey lake. The echoing of the hammering had brought us to them – magnificent black birds, the male with bright red head and wispy crest, the female with just a ring of red around the base of the bill. We watch until they fly off into the next swirl of mist and chilly rain.
References
Elphick J (2014) The World of Birds. CSIRO Publishing, Melbourne.
Fiske P, Rintamäki PT, Karvonen E (1998) Mating success in lekking males: a meta-analysis. Behavioral Ecology 9(4), 328–338. doi:10.1093/beheco/9.4.328
Hill GE (2010) Bird Coloration. National Geographic, Washington DC, USA.
Marks JS, Cannings RJ, Mikkola H (2016) Typical Owls (Strigidae). 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,
Mikkola H (2014) Owls of the World: A Photographic Guide. 2nd edn. Firefly Books, Buffalo NY, USA.
Ridgely R (2011) Hummingbirds of Ecuador Field Guide. Jocotoco Foundation, Quito, Ecuador.
Schuchmann KL, Bonan A (2016) Hummingbirds (Trochilidae). 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,
Simpson J, Roud S (2003) A Dictionary of English Folklore. Oxford University Press, Oxford, UK.
Turner DA (2016) Turacos (Musophagidae). 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,
Winkler H, Christie DA (2016) Woodpeckers (Picidae). 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,
3
Oceans and islands
The Galápagos: oceanic islands
As I waited with my friend Juan – a top-rank Peruvian nature guide, all-round fixer and excellent travel companion – we were aware of sparrows flitting through the open airport building and heading for the al fresco café. Almost simultaneously, the realisation struck us – there are no sparrows on the Galápagos, and we were seeing our first ‘Darwin’s finches’. For a moment we stared at each other, then grinned.
Flying into Baltra airport for the first time was one of the most exciting moments of my naturalist’s life. It was then an open-sided very rustic building set in a spectacularly barren black volcanic landscape by the Pacific Ocean in the centre of the fabulous Galápagos Archipelago. (Since then a flash new terminus has replaced it, very nice and admirably ecologically sound with regard to energy and water conservation, but without the same charm.) During the Second World War the US used it as a base for patrols aimed primarily at protecting the Panama Canal. When the war ended, they had no further use for it and handed it over to the Ecuadorian Government. It now doubles as a military base and civilian airport for the huge numbers of tourists who fly into this naturalists’ mecca every day (see Photo 10).
‘Darwin’s finches’
The quotes around ‘Darwin’s finches’ are there advisedly. The ‘Darwin’ appellation was not applied until well into the 20th century and, despite appearances, they are certainly not finches (or sparrows!). Charles Darwin, the unknown young naturalist who was yet to grow into the towering figure of 19th-century biology, visited the Galápagos on the Beagle in September 1835; he spent 5 weeks of his 5-year epic voyage there, visiting just four of the islands. His observations there famously sparked his understanding of the nature of evolution, as expounded in the scientifically pivotal book On the Origin of Species. Except that they did no such thing at the time! His field work on the Galápagos was, by his own later admission, not his finest hour, but being the man and scientist he was, he certainly learnt from the somewhat embarrassing experience. He did collect some finches, but he assumed that those that looked the same really were all the same – the islands from where he took them are mostly in sight of each other and he assumed the archipelago would be biologically homogenous – and he failed to keep proper notes as to the origins of the individual skins. In addition, he was more intrigued by the three subtly but clearly different mockingbird ‘forms’ he encountered, each restricted to its own island and obviously related to a South American species, and took his eyes well and truly off the finches.
When Darwin was in the Galápagos, he was still a conservative thinker by the standards of his own intellectual circle, and didn’t accept the prospect of species changing. It was at least 18 months later, back in England, that he began to realise the significance of what he had. Even then, his first thoughts in those important directions, pondering whether species might not in time come to beget other species, were prompted by fossil mammals from the South American mainland. In those days, he thought of himself as a geologist rather than a biologist (though a naturalist then had perforce to be a competent generalist). He collected across the board wherever he went in South America: fossils, rocks, plants and animals. He had sought the advice of London Zoo taxidermists before he left to ensure his collections would be properly preserved. For the most part, his servant Syms Covington did the actual bird collecting.
Back in England in October 1836 he started the massive task of finding scientists who were capable of identifying his mountain of specimens, and available to do so. The birds were well down his list of priorities, but in early 1837 Darwin handed them to the up-and-coming John Gould, ironically a staunch creationist (a year before Gould sailed for Australia, but that’s a whole other story). Within a week, Gould had come back with some startling – and, for Darwin, somewhat embarrassing – information. The apparently disparate collection of American blackbirds, finches, wrens and ‘gross-beaks’ all formed ‘an entire new group of ground finches’, with very different beaks and behaviours.
This was where Darwin was embarrassed, when it transpired that he had not seen the need to record from which particular islands each of this hotchpotch of specimens had come. Fortunately for him, he recognised the need to rectify his error, and Captain FitzRoy, FitzRoy’s steward and Covington had all kept specimens and been more assiduous with recording their origins.
Darwin was a meticulous and cautious scientist, and never a healthy one, and he dreaded public exposure and even more the obloquy that he knew would come his way. It took more than 20 years for him to learn the new skills he believed he needed and to experiment, but eventually and reluctantly – nudged by the young Alfred Russel Wallace who was coming independently to the same conclusions in the East Indies – he published On the Origin of Species in 1859 and in important ways the world changed. There was initial resistance from the scientific and church establishments to the concept that species were not immutable, but much more resistance to the proposal relating to the mechanism – that of natural selection. Among scientists in particular, and even among the wider population, the idea of evolution had been pretty fully accepted by the time of Darwin’s death in 1882; by the end of the century, it had ceased to be controversial.
The same could not be said of the natural selection concept. It left no role for a benevolently guiding deity to change species at their appointed time: everything is random, and nothing can be ordained. It took decades more for this to become a general orthodoxy.
Meantime, the finches knew nothing of this – and as far as I know, nobody has told them until this day, though they have been the subject of some of the most meticulous and exhaustive studies into the nature of evolution in a wild animal ever undertaken. Daphne Major is a volcanic crater rising from the sea within sight of Baltra – the plane you came on is likely to have flown right over it when landing. It is treeless, waterless and with no jetty or beach; researchers and all their needs must be landed from a pitching boat onto a ledge on a low cliff face. From there, all water, fuel, food, camping gear and research equipment must be carted up a steep track to the only possible camping site, which, of course, is shadeless. In 1974, the remarkable Rosemary and Peter Grant (British biologists based at Princeton), first went to Daphne Major to study the finches. For over 40 years they and their students have spent 6 months of every year on the exposed island, studying the Medium Ground Finches to the level of marking, taking detailed measurements of and DNA samples (from blood) from every single one that hatches on the island.
The environmental pressures on the birds are immense, with El Niño years of intensely cold scouring rains and La Niña times of crushing drought and food shortages. In the drought situation, birds with larger beaks do better because they can crack open bigger seeds than they usually eat, while their neighbours with the misfortune to have hatched with smaller bills simply starve. As a result, after the 1977 drought, the next generation had bills 3–4% larger than their par
ents’ generation did. However, in the El Niño part of the cycle, the advantage swings in the other direction. The plant producing the small seeds does so prolifically, and the large-billed finches have trouble managing them; now it is an advantage to have smaller bills to harvest the seeds efficiently. The Grants’ studies were among the first to follow evolution in a timeframe that even humans can comprehend. In just those 40 years, beak shape and size have changed significantly, not just in one direction, but swinging over generations on both sides of a mean. For more information in a highly digestible form, I couldn’t do better than recommend Jonathon Weiner’s Pulitzer Prize winning The Beak of the Finch (Weiner 1994).
I have circumnavigated Daphne Major – there are strong restrictions on landing there by anyone other than researchers – and wondered at many things while doing so. I have marvelled at the extraordinary dedication and resilience of the researchers and their attention to every minute detail for decade on decade in a very difficult situation; I doubt that I could even manage the landing! I’ve pondered the skill and experience that enables them to know every finch on the island by sight: the population fluctuates between 300 and a thousand individuals, and a new generation comes along every year. I have loved the symmetry of the story, from Darwin’s eventual realisation of the profound implications of all 17 of the Galápagos ‘finches’ apparently arising from a single ancestor, to the Grants’ work in the same place taking his ideas to a more complex plane than he’d imagined. (The number of species recognised has recently risen, following very comprehensive genome sequencing; Lamichhaney et al. 2015.) And I’ve shaken my head at the concept of the little birds surviving against all apparent probability on such a bleakly inhospitable site.