by Ian Fraser
Birds with a sense of smell
We now know that many birds really do have a good sense of smell, and some of them a very acute sense indeed (e.g. Balthazart and Taziaut 2009; Rajchard 2008; Averett 2014; Corfield et al. 2015). Kiwis have exceptional abilities to sniff out food, especially earthworms, in night-time forest soils: a kiwi’s olfactory lobe accounts for a full third of its brain according to some accounts. The Turkey Vulture and its relatives can detect ethyl mercaptan, which is released by decaying flesh. (This skill has been used by pipeline engineers: ethyl mercaptan is added to natural gas to enable humans to identify a gas leak, so vultures are experts at finding a leak in a natural gas pipeline!)
Another group of birds with a remarkable sense of smell is the petrels, which we now know can find dimethyl sulphide (or DMS, a chemical released by crushed krill, as happens when birds or other animals are already feeding on them) at sea from tens of kilometres away. They follow the scent, zig-zagging upwind, to the source. Moreover, we also know that the DMS is released by krill not just randomly across the open ocean, but especially where underwater features such as mountain ranges are close to the surface, which is where plankton tends to accumulate. With this information, the petrels not only can follow their beaks to find food, but develop a map of the oceans (e.g. Nevitt and Bonadonna 2005; Nevitt 2008). A downside of this skill is that various plastics, which are dumped at seas in vast quantities, react with algae to release DMS, which encourages seabirds to eat them and starve to death (Savoca et al. 2016).
Various members of this Family, which nest in burrows and return to them in the dark, recognise their own home by its distinctive aroma. And a final twist to this story: in 2012, it was shown that European Storm-Petrels can reliably distinguish relatives from unrelated birds by scent, and consistently preferred the unrelated ones when it came to choosing a mate. This was the first time this had been demonstrated, but given the importance of avoiding inbreeding as far as is possible, it probably won’t be the last (Bonadonna and Sanz-Aguilar 2012).
It is ironic that it is the Turkey Vultures, along with the closely related two yellow-headed vultures, which have the power of smell, because it was the experimental observations of them by US bird artist and would-be ornithologist John Audubon in the 1820s that virtually closed the door on any further consideration of the concept of bird olfaction for a century and a half. Having observed the vultures attack a meat-less sewn-up deer carcase, then circle above but reject a hidden rotten pig body, he deduced that they couldn’t smell anything. What he could – and indeed should – have otherwise deduced was that the vultures did indeed find the deer by sight, but also found the covered pig by scent, whereupon they decided it was just too ripe for them! It turns out that they prefer their carrion to be no more than 4 days old. The opinion among some of the modern olfactory biologists, whose quest to have their field taken seriously was long in vain, is that Audubon should have stuck to his day job. In the forests the three scent-detecting vultures come into their own. They can find a corpse on the ground beneath the canopy as easily as they can in the open; the big King Vulture and abundant Black Vultures must keep an eye on them and follow them down to the prize.
The rear-guard action fought, even if only in a passive way, by people who think that Audubon was basically right, but have been forced to concede that kiwis, vultures and petrels are exceptions, has been surprising. These bird groups are not exceptions to a general lack of sense of smell among birds, though they are especially good at sniffing out the world. One of the problems is that it has proven more difficult in birds than in mammals to predict their olfactory expertise from the shape of their brain, and it’s taken a while to realise that, for a bird, this is quite normal. Back in 1993, a paper was published showing that, despite a lack of evidence in the shape of their olfactory lobe, a randomly selected (by mist netting) group of five small passerines had a capacity to recognise and respond to scents, which was as acute as that of rats and rabbits (acknowledged experts in the game) (Clark et al. 1993).
Birds may not have cute whiffly noses, but don’t ever let anyone tell you that they can’t smell…
K-selected breeders: ‘have one kid, make sure it survives’
Andean Condors nest high in their rocky fastnesses, of necessity. Getting off the ground is a huge effort for a bird that is at the 15 kg limit, beyond which flying becomes very challenging (and after they’ve gorged more kilograms at a carcase they may be flightless until it digests). Accordingly, they roost and nest on cliff ledges, which are abundant in the peaks and outcrops of Torres del Paine, and along the vast spine of the Andes. In ecological terms, they are K-selected breeders, which means that they rely on the world being a fairly stable place in which life is long and death rates are low (see page 124 for more on the history of the term). In this ideal world, they can afford to have very few young and put a lot of effort into ensuring that they survive. In a human-free world, condors may live for up to 50 years, not breeding until they are 5 years old, and produce just one egg every 2 years. It is laid on an exposed rock ledge between 3000 and 5000 m above sea level; it takes 8 weeks to hatch, then the chick needs another 6 months to fledge, after which it remains dependent for another 2 years.
There’s not much room for change or error in such a plan (with only one egg every 2 years), but sadly the condor’s world has changed, and much for the worse. Torres del Paine is one of their strongholds, and they’re doing fine in the southern Chilean Andes and north to northern Argentina, but beyond that the story becomes grim. Populations have fallen badly in Bolivia, Peru and Ecuador, and to critical levels in Colombia and Venezuela. The problem comes when farmers see condors on a dead cow and assume they killed it – a story that played out for decades of tragic and pointless slaughter of Wedge-tailed Eagles in Australia. Ironically, condors are still honoured on the national coats of arms of Chile, Bolivia, Ecuador and Colombia.
Such breeding systems evolve over millions of years: it is not possible for such a long-lived, slow-breeding species to adapt to a different strategy in human timescales. All the big K-breeders, among which the plight of albatrosses is especially well known, are potentially at risk; the condors are just one glaring example among the many.
Colca Canyon: high-altitude birding
As I said earlier, condors can provide the entry to so many stories, and the condors of Colca Canyon are no exception.
Colca is an extraordinary place, some 3700 km north of the snowy peaks of Torres del Paine, well into the tropics in the arid highlands of the eastern slopes of the southern Peruvian Andes. Coming from the desert coast, the road climbs to the daunting Abra (meaning a pass) Patapampa, 4900 m above sea level. To those of us unused to such altitudes, the few steps up to the lookout present a challenge to already shocked lungs looking for enough oxygen (needless to say, the local women selling crafts by the roadside don’t seem to notice it!). The landscape is shockingly stark to our eyes – devoid of green, spurs of jagged volcanic rock protruding from the sand and stretching away to the snowy volcanoes emitting drifts of smoke on the horizon and towering 6000 and more metres into the sky. Not many birds are evident here, though I didn’t have much spare energy to go looking either! From here the road descends to the east, but not to altitudes that our lungs immediately recognise as ‘normal’.
It passes above the ancient village of Chivay through a landscape that has been subject to intensive agriculture for over 1000 years, well before the ascendancy of the Incas (though they tend to get credit for all Andean culture and technology). Terracing and irrigation supported the growing of corn, potatoes, quinoa and beans, as well as grazing flocks of Llamas and Alpacas. The pre-Incan terraces are still prominent, and are still cultivated. At these lower altitudes (though still 4000 m above sea level), vegetation is dominated by a diversity of cacti and bromeliads, including lichen-like air plants and aloe-resembling puyas with big flower spikes. Andean Flickers (big handsome tawny ground-dwelling woodpeckers with brown and white
barred back and wings, black moustache and bright red nape) hop across the ground and mount old stone walls. Dull-coloured ovenbirds such as Slender-billed Miners (which gain their name from nesting in burrows) search the track-sides for insect snacks. Bare-faced and Black-winged Ground Doves rest in cactuses among spines long enough to completely transfix them.
Then, the canyon. It is famed for being among the world’s deepest, at its maximum 3300 m straight down from the lip to the Colca River, twice the depth of the Grand Canyon, as the Peruvian publicity material is understandably fond of telling us. At the lookout where we and many others pull up early in the morning at Cruz del Condor (Condor’s Cross) Lookout, the drop to the river is a mere 1.2 sheer kilometres, but it’s impressive enough. Around the extended lookout grow the bushes bearing the long bright red tubes of Peru’s national flower, Qantuta (Cantua buxifolia), regularly visited by the plain-coloured but imposing Giant Hummingbird, which is positively lumbering when compared with its petite relatives.
Soaring: ultimate flight
However, the cars and coaches that constantly pull into the car park are not here for any of these delights, because at Colca Canyon roosts one of the last major concentrations of Andean Condors in Peru. They spend the night on rock ledges far down the precipitous walls and, as the air begins to warm in the morning, condors and air currents wake up and both begin to climb up from the depths to the sunshine. It’s never certain that the condors will rise in front of the viewing platform – there is after all a lot of canyon on both sides of here – but that morning we were in luck. It started with the hint of movement in the shadows far below, which resolved into the unmistakable bulky shape of a condor circling in the faintly stirring air, searching for the energy in the breeze to carry it up towards us. Over the next half hour or so, we were treated to the thrilling experience of 17 condors at close range, up to half a dozen at a time spiralling up to the day, soaring in big circles to gain height, and finally dispersing along the canyon and across the drab brown countryside (see Photo 16).
The silhouette of a soaring condor cannot be mistaken for anything else: massive, with a short wide tail and very broad wings tipped with seven immensely long separate ‘fingers’ comprised of the elongate primary feathers. Condors are consummate soarers, as this column of rising birds attests, not deigning to flex their wings into anything resembling flapping. Indeed, while most of these birds are youngsters and adult females, an adult male at close to 15 kg couldn’t survive by self-powered flying alone, as we have observed previously. But when we first looked at soaring, in albatrosses and petrels soaring over the oceans using the updrafts from waves and layers of moving air getting faster with height, we admired the very different shape of their wings. Those very long slender wings with low wing loading (weight borne per square centimetre of wing) are the most aerodynamically perfect shape for soaring, a realisation used by designers of gliding aircraft. So why do the condors not have such wings?
The answer is in the length of the ‘perfect’ soaring wing. We saw how the Waved Albatrosses at the Española breeding colony could only take to the air by running to the cliff top and launching into the prevailing wind. If they tried to launch into the air by flapping, their very long wings would bash against the ground and it simply couldn’t work. Most land birds can’t rely on a handy cliff to jump off, so a compromise is necessary – and that compromise is the accurately, if inelegantly, named ‘soaring wings with slots’ as demonstrated by the soaring condors. They are not the perfect soaring wing, though they can have lower wing loading than the albatross wing model, but they still endow the bird with good soaring skills while also enabling take-off from the ground or from freshwater surfaces. A condor, especially gorged on dead chulengo or cow, will probably need to run downhill while flapping to get airborne, but it can be done. A pelican will need to run across the water surface to build up momentum, but its wingtips won’t be dragging in the water.
Back at Colca Canyon, the last condors finally dispersed to do a day’s scavenging work and we left to do a walk along the canyon rim. Meantime, tour buses were still disgorging clients. I wonder if their guides hadn’t mentioned condors to them, or if they were going to attribute the lack of condors to just bad luck as opposed to their own tardiness.
‘Soaring wings with slots’
The condor’s basic wing shape (long and broad with those long ‘fingers’) is repeated in a range of quite unrelated large soaring birds. Pelicans, storks, ibis, cranes, eagles and Old World vultures have all quite independently evolved this ‘next best’ compromise wing shape for soaring. The broad wings and tail ‘sit’ on the air, absorbing its rising energy, while the slotted tips break up the turbulence around the ends of the wing, keeping the air smooth in much the way that the alula does. (For a detailed discussion of just how they do it, taking account of changing air turbulence, see Reddy et al. 2016.)
In central Queensland I have watched a dozen big Australian Pelicans and a huge lanky Black-necked Stork rising in a wide spiral above the Thomson River at the delightfully named small town of Muttaburra. All had essentially white wings – except for the tips of the feathers, both secondaries and primaries. Blacks, greys and browns are provided by a group of pigments called melanins, and it so happens that melanins also confer a significant resistance to wear, meaning that black wing tips are a very useful soaring accoutrement indeed.
The Drakensbergs, Lesotho: snow in Africa
I hadn’t really associated Africa with snow but, of course, that was just my ignorance. I’ve since seen it from Cape Town airport in the jagged ranges to the east, and in the wonderful Drakensberg Mountains in south-eastern South Africa. Here they also include the high-elevation little nation of Lesotho (formerly Basutoland), entirely enclosed by South Africa. The Drakensbergs differ from the Andes in a couple of significant ways, including being much less extensive and, at a maximum 3500 m above sea level, not as high. (Still, compared with Australia …) The Andes are still growing, forced ever upwards as the Nazca Plate pushes under the South American Plate along the Pacific coast of the continent. Earthquakes, landslides and volcanic eruptions represent Andean growing pains. The Drakensbergs (‘Dragon Mountains’ in Afrikaans, though no-one seems quite sure why) finished their growing long ago, and are slowly eroding away. The genesis of their final stage came when Gondwana began to fracture some 140 million years ago and molten rock squeezed up through the resulting cracks. This volcanic material cooled to form the hard cap to the older sedimentary rocks, leaving the Drakensbergs rearing above the surrounding lowlands to the east.
The road from Kwa-Zulu Natal to Lesotho follows the infamous Sani Pass: 9 km of gravel road (though I gather that sealing is planned for the future) climbing 1000 m up a long series of hairpin bends with precipitous drops below and black and white parapets, rock and snow, looming from the clouds above. There can be ice, snow and mud on the road at any time of year, and towards the top some pinches are at close to a one in three gradient. It is said that if you look down you can see in the gorges below the remains of vehicles that didn’t meet the criteria for success: I tried to look up at all times! This road is for 4WD vehicles only, though the Lesotho border authorities at the top are pretty relaxed about who they allow to descend. Given that the pass is in South Africa, I guess they reckon that it’s not really their problem. At one point on the road we came across an old truck broken down on a nasty switchback corner – apparently it had been there for 5 days – and we had to get out to walk cautiously past it, while vehicles ground around it in lowest gear, perilously close to oblivion.
Tolkien and the Drakensbergs
It is widely known and reported that J.R.R. Tolkien, whose father worked in a bank in nearby Bloemfontein, found his inspiration for the grim mountains of Mordor in the Drakensbergs. Isn’t it sad though when facts leap out of the shrubbery to scare a perfectly good story to death? (I guess that’s why there is a strong tendency in some places these days to eschew facts in favour of an interest
ing yarn, no matter how improbable and even disprovable it might be.) In this case, the tedious fact is that young Tolkien left South Africa at age 3 and never returned. He much later apparently reported that his only memory of the country was of a huge spider: perhaps Shelob, rather than Mordor, was South Africa’s contribution to the Rings trilogy (SouthAfrica.net 2016).
At the top of the pass in Lesotho, Africa’s highest hotel stands at 2860 m above sea level on the snowy plateau, snow piled on the roof and icicles hanging low from the eaves. Sloggett’s Ice Rats (a hamsterlike delight), Cape Sparrows, Speckled Pigeons and Drakensberg Siskins forage in snow outside. Just before that huddles the Lesotho border post: a small grim square stone building in a bleak white landscape. But what flew over was special indeed.
Bearded Vulture: digesting bones
The Lammergeier, or Bearded Vulture, is huge, with a wingspan of nearly 3 m and white-speckled black wings, tail and back, lovely orange neck and feathery trousers and a distinctive black face and beard below the bill. Despite the name, it is not especially closely related to the true Old World vultures. It has a huge, but sparse, distribution in the mountains of Europe, the Middle East and central Asia, and north-west and eastern Africa. I had never seen one, and would have felt I’d lived a very slightly poorer life had I never done so.
But what is really remarkable about the Lammergeier is its diet, up to 90% of which comprises bones! Both ‘how?’ and ‘why?’ jostle for attention but I’ll start with the how before the why leads us onto distant paths far from Lesotho’s chilly plateau. Perhaps we think of bone as being something akin to rock when we’re considering food items but, even apart from the nutritious marrow, it does have food value – if you can extract it. In fact, a study on captive Lammergeiers at Tel Aviv University (part of a breeding program for reintroduction to the wild) showed that those birds preferred bones to meat when offered the choice (Houston and Copsey 1994)! Moreover, they liked old bones more than fresh ones, presumably because they are easier to break up, and because they become lighter as they dry out, so are easier to carry away. We also know they prefer larger ones to small ones (Margalida 2008). The birds were extremely effective at accessing the organic component of the bones (sheep ribs, by the way, if you’d like to contemplate that as a diet, without the meat attached!). The Lammergeier’s task is to extract the organic component, which comprises mostly short collagen fibres (the protein that forms connective tissue), from the matrix of calcium phosphate apatite, which is of limited use to the bird, and it does so with near total efficiency. Remember, too, that there is the bonus of the fatty marrow at the end of this, but the bone itself supplies most of the bird’s nutrition.
