Birds in Their Habitats

by Ian Fraser

  This is by no means the only water-based display, however, and why would a waterbird not choose its major habitat as its stage?

  Cocha Salvador, Peruvian Amazonia

  Cocha Salvador at dawn is a special place to be. The mist rises from the surface of the big deep lagoon and primary rainforest crowds down to the shores. Across the water rolls the essential sound track of Amazonia: the pulsing wind-like roar of the howler monkeys.

  It’s not an easy place to get to. We had travelled for 2 days in a motorised narrow river boat from the frontier river port of Atalaya down the Alto Madre de Dios River, then up the Manu River to the basic lodge run by the Machiguenga people. This morning, in the dark, we got back into the boat to travel downstream again, then walked through the gradually lightening forest to a little jetty, where we clambered onto a heavy rough-hewn raft that our indomitable bird guide Ribelino poled slowly across the water.

  Other waterbird dancers

  In the Sacred Valley of the Incas in the Andes near Cusco in southern Peru, the Urubamba River rushes cold and ice-green beneath mountains scored by ancient agricultural terraces, built and worked before the Incas imposed their rule on the valley. The water foams and crashes furiously onto the huge boulders in the stream, hurling itself in boiling torrents through channels between the rocks. Clearly nothing of any size could survive in such a maelstrom. And yet …

  One morning I walked from our riverside hotel to the edge of the little gorge through which the Urubamba cascades – and saw something remarkable. Three slender long-tailed ducks were standing on the rocks, water racing over their feet. Two were dark-bodied with white heads slashed with a black line from the red bill through the eye to the base of neck; the third was dark above and brick red below. The white-heads were whistling loudly, beaks held high, the shrill calls cutting through the river’s roar. I knew they were Torrent Ducks: specialists in the wild Andean streams along the full length of South America, from close to the Caribbean down to Tierra del Fuego. I was surprised though: Torrent Ducks are noted as faithful partners for as long as they both live and real home-bodies, fiercely defending a territory which stretches for a kilometre or so along the river. Nonetheless, here were two males (the white-heads) clearly competing for the female’s favours. She was watching the whistling duel with some interest, but was in no hurry to make a decision.

  Then, startlingly, they were all in the maelstrom, swimming strongly upstream! And from I knew not where, a third male suddenly appeared and joined the competition. The three males led the way, whistling constantly and showing off their power and skill in the horrific conditions, while she followed them, still presumably taking notes. This enthralling performance continued, on rocks and in the water, for some time until we finally had to leave. I can only assume that she had recently lost her mate and that the others were singles cruising and looking for such an opportunity; it is reported that males at least usually find a new mate within a week of losing one (Cadona and Kattan 2010).

  Perhaps the most famous of the water dancers, however, are the grebes: a truly venerable and worldwide Family of divers with apparently no close relatives. An important difference between their displays and those of the ducks I’ve described is that only the male ducks perform while the females watch and judge. But in grebes both members of an already mated pair participate equally, often swapping roles. Many years ago I was working at the Coorong, a hugely atmospheric long narrow lagoon stretching south from the mouth of the Murray River in South Australia for 150 km and separated from the wild Southern Ocean only by a strip of sand dunes. I found a gap in the reed beds and crouched and peered through, just in case … Good move!

  I was mesmerised by what I saw. A pair of magnificent Great Crested Grebes was only 30 or so metres away on the water, entirely engrossed with each other. These are big birds: up to 60 cm long and weighing up to 1.5 kg, with a long neck and straight sharp fish-snatching bill. The body, generally low in the water, is dark and unremarkable – but the head! The black forehead rises to a spiky black erectile crest, while below that a white face surrounds a red eye. The rich rufous sides of the head sweep back to a glorious mane of black-tipped chestnut feathers. In the Northern Hemisphere they lose these adornments in winter, but in Australia and Africa (this is a very widespread species – or perhaps a species group – absent only from the Americas) they remain magnificent all year round.

  The two Coorong birds were sitting in the water facing each other, in silence, turning their heads from side to side with raised crests, sometimes bending their necks backwards so that their heads touched their backs to rearrange some feathers, from time to time quickly shaking their heads or nodding them to fan their manes out to show their full glory. After a few minutes it seemed as though it was all over as they turned and swam away from each other, then slowly sank beneath the choppy surface. Suddenly one, then the other, resurfaced with a beakful of water weed. They swam right up to each other, then rose in the water breast-to-breast, rocking their heads from side to side in unison, paddling furiously to stay erect. I was breathless, so I can’t imagine how they were feeling! I’ve since learnt that this is called the ‘weed ceremony’ and is practised by Great Cresteds all over the world, but it was a revelation to me at the time (and I’ve never seen it since).

  The closely related Western and Clark’s Grebes from North America have an element to their display which is, if anything, even more dramatic. After some head-shaking foreplay, a message is exchanged by a quick look between them, then they rise completely out of the water so that body and neck are vertical, with head held stiffly forward and wings held stiffly out behind. Astonishingly, they rush across the water in a way that seems to suspend normal laws of physics – they run on the surface. They do it via the expenditure of huge amounts of energy, pattering their splayed webbed feet at something like 20 little steps a second on the surface, keeping perfect pace side by side with each other. After a few seconds, and some 20 m, they perform a synchronised dive and disappear.

  But why? In the case of the ducks, it’s relatively obvious. The male is showing off his fitness and, I suspect, his capacity as a survivor – it must take years to perfect the Musk Duck’s complex rituals and, as well as demonstrating his strength and resilience, he is declaring that he has genes that have enabled him to live a long life, no small advantage. Those are the genetic edges that any discerning female Musk or Torrent Duck wants for her offspring.

  But what about the grebes’ elaborate dance, which is apparently mostly performed by already established couples? Here, it seems to me, we don’t really have firm answers, though there are some assertions regularly repeated. I am bearing in mind that displays such as those of the grebe pairs are immensely expensive in energy, in time (which could be perhaps better spent in feeding or nest-building, for instance), in production of otherwise unnecessary display plumage and in the risk of attracting predators. It is often suggested that such behaviour enables birds of similar species to ensure they’re not making a very embarrassing mistake in their choice of mate. There are such similar species pairs, including Clark’s and Western Grebes, but surely any confusion can be only in our eyes? I would be very surprised (though in fact I often am!) if Clark’s and Western Grebes really needed to undertake complex recognition tests to know if a bird was of their own species or not. And wouldn’t a simple vocalisation be a lot more efficient if such a test was required? In any case, that is certainly irrelevant to the Great Cresteds, which resemble nothing else.

  Moreover, it’s a red herring if the pair has already mated. It is said that displays in monogamous species (which may mean a lifetime pairing, or just for one season) are to re-establish links, though it’s not clear why that is necessary if breeding has already commenced. Is it necessary to periodically check on your mate’s continued commitment? Or their continued fitness? Well, perhaps. Life-bonded birds such as albatrosses undertake elaborate displays, especially at the nest, with song and bill-clattering dance (see Photo 20).
In their case, they are taking it in turn to forage at sea for extended periods while the other broods the egg. Could it be that the display assists in assessing the fitness of the stay-at-home partner to stay on the nest without feeding, so that the forager can judge how long it’s safe to be away? That sounds a bit far-fetched, but I think it’s plausible.

  That can’t explain the grebes’ dances though. Moreover, it seems that most grebes form a pair bond only for one season. Is it possible that in their case at least we have consistently misunderstood and that the dances are mutual tests of suitability to share this season’s reproductive adventure, rather than reaffirmations? Probably not, but it would at least be easier to understand if that were the case. Perhaps it is a process – an extended courtship during which bonds are gradually formed – which only ends when eggs are laid. If so, that might explain why it is unclear from the written accounts if the dancing pair are ‘an established item’, or only just becoming one, but that really only begs the bigger question. Why would such an expensive and exhausting process be necessary, or even advantageous?

  In all the accounts I’ve been able to find, these questions seem to be skipped over – though of course it could just be that I’m missing something obvious; it would hardly be the first time! However, far from being depressed by my ignorance, I revel in all the things that I don’t know and, as in this case, even those that we collectively don’t seem to know. That is not to say that I think that ignorance is bliss – I will lie awake gnawing at a question that I can’t think of a plausible answer to – but I do love being reminded of how much we in general (and me in particular) have to learn. It would be a grim day indeed, for a couple of reasons, if I were to awake one morning and decide there was nothing left for me to discover! Inter alia, my ignorance helps me remember just how trivial I am in the overall scheme of things, and that’s a most important reminder.

  Cocha Salvador is a very large oxbow lake (a billabong in Australia): a former great bend of the Manu River cut off by floods and now forming a deep still backwater draped with rainforest (see Photo 21). It is in the Manu Reserved Zone: a vast lowland rainforest wilderness within the Manu Biosphere Reserve, inhabited by indigenous people and only otherwise accessible to researchers and visitors accompanied by authorised and environmentally trained guides. Cocha Salvador is in this reserve, not in Manu National Park as often claimed in websites of companies who go there – the park itself is even further upstream, and is closed to all visitors except authorised researchers. We had the lake to ourselves; only one group is allowed on it at a time, and Ribelino had ensured that we got the prized first turn on the water.

  One of our main ‘targets’ for the morning was one of the most impressive, and rarest, big mammals in South America. The big oxbow lakes – and they are few – are key habitats for Giant Otters, an endangered species across their northern Amazon Basin range. Heavy hunting for skins has reduced their numbers to no more than 5000; the species is listed as Endangered by the International Union for Conservation of Nature. Even in remote Manu, it is estimated that only a dozen families survive, and one of these is in Cocha Salvador. We were enthralled by our encounters with the family of huge otters – up to 1.8 m long and weighing up to 30 kg (though much larger animals were reported before the days of intense hunting). They share the cocha (from a Quechua word, the language of the Inca empire) with their mortal enemies, the Black Caiman, largest of the alligators, which can grow to 5 m long. Both otters and caiman prey on each other’s youngsters; the otters will also team up to attack larger caiman. We watched the otters bring big fish ashore to share, albeit tetchily, all the while squealing and whistling and whining.

  It was thrilling and engrossing, but this is a book about birds and something else remarkable was happening at the cocha; no fewer than four single-species bird Families were present!

  Single-species Families

  Any birder is interested in a bird species which is the only member of an entire Family (birds with no close relatives, and for which it is often unclear just what even their more distant relationships are). They don’t come along every day; there are something like 10 500 living species of birds, and only 30–35 (depending on which taxonomy you use) of them are alone in their Family. Tools, especially biochemical ones, are improving all the time and new ones are being developed, but ultimately it still requires the experience of a scientist (or more usually a team) to make a judgement as to whether the differences revealed in the chromosomes or the proteins of two birds represent evidence of one or two species, or even Families.

  New tests can reveal unsuspected differences. Until very recently, the apparently unremarkable little Spotted Wren-babbler of the dense mountain thickets of eastern India, China and South-East Asia wasn’t even regarded as in its own genus, but was included with eight other species of Asian wren-babblers in the large Old World babbler Family. Then a major in-depth study of a very large number of mostly Old World passerines, published in 2014, threw up the totally unexpected result that the unassuming Spotted Wren-babbler was royalty, having its origins way back in the early days of passerine evolution and losing any relatives long ago; it has an entire Family all to itself (Alström et al. 2014). To reflect this, it is now known as the Spotted Elachura, which is also its new genus name.

  The reverse can also happen, for a couple of different reasons. First, in a mirror image situation of the Elachura’s, a bird previously thought to be unique can be reinterpreted as more closely related to another bird group than was believed. In the case of the Sapayoa of Panama and northern South America, many eminent people now think it to be more closely related to another bird group than was believed even possible (e.g. Moyle et al. 2006)! The highly influential International Ornithological Congress (IOC) believes that the Sapayoa belongs with the Old World broadbills: a Family of primitive suboscine passerines (see page 46). This would make it the only American member of the Old World suboscine grouping, which includes broadbills, pittas and the Madagascan asities. (Not for nothing is its species name aenigma!) Not everyone is convinced by this, and some would retain its single-species Family status, but it illustrates the point.

  The other way in which a single-species Family bird can lose its coveted status (coveted by birders, if not actually the bird) is if it is revealed that two species have actually been masquerading as one. This is the case with the Ostrich, for instance: most ornithologists now think that the Somali Ostrich of the Horn of Africa is a separate species from the more widespread Common Ostrich. Likewise, the IOC would split the Osprey, raising the Eastern Osprey of Indonesia and Australia to full species status, thus robbing its Western relatives of their special standing.

  However, the four Robinson Crusoe species (i.e. all on their own) that we saw that morning at Cocha Salvador seem to be in no danger of losing their status, though some would include the Donacobius with the wrens. Even in this case, though, the main proponent of the stance among the major world taxonomy players, the highly respected Handbook of Birds of the World, acknowledges that the evidence is shifting away from it. Let’s start there.

  The Donacobius (or Black-capped Donacobius, though there are no others from which it needs to be distinguished) is a medium-sized passerine with a long tail, not unlike a mockingbird (with which it has also been included). Dark above and rusty below, they sit in pairs or small groups high in fringing rushes and reeds and whistle at passers-by on the water. They are found around waterways throughout much of lowland northern South America.

  The other three were all non-passerines. Of these, the Limpkin looks perhaps the most ‘normal’: a bit like a brown ibis with a black and white speckled neck and a slightly curved bill. Its nearest relationship seems to be with the cranes. It prowls the water’s edge with a distinctive high-stepping gait (which allegedly gives rise to the name, though it doesn’t really resemble limping), searching for the big snails that are the mainstay of its diet. It deals with them in a very similar way to that of the openbill storks (see p
age 98): an excellent example of parallel evolution. Its wonderful wild harsh squealing calls appeared in many Tarzan movies (set, of course, in Africa), and most recently they gave their voice to the mighty and chimeric Hippogriff in the Harry Potter movies (see Photo 22).

  By comparison, the elegant Sunbittern looks like nothing else: a large bird, half a metre long, with a long body compared with its height. The plumage is grey and rufous with attractive camouflage bars. The legs, slender neck and bill are of moderate length; the head is black with two white stripes from the bill to the back of the head. Unfortunately for us, the bird we admired simply stalked along a log and disappeared into the foliage, but had it felt threatened we may have been treated to a wonderful display, the wings opening out to appear huge, featuring big semi-circular chestnut patches edged with black on a mustard background, like scary eyes. The tail fans out to close the gap between the spread wings, so it resembles a huge fan or butterfly. It is close to being an even greater rarity – a species all on its own in a complete Order – but it is now generally agreed that the equally enigmatic Kagu of New Caledonia, which also forms its own complete Family, joins it as the only other member of the Order.

  All this was pretty breath-taking, but then there were the Hoatzins! I regret to have to say that these splendid birds are, by any standards relating to most birds we know, seriously weird. You can’t say ‘it’s a bit like a …’, because whatever bird you were thinking of inserting for comparison, it isn’t! It should be no surprise at all that their singularity doesn’t end even at the Family level: they are unequivocally unique at the Order level. Only one other bird in the world (the Cuckoo-roller of Madagascar and the Comoros) can make that claim, though the ostriches, Kagu and Sunbittern come close for the different reasons discussed above. Hoatzins are always a highlight for me of any visit to the Amazon. I can’t wait to see them, and I can’t wait to show them to others. A Hoatzin is a substantial lump of a bird, 65 cm long and chook-like in general proportions, though in nothing else. It’s not surprising that they look like nothing on Earth: astonishingly, their ancestors separated off from the rest of the land bird line 64 million years ago (i.e. around the time a mighty meteor took out all the dinosaurs except for the birds), and they have been flying solo ever since! (Prum et al. 2015) (see Photo 23).