Thursday, 9 March 2017

Ratites; the ancients of the bird world. #1 Who are they?

Across the southern lands are (and in some cases were) scattered a series of mostly giant, flightless birds, whose significance we often overlook. We call them the ratites, from Latin for a raft, a reference to the flat breastbone - if you no longer fly, you no longer need either the great flight muscles (some 15% of your bodyweight) or the keel on your breastbone to anchor them. 
Emus Dromaius novaehollandiae near Esperance, Western Australia.
Their significance in the world of birds is their undisputed role as The Elders. The most fundamental subdivision of the world of birds is not, as one might expect, into Passerines and Non-passerines, but into the Palaeognaths (the 'ancient palates') and the Neognaths ('new palates'). The details of the palates needn't concern us here, but the elemental subdivision thus created certainly does, because the Palaeognaths comprise just the ratites and their associated 'sister group' the South American tinamous (but more on them later). It's just them versus every other living bird!

Since we've started this introduction to them in Australia, we might as well continue here. When Europeans arrived here there were probably three species of emus. The small emus on Kangaroo Island (off the coast of South Australia) and King Island (in Bass Strait between the mainland and Tasmania) are generally regarded as separate species (D. baudinianus and D. ater respectively), but the evidence is tragically limited, with only one and three skins respectively surviving. Some authorities take a more cautious approach and regard them as sub-species. There were also Tasmanian Emus which were almost certainly the same species as the mainland birds; they were gone by the 1860s, while the other two were exterminated horrifically soon after the arrival of Europeans in the early decades of the century.
Kangaroo Island Emus, by French self-taught natural history artist Charles-Alexandre Lesueur, who
sailed with the Baudin expedition of 1800-1803. While visiting Kangaroo Island they captured two
unfortunate emus and took them back to France.
On the mainland they're still doing well, though they retreat from settlement and are now very rare in the south-eastern highlands. I'll talk more about Emus than the others, both because I know them best, and because much of the information about them can be used to compare the others.

Emus on the Hay Plain, south-western New South Wales.
They are found across all of inland Australia, where they are nomadic, following the rains and feeding on seeds or fruits or caterpillars or grasshoppers as conditions dictate. This nomadism and their disdain for fences has led to many of their problems with European settlement. In Western Australia the 'Great Emu War' of 1932 was fought between migrating mobs of over 20,000 emus, and the Australian army with machine guns and grenades, called in by the WA government. Jock Marshall in his pioneering conservation work The Great Extermination (published in 1966, just before he died, far too young) reports "History does not record the name of the CO emus, but he must have been a good chap". It seems that perhaps only a dozen emus were killed, and the government had to withdraw the military to save them from further embarrassment.

Like most ratites, Emus are polyandrous, though they start off the breeding cycle as a pair in mid-summer, and dally for about five months. In late May and June she lays up to 20 large dark green eggs in a scrape on the ground, totalling up to 15kg. Not surprisingly, she reckons by now that enough is enough, and she plays no further part in the process, though if she’s still feeling frisky she can go off and do it all again with someone else! Each time she leaves the father in sole charge. He broods for eight weeks, and during the whole time he lives off his body reserves without eating, drinking or defecating, rousing only to turn the eggs several times daily. In this part of the world eggs were apparently laid in about July, which meant that the male was incubating in the snow.

Emu eggs, north-western New South Wales.
In South America rheas are even more Bohemian (from a very anthropomorphic perspective!). The texts tell us that “males are simultaneously polygynous, females are serially polyandrous”, which means that males become territorial, while females form small mobile groups which roam around seeking collective dalliance with likely-liking blokes. He mates with the group of females who all lay eggs in his nest, then go off to look for another bloke to do it all again.  

Darwin's Rhea Rhea pennata and chicks, Torres del Paine NP, Chilean Patagonia.
Kiwis on the other hand are always monogamous, while ostriches can be monogamous in harsh desert situations, though their usual approach is much more complex. A dominant male and female share brooding duties, while in the same territories subordinate females mate with multiple subordinate males and leave them to get on with, as with the emus. At the same time roaming males pass through and mate with the females, but it's not clear who ends up holding the baby in that situation.

The striped Emu chicks can walk within hours, and run and swim within a week. As they get older, they are distinguished from older birds by a dark neck and head. Dad cares for them for 18 months, so he only breeds every other year.
Emu with young chicks near Cue, inland Western Australia.

Father and older chicks, northern Flinders Ranges, South Australia.
All more modern birds have feathers which 'zip together' by tiny hooks on the barbules along the edge of each barb, hundred of which branch from the central vane, or rachis. In ratites these hooks are missing, so the plumage is much looser and more hair-like than we're accustomed to seeing in a bird. An Emu can be somewhat reminiscent of a haystack in fact.
Shaggy Emu plumage.
Something else is happening here too though. Some birds, especially more primitive ones, have an aftershaft, like a small second feather, branching from the base of their feathers; passerines mostly lack them. They tend to be woolly and it seems as though their purpose is primarily insulation. In Emus however this aftershaft is the same length as the main shaft, and in fact it is generally not clear which is which. You may get a sense of it in the photo above, but here's a single Emu feather. They share this oddity with cassowaries, which are in the same family.
Emu feather; the aftershaft is as long as the main shaft.
In kiwis and cassowaries, the plumage is much coarser and hairlike, probably for waterproofing, at least on the exterior; the underfeathers tend to be woolly.
Southern Cassowary Casuarius casuarius, Etty Bay, north Queensland.
One more thing on Emu plumage; they have a somewhat curious 'part' down the back, with the feathers falling away on either side of it.
Emu drinking near Esperance, Western Australia; note the conspicuous part along the spine.
All ratites have three toes, except for ostriches, which have reduced that to two. All except the forest-dwelling kiwis and cassowaries are birds of the open plains, and all except kiwis are runners. All of these can easily maintain speeds of 50kph, and the smaller rheas up to 60kph; an ostrich when pressed however can reach 70kph. 

Emus and cassowaries are in the same family, but the other groups each form their own family. There are three species of cassowary, all found in New Guinea, while the Southern Cassowary is also found in the rainforests of north Queensland, to where it doubtless walked during a glacial period when Torres Strait was dry - this last happened only 10,000 years ago. Their most obvious characteristic is the tough flexible casque on their head, whose purpose is still debated. It was supposed that it helped in running through dense vegetation, but there is no evidence for that. Captive birds have been observed using it to shovel litter aside, and it probably also has a display purpose, along with the colourful neck wattles.
Southern Cassowary, Mount Hypipamee NP, north Queensland.
Cassowaries are primarily fruit-eaters and are important vectors of rainforest fruit seeds. It has very recently been shown that the seeds of the Javan Ash Ryparosa javanica, a rainforest tree from north Queensland, germinate far better if fed first to a cassowary. In fact, over 90% of seeds taken from cassowary droppings germinated, compared with only 4% of uneaten seeds. Javan Ash seeds incidentally have one of the highest levels of cyanogens ever recorded in a plant, but presumably the birds pass them through quickly enough and without breaking the surface of the seed, so that they are unaffected.

In Africa there are two ostrich species, as the result of a recent recognition that the Somali Ostrich of far north-east Africa is a separate species, Struthio molybdophanes, from the much more widespread Common Ostrich S. camelus.  They are the world's largest birds, males standing up to 2.75 metres tall and weighing close to 150kg. Unlike other ratites males and females are very different; males are far larger, but are also black and white, compared with the females' duller grey-brown tones. 
Male Common Ostrich, West Cape NP, South Africa.
There are five species of New Zealand kiwis, relatively small forest-dwellers with characteristic long down-curved bills and highly developed senses of smell for finding worms and arthropods in soil. They are primarily nocturnal, though this may be only since the advent of humans and associated predators. They form a life-long pair bond; a kiwi's egg may be 25% of its body weight, making it the largest of any bird.

North Island Brown Kiwi Apteryx mantelli;
photo courtesy Wikipedia.
In South America there are three species of rheas, though until recently only two were recognised. Rhea was the mother of the classical Greek gods and goddesses, but we have no idea why Paul Mohring, the German biologist, applied the name as a genus in about 1750. While brooding, the male is very aggressive, to the point that once he’s started brooding further females laying eggs must leave them outside the nest, and leave him to pull them in. Their food focus is on broad-leafed plants, but they also eat seeds, roots, fruit, insects, and small vertebrates. As ratites go they are relatively small, only a metre tall and with relatively long wings; this enables their very impressive turn of speed.
Darwin's Rhea Rhea pennata and chick with Guanaco (which gives an idea of how relatively small the bird is)
Torres del Paine NP, southern Chile.

Darwin's Rheas near Punta Arenas, on the Strait of Magellan, above and below.

There were apparently seven or eight of the mighty elephant birds of Madagascar, in two genera; the largest of them stood three metres tall and weighed up to half a tonne. They survived until recent times, until the arrival of humans, who presumably hunted them and their eggs to extinction. They were certainly present within the last 1000 years, and there are accounts attributable to them much more recently than that. 

The same sad tale could be told of the nine New Zealand moa species, the largest of them standing a colossal 3.6 metres high and weighing close to 250kg. Unlike all other ratites they had lost even their vestigial wings; presumably as forest-dwellers they were not runners and had no need of them for balance. They disappeared only some 600 years, overhunted by the newly arrived humans.

The conventional story of ratites is that they are a classic example of old Gondwanans, scattered across the southern lands as the continents took them on their journeys. That is the story I want to examine next week - be prepared for surprises if you've not hitherto heard this one!

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