In October 2000, the last wild Spix’s macaw, a solitary male, disappeared from its patch of forest in Brazil. The species is not, technically, extinct: a few dozen individual birds survive in zoos and in the aviaries of private collectors, but it is now in the realm of the undead, where it will remain until either the last individual dies or – less likely – the species is resurrected in a successful reintroduction to the wild. In a hundred years’ time, it will almost certainly join the entries in a much larger edition of Extinct Birds. Errol Fuller’s book recounts the story of the eighty or so bird species known to have been extinguished during recorded history, in every case by human beings or their proxies – rats, cats, dogs, pigs and other introduced animals, plants and microbes. At current rates, the 2101 edition will run to 15 volumes – and what has happened to birds provides a good yardstick for estimating the chances of other organisms. Because they are conspicuous, their extinction is better documented than that of most other creatures. We can be reasonably confident that nearly all the bird species that have survived until the 21st century have been described and classified, something that can’t be claimed for any other animal group (except perhaps mammals).
Parrots like Spix’s are peculiarly vulnerable to extinction. At least 12 species have vanished, and another fifty are officially endangered and likely to become extinct in the next few years or decades without – or even despite – the intervention of conservationists. These birds have been let down either by their attractive plumage or their loquacity, condemned to be turned into hat decorations or to life in an aviary. Like orchids (the parrots of the plant world), many parrot species have small, geographically restricted populations and are fussily slow about reproduction – a lethal combination.
Lack of exposure to serious predators over evolutionary time – because they lived on tropical or subtropical oceanic islands – was the downfall of most of Fuller’s birds, and threatens many more. The absence of predators meant that they failed to develop escape behaviours. Some are also flightless, a characteristic which tends to evolve in the absence of ground-dwelling competitors (rodents, for instance, are generally absent from the native fauna of Pacific islands). Other behavioural peculiarities, too, become frailties when population size is reduced, and threaten to tip a species over the brink. The kakapo, a four-kilo ground-dwelling New Zealand parrot whose deep, booming mating call (which can be heard at http://www.bigjude.com/Page8.html) was compared by the late Douglas Adams to the opening bars of a Pink Floyd album, is unique among parrots in having a mating system in which females choose between males gathered together on a common display ground. Now that only fifty wild individuals are left in scattered locations in New Zealand, male displays are often solitary, and females may simply not manage to locate prospective mates. The Mauritius kestrel was probably the rarest bird of prey in the world in the 1970s. This was because of its diet: it lived exclusively on geckos, which were becoming scarce because of the destruction of their island habitat. Parent birds taught their offspring to hunt only geckos, despite the availability of other prey. Conservationists running captive breeding programmes found that baby kestrels were not so fussy, and could be trained to catch a variety of prey. Released from monophagy, the birds have won a reprieve of sorts.
Is the Mauritius kestrel still a Mauritius kestrel if it doesn’t eat only geckos – or is it now in some sense extinct? The boundaries of extinction are not sharply drawn. The giant pied-billed or Atitlan grebe, Podilymbus gigas, which finally disappeared in 1990, is a case of taxonomic but not genetic extinction: the last remaining individuals hybridised with another grebe species, thus preserving some evolutionary history in a new avatar. The sequence of events leading to this semi-extinction was remorseless. The Atitlan grebe was first described in the 1920s, when it was found inhabiting the reedy shores and waters of Lake Atitlan in the highlands of Guatemala. Like other vulnerable birds, it had lost the power of flight. In the 1960s, its population was down to about eighty: the birds’ habitat had been severely reduced first by reed-cutting for the mat-making industry, and next by Pan Am (which in due course also became extinct). The airline had developed the lake as a fishing resort and introduced large-mouthed bass, which ate the crabs and small fish on which the grebes relied. Anne LaBastille, a conservationist, established a small refuge for them on the shore, and the population struggled up to two hundred, only to succumb to further clearing of the reedbeds, this time to make space for lakeside holiday homes. Then an earthquake half-drained the lake, lowering the water level by six metres, effectively isolating the refuge. Finally, the shores were invaded by the grebe’s smaller, flying relative, Podilymbus podiceps, which hybridised with the few remaining giant grebes, producing offspring which flew away – to the surprise of the conservationists who tried to round them up. Giant pied-billed grebe genes are probably still at large in Guatemala, but the species itself is gone. (The extinction of another bird was also hastened by a geological event: the great auk’s last major breeding colony was on Geirfuglasker, an island off the coast of Iceland that sank below the surface in a volcanic convulsion in 1830. The last two recorded individuals were strangled, and their solitary egg broken, by a party of fishermen commissioned by a dealer to collect specimens on the neighbouring island of Eldey 14 years later.)
For every bird in the book, Fuller has tried to find at least one drawing, painting or lithograph: many by the great 19th-century illustrator J.G. Keulemans, a couple (great auk and Himalayan mountain quail) by Edward Lear. He also embellishes the historical account where possible with portraits of the sailors, explorers and naturalists who recorded (and sometimes helped to extinguish) a species and biographical snippets about them – all of which provides an important context for the extinctions themselves. Most of these species vanished, of course, before we had film of sufficient speed for wildlife photography. However, there is a trio of photos of the pink-headed duck of Bengal, which was last seen in the wild in the 1920s: the first shows a pair of birds in captivity in a Surrey park, the next shows just one, and the third is of a stuffed and unmounted specimen lying on its back in the National Museum of Scotland. The most famous photograph of any extinct bird is here, too: Martha, the last passenger pigeon, who died in Cincinnati Zoo at 1.00 p.m. on 1 September 1914 – almost certainly, as Fuller points out, the most precisely pinpointed extinction in natural history.
The rewards of Fuller’s search for contemporary accounts of his subjects are decidedly mixed. In some cases it was evidently a struggle to find anything of significance, the lives and deaths of many species having passed almost unnoticed (which makes it all the more remarkable that Fuller was able to unearth so many pictures). This isn’t surprising, since the recording of natural history had scarcely begun in the 18th century. Then, the primary goal was the collection of new wonders, often accompanied by gratuitous slaughter. Nowadays, there is often a mass of data on population biology, breeding habits and behavioural ecology for bird or mammal species on the verge of extinction; in many cases there are genetic data, too, and in the case of breeding populations in zoos pedigree records compiled according to agreed international standards. When they are extinct – as most of them probably one day will be – we shall know more about these species, and the populations and even individuals that comprised them, than about a great many of the survivors. But for many of Fuller’s birds there is next to nothing. The Liverpool pigeon, known only from a stuffed specimen at the Liverpool Museum in the bequest of the 13th Lord Derby, is a species ‘from an undetermined South Pacific island’. The black-fronted parakeet, also from the South Pacific, ‘was and remains a most mysterious bird’. More desperately, ‘there is very little that can be said about the Marquesas fruit dove.’ And there is what appears to be the first and last recorded encounter with Forster’s dove of Tanna: this bird was collected by Johann Reinhold Forster, a naturalist with Cook on the Resolution, on the island of Tanna in the New Hebrides in 1774 (‘I went ashore, we shot a new pigeon’), painted by his son George, and never seen again.
Like parrots, doves and pigeons seem to have suffered disproportionately more extinctions than other birds, though there is nothing obvious about their biology to explain this. Indeed, two of the most famous pigeon extinctions – the dodo and the passenger pigeon – were of birds that had very little in common. The dodo was doomed for the usual reasons: flightless and insular, it provided easy pickings for sailors, colonists and their attendant invaders (pigs, cats, dogs, rats). This, you could say, was a routine extinction in the course of colonial expansion and human migration to oceanic islands. The last dodo was probably seen in the late 17th century, and all that is left, apart from the many illustrations and descriptions of dubious accuracy, are a few bits of skin and bone, and a head in the Natural History Museum at Oxford. The passenger pigeon, by contrast, appears to have been one of the most abundant birds that ever lived, streaming in vast flocks across North America and nesting in colonies dozens of kilometres across. Its habits and natural history, like those of most other North American birds, were recorded by Audubon, and much more is known about it than about most other extinct birds. The flocks attracted hunting parties of hundreds of gunmen, who blasted the birds out of the sky as they arrived at their nesting grounds. The supply seemed never-ending, but at some point in the 1870s their numbers finally dipped below a critical point, or what modern conservation biologists would call the Minimum Viable Population size. Even though the hunters had by this time lost interest (picking off isolated birds was much less satisfying than mass slaughter), the passenger pigeon was unable to recover, and dwindled to extinction in the wild shortly after 1900 (the last record was of a bird shot in March of that year). Although the total population size in its final decades might have been more than the dodo ever achieved, something about the passenger pigeon’s evolutionary history seemed to require it to live in huge flocks or not at all.
The extinct birds described by Fuller are certainly not the sum total of those which have been wiped out. Many others have probably vanished in the last four hundred years, especially from oceanic islands, leaving no reliable record of their existence. For parrots alone, Fuller lists 14 ‘hypothetical species’ for which no firm evidence exists beyond brief or ambiguous accounts by travellers (by taxonomic convention, a species is not a species unless there is a preserved specimen for reference), and there are many other mysterious species, like the putative white dodo of Réunion. And more birds were certainly hunted to extinction before 1600. For instance, there were between 12 and 20 species of New Zealand moa – giant relatives of the ostrich and emu – all of which disappeared with astonishing rapidity following the arrival of the Polynesian ancestors of the Maoris in the 13th century. Moa remains appear only briefly, if abundantly, in the archeological record of early Maori sites, suggesting that the supply soon ran out. The birds were large, took many years to mature, and laid small clutches of eggs; it appears that their populations soon dropped below the threshold for survival. Although there are reports of two or three moa species still extant when the first Europeans reached New Zealand in 1642, they didn’t last long.
The fate of the moa shows that a human population numbering no more than a few hundred or thousand can rapidly wipe out an entire suite of species inhabiting rugged, forested and generally inhospitable terrain; modern firepower wasn’t a prerequisite. This blitzkrieg has parallels much earlier in the history of human migration, especially into Australia and the New World. Although climate change may also have played a part, there is now strong evidence that many of the largest species of bird and mammal (the so-called Pleistocene megafauna) dwindled to extinction in short order after the arrival of human beings – in Australia about 46,000 years ago, in the Americas from about 14,000 years ago. The Australian extinctions included another giant moa relative, Genyornis, one of the largest birds ever to have lived. These prehistoric extinctions leave their ghosts: the peculiar divaricate shrubs of New Zealand, whose leaves are carried inside a canopy of twigs, apparently to protect them against browsing by moas, or the large seeds of some of the tree species of Central American forests, once carried to new sites in the guts of megaherbivores, but now too big to be dispersed. Ecological ghosts abound also in Hawaii, where 40 of the original native bird species are extinct, and many of the rest on the verge of being so. This small island group alone accounts for nearly half the extinctions recorded in Fuller’s book. One family of birds, the Hawaiian honeycreepers, originally numbered at least 41 species; now 13 of these, maybe more, are extinct, and of the remainder only three are not endangered. With losses like these, entire ecosystems become disjointed and even more prone to invasion by exotic species.
On land, human-induced extinction has proceeded in three phases. First, there were the megafaunal extinctions in the wake of migrations to previously uninhabited continents; next, the island extinctions and extinctions through overexploitation (the bulk of those recorded here); and finally, the continental and global-scale extinctions that we are now poised to inflict through habitat destruction and fragmentation, introduced species and climate change, extending the Hawaiian experience to the rest of the world. In marine habitats, new evidence indicates that overexploitation has been a major engine of change for centuries, or possibly millennia, such that no coastal waters in any part of the world are in anything like their pre-human state. Few biologists now doubt that we are already embarked on a new mass extinction, which will result in the loss of a large fraction of species from the world’s biota. The rate of loss is estimated at more than a hundred times the natural ‘background’ extinction rate calculated from the fossil record, which shows, crudely, that the average life of a species is between five and ten million years.
Mass extinctions have happened before, and define some of the major boundaries in the geological and evolutionary history of the earth. What is different about today’s mass extinction is that it is clearly being brought about by a single species. The five previous ones, as far as can be judged, were all caused by physical events, the most famous being the impact of a huge meteorite in Mexico 65 million years ago, which induced immediate climate change and did for the dinosaurs and much else besides. Conservationists, who are focusing more and more on maintaining wildlife in human-dominated landscapes, are now having to cope with the real and predicted effects of climate change, which may well cause the optimum conditions for individual species and entire ecosystems to shift wholesale by hundreds of miles or vanish altogether. In circumstances like these, the rewards in terms of species saved will be all too few.