Extinction

Extinction of species is as natural a part of evolution as is speciation. The process of Darwinian natural selection may generate species which are highly adapted to a particular prevailing set of environmental circumstances. The posh name for "highly adapted" is stenoecious. The problem with these highly adapted species is that they "paint themselves into a corner", and if the environmental circumstances happen to change, they are stuffed (Ooops, I mean unable to cope with the changing circumstances). So "adapted" is the opposite of "adaptable" (for those who want to know, "adaptable" species are euryoecious).

My favourite example of a stenoecious species is the Everglade Snail Kite, a critically endangered species, which I have been fortunate enough to see in the Everglades National Park in Florida.

The Everglades Snail Kite - adapted to eat only aquatic snails

This bird is so highly specialised that its bill is critically structured only to winkle out the flesh of an aquatic snail called the Apple Snail. It is superb above all others in locating, catching and eating Apple Snails.

The aquatic Apple Snail - exclusive diet of the Snail Kite

So, from a conservation point of view, if the authorities in Florida wish to increase the flow of drinking water to Miami; or divert the flow of the Shark River into agriculture; or manage some of the Everglades in the interests of the Seminole Indian Tribe, then this destroys the habitat of the Apple Snail. The Snail Kite, whose bill is adapted to dealing exclusively with a diet of Apple Snails, suffers a knock-on in the food chain. If the snail becomes extinct, the kite inevitably follows.

The concern that conservationists feel now is the rate of extinctions . Research reveals that until the 18th century, an average of about 0.25 species became extinct per year. This rate jumped to one species per year in the 19th century, to 1,000 species per year in 1975, and to 40,000 species per year by around the year 2000.

So what has caused this alarming increase in the rate of extinction of species in recent decades? It would be perverse indeed to imagine that man's activities had nothing to do with it. Extinction can be caused by direct hunting: the Dodo, Passenger Pigeon and Stella's Sea Cow are well-known examples.

The Dodo - too nutritious for its own good?

Indirect human affects such as habitat destruction (e.g. tropical rain forests), wetland drainage, pollution and climate change have all taken their toll. However, one of the most important causes of extinction is the most catastrophic, and also the most pitiful because it could have been avoided with foresight. And that is: the introduction of alien species.

In a balanced ecosystem, the eponymous "balance of nature" is in harmony of sorts. There is a complex interacting dependency that maintains a long-term stability. Species become extinct as circumstances change naturally, to be replaced by others that evolve to capitalise on the new situation. But to introduce an alien from a different ecosystem can cause chaos. The places where these affects are most devastating are island archipelagos which became geologically separated early in evolutionary history: Australia, New Zealand, Hawaii and the Galapagos are classical examples.

Australia separated by plate tectonic movement from the super-continent of Gondwanaland many centuries ago. At the time, mammals were at an early stage of evolution, and a separate line, the marsupials, developed in Australia. They became isolated from the mainstream of mammal evolution where the more advanced and "successful" placentals evolved. When Australia became settled by European people, a few placental rabbits were introduced and they were able to out-compete the endemic herbivores and, axiomatically, "bred like rabbits" and virtually took over the continent. In desperation, European foxes were introduced to control the rabbits. Did that work? Oh no, the foxes turned to predate the indigenous marsupials that were not adapted to avoid such predators. There were many extinctions, and many species, including the Leadbetter's Possum, have become endangered.

Leadbetter's Possum, endangered emblem of Victoria, Australia

In New Zealand the position is arguably even worse. This land-mass separated off from Gondwanaland even before Australia, in a period before any sort of mammal evolutionary line had commenced. In isolation, the higher animals in New Zealand were restricted to birds, reptiles, fish and amphibia; but no mammals. (Seals and bats found their way independently in due course). Without the need to escape from mammalian predators, many endemic bird species in New Zealand became flightless, or developed greatly weakened flight. Obviously, the Kiwi is the best known example, however there are dozens of other examples.

As in the case of Australia, the introduction of a few rabbits into New Zealand wreaked havoc. And the response to attempt to control the rabbits? Introduce cats, ferrets, weasels and stoats! The rest, as they say, is history. These advanced mammalian predators ignored the rabbits and took readily to the flightless or weakly-flying bird species. One of the alleged fastest extinctions on record occurred when the lighthouse keeper on Stephen's Island let his cat out, which cleaned up the entire population of the unique Stephen's Island Wren in a couple of hours!

I count myself fortunate to have lived in New Zealand during the 1970s. As a birdwatcher, I was astonished at how much the bird life was dominated by introduced species; the European Blackbird, Yellowhammer, Redpoll, Skylark, the Indian Mynah, to name but a few. To see the interesting endemics required excursions into the thickest parts of the forested National Parks, or even to the off-lying islands where the Wildlife Service had eradicated alien predators. High on my list to see was, of course, the Kiwi, and I was able to locate a few of these as they pecked about on the high-tide mark on a beach at night on Stewart Island.

Flightless Spotted Kiwi of New Zealand

Another rare endemic bird that fascinated me was the Kokako. This had two sub-species inhibiting the North and South Islands, respectively. The North Island sub-species was rare but secure, but the South Island race was precarious. And it was sad to learn from Ju's Little Sister that it has recently been declared extinct.

The North Island Kokako is a shy, secretive weakly flying forest dwelling species. To see one simply "flying about" is extremely unlikely. But there are more subtle methods: being territorial, the males respond very well to tape recordings of the song of their own species. Males regard the recording as a rival intruder and will sometimes emerge to see him off!

And so it was with a tape-recording of a Kokako supplied by the New Zealand Wildlife Service, and a tape player system that would look cumbersome by today's standards, I set off to camp by the shores of Lake Okataina (not far from Rotorua) in the heart of Kokako country. I set my alarm for an hour before first light, and enthusiastically drove to a likely looking spot in the forest and started playing the tape at dawn. You can imagine my excitement when I heard a bird singing the mellifluous fluty notes in response! I remember tingles down my spine, and the hairs standing up on the back of my neck!

But would the bird come out and show itself? No way! By the time the rising sun was casting shadows, the birds had shut up shop and were refusing to play!

The second morning, it was harder to get out of my warm sleeping bag - there were ground frosts even in spring. However, I returned to the same spot, and started playing the tape again and sure enough, the local male responded! Surely, I felt, he would show himself today! And just as I sensed he was getting close, the song from my recorder started deepening in tone, and slowing down. Damn! The batteries were flat! I gave up and went straight to the nearest service station for a new set of batteries!

On the third and final morning, I was suffering from severe sleep deprivation. As the alarm dragged me from the depths of slumber, and the sweetest of dreams, I tried every trick in the book to persuade myself that there was no point; I thought of every excuse why it was futile to try, why I needed another hour's sleep (at least!). But operating on automatic pilot, I dragged myself from the comfort of the sleeping bag and made my way again to the now familiar spot. Would it work this time? Well, yes it did. It was not the best view I have ever had of a bird, I must admit. But it did show itself, briefly, as it hopped along a leafless branch, and then dropped back into the canopy and disappeard from sight. There it was - the Kokako!

New Zealand North Island Kokako - rare, but thankfully well protected