On a wing and a prayer

A couple of days before the Euro 2004 final in July, another football match - this one played by two Portuguese teams - took place 700 miles off the coast of Portugal in the middle of the Atlantic Ocean. The players were scientists, conservationists and local government officials and their goal was to save a very rare bird from extinction on the remote islands of the Azores.

A couple of days before the Euro 2004 final in July, another football match - this one played by two Portuguese teams - took place 700 miles off the coast of Portugal in the middle of the Atlantic Ocean. The players were scientists, conservationists and local government officials and their goal was to save a very rare bird from extinction on the remote islands of the Azores.

The Azores bullfinch is one of Europe's most endangered birds. Once abundant, there are now just 120 pairs left and confined to a tiny fragment of mountain forest on a single Azorean island, Sao Miguel. Standing on the rim of an extinct volcano looking down on to a patch of forest just 500 hectares in extent, it was hard to believe that I was looking at the total geographic range of the Azores bullfinch. Oceanic islands typically have few land birds, and the Azores bullfinch is just one of only 15 bird species on Sao Miguel. Island populations are also vulnerable.

Indeed, the vast majority of the world's birds that have become extinct in the last century were those that occupied oceanic islands. The problem is that should a catastrophe occur such as a hurricane, an earthquake or volcanic eruption (all of which are possible in the Azores) there is nowhere to go. The smaller the bird population and the larger the catastrophe, the more likely it is that extinction will occur. Few species are more vulnerable than the Azores bullfinch.

Beautiful but bizarre, the Azores landscape could be Scotland. The rain, wind and fog feel distinctly Scottish, but it's warm enough for locals to grow bananas in their backyards. The islands are volcanic and were never attached to mainland Europe, so the breeding bird species - which include the robin, blackbird, chaffinch and the bullfinch - all got there under their own steam some time in the past million years.

Surprisingly, they all came from northern Europe rather than the Iberian peninsula, which is considerably closer as the bullfinch flies. How did the birds get there and how were their populations established? Think about it. The Azores erupted from the seafloor and initially, of course, were uninhabited by anything. Once the lava had cooled and plants became established the odd bird arrived, blown way off its normal migration route. If there was something appropriate to eat it might survive, but only if there were others of the opposite sex was there any chance of starting a new population.

Even if by some lucky chance a male and female arrived together, the likelihood of starting a new viable population would be slim, for after a few generations inbreeding and the accumulation of deleterious mutations would catch up and probably extinguish them. Since there is no obvious sign of inbreeding in the current population, the most likely scenario is that a small group of European bullfinches arrived together. They probably came from northern Europe since these are the only European bullfinches that do much migrating and because they are closer to the Azores bullfinch in size.

No one knows when the bullfinch arrived. Records from a cleric who documented the islands' natural resources for the Portuguese government in the 1500s soon after the first people arrived, make it clear not only that the bird was present but that it was also abundant. The Azores bullfinch is now sufficiently distinct from its European cousin to be considered a separate species so it probably arrived tens of thousands of years ago. The aim of on-going research into the bullfinch's DNA is to allow researchers to pinpoint the birds' arrival time precisely.

The most striking feature that distinguishes the Azores bullfinch from its mainland counterpart is that it is sexually monomorphic - males and females look the same. Through binoculars, or even when viewed close-up in the hand, the sexes are very hard to tell apart. In contrast, the European bullfinch shows a pronounced sex difference in its plumage. The male has a deep rose-pink breast, while the female has a pinkish-brown breast. In the Azores bullfinch, male and female look like female European bullfinches: a subtle blend of pinkish brown with glossy blue-black trim.

It is generally assumed that the reason male birds are brighter (or more vocal) than females is due to sexual selection. This is Darwin's idea, and he thought that brighter males may be either better at intimidating other males in contests over females, or (more likely) they are more appealing to females. Subsequent experiments with different bird species in captivity show that in most cases females much prefer males with brightly coloured plumage.

So why should the male Azores bullfinch have lost its main marriage attribute? We don't know. But the fact is that many bird species on islands are less sexually dimorphic than their nearest mainland relatives. Possibly the smaller populations on islands make female choice less likely, or less necessary. Another idea, as yet untested, is that the food substances needed to make the male bullfinch's pink breast are missing from the Azores. Many red birds rely on pigments called carotenoids, which occur naturally in some plants, to generate red- or yellow-coloured plumage. A flock of yellow canaries released on Midway Atoll in the Hawaiian archipelago in 1909 by the wife of the governor there turned white at their next moult precisely because there were no carotenoid-bearing plants. Later, as more and more plants were accidentally or deliberately introduced to Hawaii, a daisy-like flower containing carotenoids was among them, and the canaries went back to being yellow - they still are.

Whether or not the Azores lack some crucial carotenoids by which the male bullfinches could enhance their beauty is unknown.

All bullfinch species, and there are seven of them around the world, are strict vegetarians, specialising in the buds of trees, especially fruit trees. Since the Middle Ages, the European bullfinch has been considered a pest to apple and cherry orchards, and in the past were killed in their thousands for their destructive feeding habits.

In the early 1990s the Azores bullfinch made itself unpopular by feeding on the blossom of orange trees that the locals had planted and it was sufficiently numerous to be considered a pest. Now, however, there are few orange trees left on Sao Miguel for the Azores bullfinch to plunder.

Indeed, there is precious little for it to feed on at all. And this is the problem. The shortage of natural food for the Azores bullfinches is clear - nowhere else in the world do bullfinches eat fern leaves or the spore-filled fruiting bodies of ferns, both of which are likely to constitute a poor-quality diet. A huge reduction in the birds' natural habitat means that without some kind of intervention it will be starved out of existence.

Here is the problem. During the 1940s, in an effort to provide employment and boost the economy, the Portuguese government decided to clear the native forest and replace it with the fast-growing Japanese cedar. For 40 years the native laurels and hollies on whose nutritious buds the Azores bullfinch depended, were felled and replaced by an impenetrable, inedible covering of cedars. To add insult to injury, destroying the native trees allowed alien plants, such as the rampant Himalayan ginger, to invade and effectively smother the birds' natural food supplies. As the alien plants continue to spread, bullfinch numbers continue to fall.

One year ago a committed team of enlightened conservationists and ornithologists launched a last-ditch attempt to halt the decline. In a hugely ambitious EU-Life project, the alien plants are being removed and replaced with native species. In some cases the cutting and replanting of native trees is being done by the very same forest workers who 20 years previously did the opposite. This is no trivial task - the forest slopes are steep, soggy and dangerous. The aim is to recreate 300 hectares of native forest in which the birds can maintain a secure foothold.

Football matches can be replayed during time off, and in the grand scheme of things it matters little who wins or loses. Saving an endangered species isn't a game. This may be the birds' only chance.

Professor Tim Birkhead has recently been made a Fellow of the Royal Society. His latest book, 'The Red Canary', is published by Weidenfeld & Nicolson