What do you think is the holy grail of wildlife watching? For some people undoubtedly it would be the big beasts of Africa, whereas others might say the great whales, or polar bears, or a tiger in the wild. Me, I've long held more modest ambitions: I've never seen a hawfinch.
The hawfinch is the nearest thing in Britain we have to a parrot (apart from the several real parrot species now breeding here, but that's another story); a bold-looking, pinkish-brown creature with a big bill and a fantastic scientific name, Cocothraustes cocothraustes, which has always seemed to me the bird equivalent of Humbert Humbert, or Major Major Major.
Anyway, I've never seen one, in spite of trying, and had you asked me a week ago what my own wildlife holy grail was, I suppose hawfinch was the word, being a bit of a sad geezer, which I might have come out with. But not any more.
For the past fortnight I have been in Mexico covering the UN climate change negotiations in Cancun, a 15-mile strip of colossal luxury hotels on the edge of the impossibly blue Caribbean, with the conference taking place in one of the most opulent of all, the Moon Palace, which flaunts at its entrance a giant statue of a naked woman throwing her head and arms back so that her giant breasts are pointing vertically at the sky, which can only be described, using initial capitals, as Truly Ghastly.
But there are compensations. The Tropic of Cancer is a long way north: on the coast of the Yucatan peninsula we are in the tropics here, with flame-coloured tanagers (they're birds) and giant cobalt-blue morpho butterflies fluttering around the hotel grounds, and I spent the first week of briefings and draft texts longing for a real taste of tropical wildlife which finally, last weekend, I was able to satisfy.
I went to Sian Ka'an, a national park 80 miles to the south: it covers no less than 1.6 million acres and thus protects an immense pristine area of Yucatan coastline, lakes and forest, as well as ancient sites of the Maya, one of Mexico's pre-Columbian peoples, from the ambitions of the hotel developers of Cancun, expanding steadily southwards. (Designating it has been a most enlightened decision of the Mexican government.)
In Sian Ka'an I tagged along with a Mexican birder called Hernando, and we had a local Maya guide called Ismael, and we saw sensational birds, such as a keel-billed toucan, an ocelated turkey, a tawny-winged woodcreeper, a savannah vulture and a black-headed trogon, as well as some of the beautiful North American warblers which are here for the winter. Even Hernando, who has seen 850 of Mexico's 1,153 bird species, got very excited because Ismael produced for us a bird he, Hernando, had never seen – a "lifer" in birderspeak – a Mexican ant-thrush, which Ismael brought out of the forest by imitating its call.
When we had finished I asked Hernando what his favourite Mexican bird was. He looked at me as if surprised and threw up his hands. "The quetzal, of course!" he said. "The what?" I said. "The resplendent quetzal!" he thundered, and grabbing my Mexican field guide, he found the colour plate: there at the top left-hand corner was a brilliant green bird with a red breast, about the size of a jackdaw.
It was certainly handsome, but what was remarkable was the iridescent green tail, which stretched down the whole length of the page, past the paintings of 37 other birds, to the bottom: it was five or six times the length of the bird itself. It was so long it seemed scarcely credible that it could fly (but it does). The American ornithologist Roger Tory Peterson described it as "the most spectacular bird in the New World".
But it was more than that, I discovered. The resplendent quetzal was the sacred bird of the Maya, and as I read up about it, I found it was the sacred bird of the Aztecs, too, further north: they associated the quetzal with Quetzalcoatl, their feathered snake-god. In fact it was considered divine across all of pre-Columbian Central America, a legendary creature; and it maintains its legendary status still.
And yet it was real. Most legendary birds, such as the phoenix, or theroc (the giant Asian bird of prey supposed to be able to carry off elephants) are purely mythological, yet here was one which you could actually go and see, as long as you were prepared to trek up into the cloud forests of southern Mexico, Guatemala, or Costa Rica.
And there and then I conceived a passionate desire to do that, and to set eyes on the resplendent quetzal before I die, which suddenly seemed a holy grail of wildlife-watching which was truly worthy of the name.
I don't know if I'll ever do it, but – if you can understand this – I somehow feel that merely conceiving the ambition is worthwhile in itself, as if it has made me a little bit less of a sad geezer; as if anyone who seeks the quetzal is somehow themselves sprinkled with a few grains of the iridescent green dust of its legend. So I carry within me now a newfound aspiration containing a distant vision of cloud forests, although, and I want to stress this, I by no means look down on the old one, and if you offer me the chance to see a hawfinch, I won't turn you down.