Michael McCarthy: Lord God Bird is what dreams are made of

I went birdwatching in Washington last week. You'd normally go to the District of Colombia to gaze upon power and its trappings – the splendid public monuments, the President's helicopter clattering off from the White House lawn – but one corner of the US capital is remarkable for its avifauna: Rock Creek Park.

Rock Creek is a stream which originates in Maryland and flows down to join the Potomac, Washington's own great river, through the city itself. It forms the boundary between the downtown area and the smart suburb of Georgetown. For much of its length the river's wooded valley is barely 100 yards across, but north of the city centre it broadens out to a belt of deciduous forest about a mile wide. Nothing like it in London.

I went there to talk to the Rock Creek birders, men and women who gather in the park every morning at 7am (it's a long story: I was researching a book). The birders were fascinating – a nuclear physicist, a neurology professor, a classical guitarist – but the unfamiliar birds excited me even more, Acadian flycatchers, ovenbirds, various warblers, and most of all, a pileated woodpecker. This is a monstrous great thing: its dagger-like black, white and scarlet head makes you think of a pterodactyl. But even more gripping is that it is the closest living relative to its even bigger cousin, the ivory-billed woodpecker, which is extinct. Or is it?

In 2005 a group of senior US ornithologists made the sensational claim, in a paper published in Science, that they had rediscovered America's most legendary bird in a remote corner of Arkansas. Their evidence is far from conclusive: the supporting video is fuzzy in the extreme, and many scientists have since claimed it shows not an ivory-bill, but a pileated (the species are fairly similar). Others remain convinced that the ivory-bill is still out there, deep in the backwoods.

There is a powerful need to believe it; huge and spectacular, this mysterious creature is the stuff of dreams. (It was known as the Lord God Bird, from the expression people uttered on first glimpsing it). I think part of what made seeing the pileated woodpecker so special was what you might call, even if at one remove, an ivory bill thrill.

Hovering high above the rest

The richness of America's bird life (600-plus species against our 200-plus) was impressed upon me as I sat overlooking a suburban Washington garden – a backyard, in America. The highlight of a stunning assemblage of goldfinches, chickadees, mourning doves, nuthatches, cardinals, song sparrows and woodpeckers (three species) was a female ruby-throated hummingbird, above. Watch it hover and your eyes widen. Watch it fly backwards and you shake your head in disbelief.