Intense experiences of the soul are by their nature uncommon. Perhaps the one about which there has been the greatest speculation, historically, was that of initiation into the Eleusinian Mysteries, the most elevated religious rites of ancient Greece, held at Eleusis, west of Athens, for more than 1,000 years, until in the 4th century AD the Roman Empire became Christian, and boring, and banned them.
No one knows exactly what happened at Eleusis, because participants in the mysteries all took a vow of secrecy. But we know they were based on the cult of Demeter, the goddess of the harvest and fertility – of the cycle of death and rebirth, if you like – and it is clear that those who did take part, who included some of the greatest minds of Greece and Rome, experienced an intensely heightened spiritual state. (There has been conjecture that it was brought about with the aid of hallucinogenic mushrooms.) Whether it was a sense of being born again, whether it was a sense of communion with the divine, we do not know. All we know is how intense it was.
I have been thinking about Eleusis because I have been casting around to find something with which to compare the most intense experience I know of in the natural world, which is nightingale song, heard at night. Of course, comparing the noise made by a small brown songbird with a major religious festival is not really appropriate. Indeed it's probably way over the top; the trouble is, I cannot think of anything else to try to get across quite how exceptional a nightingale encounter can be.
I'm talking about fairly special circumstances, I admit. You can hear a nightingale during the day – yes, they are diurnal too – on a country walk, say, and not be moved one jot; unless you know it, you may not pick it out from the general birdsong background. Once you do know it, though, you realise that even in the daytime, nightingale song is different. A combination of rattling whistles and long, melodious notes, it is extraordinarily loud, probably the loudest of any songbird; it is also extraordinarily sustained, sometimes seeming to meander on without end.
But it is in the dark that it comes into its own. It usually brings with it a theatrical context: to be in a position to hear it properly, for example, you may well find yourself deep in a wood at midnight, somewhere you would not normally dream of going, where ancient fears creep out and set up a living tension. A wood at midnight is an unworldly place of unfathomable and intimidating shadows; it is a remarkably dramatic stage on which to hear a songbird perform. And when it does perform, if you are really close to it, its voice fills the whole dark world. It takes over everything; in the blackness you can see nothing, you can hear nothing else. All there is in existence is this blazing song, which seems to be performing a duet with silence. Silence moulds it; silence defines it; it is the silence of the night all about you which lets it fill the world with sound.
If you can ever experience this in a midnight woodland – I've experienced it three times – it touches and lets loose something in you, something in the soul, which is enormous, yet hard to name. I would use the word ecstasy, but that's not quite it. Whatever it is, you suddenly see why this of all songbirds has been celebrated in literature for thousands of years; you understand what it was that fired up John Keats so furiously, and drove him to write the most notable ode in English.
But it's not there long. Nightingales sing only for a short period of about six weeks in the breeding season in April and May, when they return to Britain from their winter quarters in West Africa, as they are doing right now. (The peak of their arrivals will probably be next weekend.)
It is exclusively the male birds who sing, in order to attract mates; as soon as a male finds a female and pairs up with her, he falls silent.
These, then, coming up, are the nightingale weeks of the year.
Unfortunately, it is growing ever harder to hear the bird; numbers have dropped by more than 90 per cent in the last 40 years, so for every 10 nightingales that were singing in Britain when Paul McCartney announced the break-up of the Beatles in April 1970, only one is singing now. The species is retreating steadily towards Britain's bottom right-hand corner, the extreme south-east, and is now confined to the area below a line drawn from The Wash to The Severn, with its strongholds in the Home Counties and East Anglia.
But if you are lucky, over the next six weeks – if you know someone who knows where a nightingale is, and knows the wood where it is singing, and will lead you there at dead of night – take the protective cover off your soul, leave it bare. Let it feel to the full the most singular and spine-tingling moments Nature can offer.
... and this is your chance to hear it
As listening to nightingales is not easy, we are offering a helping hand. To hear soundclips of the nightingale's song, click on the links below. It may not be quite the same as listening in a moonlit woodland, but try listening in a quiet room, with your eyes closed.