Migrating birds are "a beating layer in the atmosphere, a living coat for the planet"

Nicolson's new book - entertaining and full of  fresh and important ideas

"THE migrating impulse gives birds a glamour that we, in our rooted repetitive habits, spending 30 years or more walking the same paths, can never have."

So writes Adam Nicolson in his latest book Bird School - A Beginner in The Wood.  

It is a most absorbing volume, not least the section  on migration where he brings us up-to-date on the latest research on  a phenomenon that sometimes involves as many as 50 billion birds flying from one clime to another - in effect "another beating layer in the atmosphere, a living coat for the planet".

He says birds live "within the grid of a magnetic world - the root of their inherited direction finding ability".

Highly responsive molecules in the retina can detect variations in earth's magnetic field, transmitting the information to their brains via the optic nerve.

Daylight, suggests Nicolson, drowns out subtle magnetic signals which is why many migrants fly after dark.

"They need a small amount of light but not too much for the magnetic compass to work," he writes. "What they need, in effect, is starlight -  blue light."

The author is good in acknowledging the sources of his research except with his assertion that migration mostly occurs "high, often at four thousand feet, sometimes up to thirty thousand feet".

This observation will doubtless be welcomed by the wind energy  industry, but is it not too much of a generalisation?

Depending on other factors, notably the weather, birds fly at various levels - sometimes just over the surface of the sea. 

This excellent book contains fascinating theories about the many facets of birdsong - for instance, a challenge to the long-held belief that one of its purposes is to mark out a territory.

He refers to a paper by the Belgian philosopher Vinciane Despret indicating that song is basically an act of self-expression.

Writes Nicolson: "For her, territory is not a possession but a performance in the theatre of self".

The book includes an interesting table on the exact number of minutes before sunrise at which different birds start to sing.

The earliest tend to be Song Thrush,  Blackbird and Robin, while the latest are often Chaffinch, Blue Tit and Chiffchaff. 

Why so? 

"The bigger a bird's eyes, the earlier it can detect the light and so the earlier it starts to sing," suggests Nicolson.

He further notes: "It may be that pre-sunrise dawn is light enough to sing but not light enough to look for food.

"Dawn gets the necessary singing out of the way before  the daylight of foraging can begin."

Almost inevitably the subject of song draws Nicolson to investigate  ways in which it inspired composers such as Debussy, Ravel and particularly Beethoven who, like him, particularly cherished the "blackcurrant liquid" song of the Blackbird.

This is all fascinating stuff as is the author's foray into how some of the world's greatest poetry has been inspired by birdsong and the ways in which individual poets have mined it to shape their verse.

He particularly admires John Clare's poem about the Nightingale for the ways in which its language and rhythm echo the song of the bird,  but he is less appreciative of the better-known poem about the same species by John Keats.

"It is obvious Keats was no naturalist," he writes. "There is some suggestion he might have been listening not to a Nightingale but to a Song Thrush."

What a putdown! 

Generously illustrated, Bird School - A Beginner in The Wood is published at £22 in hardback by William Collins.