🇬🇧 Compass and Cryptochromes
I - A nest of robins
1294. Yesteryear, a mild and early summer,
Flowerboxes in bloom on the facade;
Right under my study window
A box of new pelargonias.
I was just feeling the plants
My fingers around the roots,
Because it feels good, and then:
Suddenly something alive, downy,
Pulsating and warm to the touch
Hidden in there: a robin’s nest.
1295. I confess, I had seen something,
When I stood by the window:
A quick flicker, a brown shadow,
Perhaps af flapping of wings,
So, I did know something was there,
No, someone; but a nest?
It didn’t occur to me,
Even if it should have;
Dolus eventualis, they say:
Throw that match, give that shrug;
Mess around that flowerbox, so what?
Let happen that which happens.
1296. Robin chicks, four, five of them,
Scuttled away in panic,
Dropped from the ledge to the ground,
Spread out into hiding, disappeared.
The robin mother calling,
Plaintive, I assume, desperate,
I should think; and me, careless,
Destroyed that years brood;
Clumsy, stupid, culpable.
II - Trek south
1297. Only a third would survive
The first trek to North Africa
And the flight back here again:
Shot by hunters, fleeced by crows,
Poisoned by peasants, eaten by cats,
Gobled by owls, smashed by machines,
Dead from exhaustion and lost,
Diverted by radio frequencies,
Lethal traps of light pollution,
Glass facades and glittering cities,
Robbed of food and resting places;
Every year billions perish.
But still, some of them survive
The first trek, now more experienced,
With landscapes, contours and
The highlights of the route etched
In their one-gram brains.
1298. With thanks to robins
We now know, roughly,
After ten thousand years,
How birds navigate the globe.
The answer is magnificent, I think,
Like also the science,
The imagination, the inventiveness
That made it possible;
In short, all that empathy,
That makes wonder into science,
And science into poetry.
III - The navigation of birds
1299. Birds, all of them apparently,
Can navigate around the globe
On the earths' geomagnetic fields.
They sense direction and position
By picturing the geomagnetic field
With an accuracy of a few inches
Across thousands of miles.
1300. Robins have been studied
For more than half a century;
Enclosed in cages and containers,
Turned, rattled and moved,
Radiated with magnetic fields,
Subjected to illumination in
Blue, yellow, green and red.
Blindfolded, anaesthesised,
Exposed to radio waves,
Magnets upended north and south
But robins didn’t care,
Tissue samples extracted,
Stacks of biochemical diagrams.
This is what they found:
1301. Robins have a sense, more than one,
That perceives geomagnetism,
An extremely weak impuls of energy,
Many millions times less
Than it was thought possible
To detect with organic senses;
But it is certain that they can.
1302. Studies shows that the “compass” of robins
Has no north-south polarity
As the human technical compass;
A self-projecting concept
About other animals’ sence of direction.
No, robins perceive the inclination
Of the geomagnetic waves
From pole to geomagnetic equator;
It’s an inclination compass!
Robins perceive the angle
Of the geomagnetic waves
Bearing towards or away from
The magnetic equator,
Where the angle is zero.
Thus, the robins know
In which direction to fly.
1303. Robins can also detect
The strength of the magnetic field,
Which is strongest at the poles
And weakest at the equator,
Infinitely weak, in fact,
Measured in mili- or microtesla,
Weaker that the magnetism
Under a high voltage cable,
Weaker than the murmur of electrons
In the body of the bird itself.
1304. By knowing magnetic intensity
Robins can find their position
Along a north-south axis.
Jointly with the other compass -
The inclination of magnetic waves,
Which indicates direction -
Bird can perceive something close
To a latitude and longitude.
1305. Where there is external stimuli,
There needs be a receiver.
Hence, for years, they looked
For the robins' magneto-receptors;
What are they, where are they, and
How do they work?
IV - Cryptochromes
1306. From quantum mechanics is known
A phenomenon called radical pairs:
Two molecules exchange electrons
And thus change their electrical charge.
When a radical pair is formed
The molecuels begin to spin,
Either in parallel or opposite.
Thus, two electrical states occur:
State at rest and state of signal.
A radical pair changes states
Millions of times in microseconds.
The spin, we now know, is affected
By the geomagnetic field.
1307. Researchers formulated af theory
An epiphany, in fact, in the ‘80s,
That radical pairs are the key
To robins’ geomagnetic sense:
And because the radical pair
Requires light to be formed,
It must be in the eye of the bird.
1308. In the year 2000 researchers proposed
That the receptor is a molecule
In the eye of the robin and other birds.
This protein, called a cryptochrome,
Forms radical pairs in a spin
When hit by rays of light.
The theory holds that magnetic waves
Affects the spin of the radical pair
In parallel and opposite directions.
The spin creates electrical impulses,
That send on-off signals to
A biochemical signalling function,
Which can be seen as a “lever”
On the outside of the cryptochrome.
1309. Cryptochromes occur in birds eyes
At the tip of the optical rods.
As the cryptochromes spread
Across the arch of the retina
The bird can “see” the direction
Of incoming magnetic waves.
In the same way that animals and birds
Detect direction with a pair of ears.
1310. Researchers have explained biochemically
How radical pairs in the cryptochromes
Fire off neuro-transmitted impulses
To the optical centres in the birdbrain.
There, we must believe, the robin,
In a way that we might never know,
Is able to “see” the earth's magnetic field;
This “vision” or this “image” or
This sensory perception is a “map”
That the bird will need
To find its way, to know the route;
A “map” in the form of light? shapes?
Pixellated fields? Wavy lines?
A “map” that fits the “compass”:
Memorised routes, main landmarks
Or something quite different; spectres of light,
Ultraviolet or infrared, or maybe
Magnetic properties in the landscape.
Everything is possible.
1311. Birds have developed other senses
For use in their navigation:
The beaks of birds contain magnetite,
The most magnetic mineral known.
Biochemical processes in the beak
Sends neuro-transmitted signals
To part of the bird’s brainstem;
Here, maybe, is the neurologial path
To sensing geomagnetic intensity.
1312. For certain, birds also use vision,
Smell, memory, experience,
Mountains, seas, coastlines,
Maybe sound, temperature, wind,
Maybe a fifth or sixth method
Of sensing place and direction.
V. A larger world
1313. A new insight, a larger world,
That will become as natural
To my children and grandchildren,
As the the "compass needle" of birds
Was to me, when, as a boy
I watched the swallows leave.
1314. To a brood of robin chicks
Endowed with global gifts
They never lived to use;
Inadvertently destroyed,
Stroeby Beach, summer of 2022.
In memory.
During the past 75 years, a large number of researchers have contributed to the accumulated knowledge on the navigation of birds using the earth's geomagnetic field. It is impossible for me to mention them all here; but let me point to a few whose articles have been a gift for me to read: Klaus Schulten, Thorsten Ritz, Henrik Mouritsen, Peter Hore, W. Wiltschko, R. Wiltschko.
Ed Yong An Immense World (2022) is a superb introduction to the sensory perceptions of living beings and I warmly recommend it to everyone. The book's chapter on the ability of birds for optical navigation using the earth's geomagnetic field furnished me with knowledge and inspiration for the poem above.
New in Index Ten Thousand:
Robin's nest ◦ 1294, Flowerbox ◦ 1295, Brood ◦ 1296, Cat: domestic ◦ 1297, Light pollution ◦ 1297, Robin ◦ 1298, Science ◦ 1298, Earth's geomagnetic field ◦ 1299, Radio waves ◦ 1300, Impulse ◦ 1301, Equator ◦ 1302, Electron ◦ 1303, Compass ◦ 1304, Magneto-receptor ◦ 1305, Radical pair ◦ 1306, Electrical charge ◦ 1306, Geomagnetic sense ◦ 1307, Chryptochrome ◦ 1308, Magnetic waves ◦ 1308, Rods: eye ◦ 1309, Landmarks ◦ 1310, Visual centre ◦ 1310, Navigation ◦ 1311, Sense of direction ◦ 1312, A larger world ◦ 1313, Gifts ◦ 1314.
