Migration #3  Summary - March

All Hard Work and No Help

Taken as a whole, March has not been a good month for migrants. The airstream over western Europe / British Isles has been consistently from the east or north-east, and only a few days where the winds dropped to light airs or local calms. Checking the records back to the start of the month, I find that there has not been one single 24-hour period where the birds would have wind at their backs for flying. And over all this, of course, the inescapable, unrelenting cold...

… it's no wonder that I haven't seen a single swallow yet, here in the North.

Geostrophic Wind Scale for 30.3.13 (Click for larger image)

April starts with the mixture as before. Although daytime temperatures will improve during week one, this will only be by a few degrees. The problem remains the same: “blocking” anticyclones (high pressure) over Scandinavia and central Europe will keep the usual progression of Atlantic weather systems at bay. Towards the middle of the month we should see a change towards more typical spring conditions, but average temperatures will remain on the low side of normal.

All this makes it tough work for our UK birds to reach their summer breeding sites. Even the strong fliers, like Ospreys, have to work hard for ground gained: their aviation fuel - stored fat reserves – gets used up more quickly. They suffer the same “sports injuries” as an elite Olympic athlete and face the same dilemma: stop to rest, heal and feed, or carry on and risk a bigger problem down the line.

My blog this weekend will look at the physiology of this in more detail.

THE LAST LAP

Different perspectives (1)

Here in this spring, stars float along the void,

Here in this ornamental winter,

Down pelts the naked weather:

This summer buries a spring bird.

“Here in this spring” Dylan Thomas 1933

It's a tough decision.

My nest is still almost five hundred kilometres away and, dammit, I need to get there. It's been a hard migration this year: my neck is sore, my chest hurts, my wing-bones are weary from hammering the sky. I would give anything for a rest - for a week, or a month, but it cannot be. The drive is too great: it screams at me in my head, like talons on wet glass...

I am in France, in Normandy. There is a nice river here, which I remember from previous years. There are fish in it, but I cannot eat too much. If I do, my body will go into post-migration metabolism, and long-distance journeys will be out of the question until the damage to my flight muscles has been repaired.

Maybe just a small one, then...

That's better. I got a good sight of the sun as it went down, so I know exactly where I am. Now, what to do tomorrow? There is a ridge of high ground here. I fly up and along it. Circling and climbing with the updraught, I reach eight hundred metres. Above me, the stars are beginning to come out. Not Dylan Thomas's stars – those are still far ahead, but from this altitude I can see the patterns of the sky beyond the sea.

(Click for larger image)

Instinct tells me to wait. Don't ask me how I know this: it's in the patterns in the sky. The wind is still against me, but it is less than it was today. That's a pattern too. Patterns are how we know things, how we navigate and tell the time, and find the places we belong. They are how the World works.

You humans see the patterns, but you no longer understand them. It is fortunate that you are not birds...

There were a few other ospreys here but they have gone ahead. I wonder if they made it. I will wait until the pattern in the sky changes. An extra day or two will not make that much difference.

After all, it's not as if anyone is expecting me...

OSPREY FACIAL EXPRESSIONS

and how to read them

Unlike us primates, birds do not have the underlying structure of facial muscles and other features which would enable them to communicate via facial expressions.  This makes it very difficult for humans to know what a bird's emotional state is at any given time.

Monty has been kind enough to employ his celebrated acting talents in this demonstration, which illustrates the problem...

(Click for larger image. Original (c) Dyfi Osprey project 2012)

So, how DO birds communicate with each other? There are two main methods: vocalization and posture.

Most of us are familiar with bird song in the Spring, and contact-calls can be heard some distance away.  But there are more subtle communication sounds made by birds, which we often don't hear because they operate at close range - when birds are at the nest, roosting, or feeding in flocks.

This season, and for the first time, Dyfi Osprey Project have equipped their nest platform with broadcast-quality microphones. Unlike other monitored nests, where the sound (if there is any) comes from microphones co-sited with the camera, these might reveal a whole new perspective on osprey communication.

I am totally stoked about this idea. It is going to be fascinating. -Wlw

Strange Attractor

Migration Forecast #3  

(Updated Fri 15.3.13)

 “The results are correct – just don't ask how it can be like that. No-one understands how it can be like that.” 

Richard P. Feynman: Quantum Electrodynamics 1990

Edward Lorenz thought he was going nuts.

For days, he had been running a program on his LQP-300 computer. The machine was large, noisy, inconvenient and (by today's standards) desperately slow – but in June 1962, it was the best that his department at the Massachusetts Institute of Technology could afford. Because of the speed problem, he would start the program, let it run overnight, and study the results next morning. And he was getting nowhere. Slowly.

Lorenz was investigating the behaviour of something called “hydrostatic convection flows in a non-Hamiltonian system” and, as a starting point, had written down some simple equations for this.

The difficulty was: every time this program ran, it produced a different result!

As a good scientist, Lorenz decided that – assuming he was not really going mad – there must be something peculiar about the way the numbers themselves worked out. And this was important, because Edward Lorenz wasn't actually studying mathematical oddities at all – he was trying to find out why the simulation models used in long-range weather forecasting kept being wrong. In time, his work (and that of others) led to a completely new discipline of science: Deterministic Non-linear Dynamics, more popularly referred to as “Chaos Theory”...

You've heard of this before. It includes features such as the “butterfly effect” - the proposition that an immeasurably small difference in the initial conditions of a system, can result in very large-scale changes in how that system behaves over time. Almost all climate and weather mechanisms are non-linear systems but – like the animals in Orwell's 1984 - some are more non-linear than others. The north Atlantic jetstream is one such and, around this time of year, it starts bustin' some seriously sharp dance moves:-

Click for larger image

All these loops and whorls in the jetstream are the signatures of chaotic behaviour. Most stable oscillating systems have a topological pattern to which they keep returning: an “attractor.” But the jetstream is NOT inherently stable. It marks the places where two different masses of moving air interact with other and the degree of turbulent interaction changes at every different position, repeatedly switching from one state to another. When scientists first identified this phenomenon, they had to invent a new term to describe this class of weird behaviour in Nature: “Strange Attractors.”

As of this week, we've seen unseasonably cold weather over much of western Europe: carnage on the roads in France, and hundreds of flights cancelled at German airports. And twelve kilometres above our heads, unseen, the jetstream writhes and dances, until suddenly...

Click for larger image

This is the chart of 850Mb isobars and wind direction forecast for next Thursday 21/3. The blocking anticyclone south of Iceland has vanished and winds will shift into the south-west, bringing much milder conditions over the British Isles. Will the strange attractor bring a tide of migrants home for the new nesting season? It should be so. 

Interesting stuff is about to happen... 

THE GATHERING STORM

Migration Forecast 2 (Part II)         (Updated Fri 8.3.13)

  

"The horrible texture of a fabric that should be woven of ships' cables and hawsers. A Polar wind blows through it, and birds of prey hover over it."    Hermann Melville, Letters (1851)

In Part I, we saw how seasonal changes in west Africa might be favourable for large numbers of migrants to undertake the first and most physically demanding part of their migration – crossing the Sahara. We also noted that there could be penalties for those individuals who come too far north, and too early.

Here comes that penalty now...

(Click for larger version)

… Low pressure area “A” - which is currently beating up the eastern seaboard of the USA - will consolidate and move out into the Atlantic. Deep depression “B” at 972mB (!) will also continue to track east and interact with low “C” off Greenland with fronts extending north-south, and will be off SW Ireland by midday Sunday, bringing high winds and rain with it.

The big problem is that we don't know exactly what will happen to these lows “A” and “B” during next week. There are two possibilities: they could continue on the normal path, bringing typically changeable early Spring weather to western Europe, which will soon clear. The second possibility is that a developing anticyclone “J” - which is currently off the chart, way up to the NE of Iceland – will extend south to cover most of the British Isles by mid-week.

This would bring a mass of very cold Arctic air down over the country which could, if mid-range forecasts are correct, show an influence as far south as Spain.

In this scenario, any migrants which have already made it over the desert and think that they are on the “home stretch”, might have an unpleasant surprise waiting for them in Europe. The next chart shows this forecast position but I stress that it is not very reliable yet.

(Click for larger version)

For small birds, this could stall them for several days until it changes. But ospreys are made of sterner stuff... I have gone over the weather maps for this time of year, all the way back to 2008. I compared the positions – especially wind speeds and direction – with the known arrival dates of ospreys at monitored nests. (Thanks Tiger and Chloe – your summary tables saved me a pile of time on this :)

Watching for brass monkeys
Pentland Hills, Scotland, 2004

What I found was that, although the weather conditions had some effect if it was REALLY bad, most ospreys managed to get through to their nest sites “on schedule”. True, there were exceptions to this, but remember that we don't know where most of these individuals spent the winter, so it would be unwise to draw too many intuitive conclusions.

Keep scanning the skies - even if it's snowing!

STOPWATCH RUNNING...

 … migration forecast #2

This migration overview is in two parts. Today, we concentrate on Africa where interesting developments are taking place as I write this:-

The Inter-Tropical Convergence Zone (ITCZ) boundary has finally shifted. Under its influence, circulation patterns in the region are beginning to change and – perhaps most importantly for our pre-migration birds – the Azores high-pressure area has been displaced by a major south-tracking Atlantic low.

Temp & Sea-level isobars for 12:00z 4/3/13 (Meteoradar.co.uk)

From tomorrow (Monday) we are predicting a step-change in daytime temperatures. For the past few months, things have been fairly cool (for west Africa) but this week will see midday shade temperatures > 36 DegC with peaks around 40 DegC in inland areas. Coastal winds, which have been fixed at north and north-easterly during the winter, will swing westerly and south-westerly, force 4-6, even > 7 over Morocco and the Straits.

These factors will aid north-bound migrants for several days, enabling them to get (literally) a flying start to the race.

A.Nesbitt/J.O'Brien
Subaru Impreza WRC
Irish Rally Champions 2002

On reflection, perhaps “race” is the wrong word. Spring migration is more like a car rally than a track race: The object is to arrive on schedule at each Time Control, and there are stringent penalties for a crew that clocks in too late – or too early.

For migrating birds, the analogy holds good: Get to your breeding grounds late, and the nest sites and territories might all be taken. Even worse, your mate from last season might have got fed up waiting and decided to start a family with someone else! But there could also be a penalty if you get there too early: the weather might be – probably would be – insupportably bad, and your summer food supply might not even have arrived yet. (This is certainly true for coastal ospreys. Don't forget that fish migrate, too...)

So it's all a matter of timing - with or without stopwatches. 

Next week, we'll look at weather patterns over Europe and see how these might influence our birds as they make their way north.

On Welney Bridge...

... a short story

The last time I saw her was on Welney Bridge. It was where we'd first met, four months ago while I was on secondment to the nearby Wildfowl Trust centre. Molly lived locally - I'd never have met her otherwise - and we sort of hit it off. (I'll spare you the background details – use your imagination. Yes, all of that too...)

WWT Welney lies in the very heart of the Fens, about two miles north-east of the village. It's not easy to get to, but the Fens'll do that – the roads of the area try to steer you away, make you decide to go somewhere else instead. This sounds a bit weird – and it is. There's one important thing to remember when looking at this vast horizonless landscape – it is wholly and completely man-made.

Hundreds of years ago, this whole area was fen indeed. Each autumn and winter, the sluggish rivers Nene, Bedford and Ouse would flood, backed up by the tides of the North Sea. It was a land of marsh, reed, and eel-traps, supporting a small rural population. Then in the 17th Century, a Dutch engineer was engaged for an impossible project – to drain the Anglian fens.

Cornelius Vermuyden knew that it was impossible, so instead he conceived a different idea – one that was four hundred years ahead of its time: a washland flood control system. Working only with picks, shovels, and wicker baskets, teams of labourers dug two immense cuts to intercept the eastern fenland rivers. For more than twenty miles these canals slash across the landscape, straight as a pair of parallel rulers. And between them lie the fields which are still allowed to flood in due season, taking the excess water from the channels: the Ouse Washes.

In summer they provide rich grazing for livestock, and in winter a refuge for wildfowl from all over northern Europe, most importantly the wild white swans.

“You came then. I wasn't sure if you would.”

Her voice was quiet and steady. No blushing English rose this, but a daughter of some Jutland tribal diaspora. Molly was slim as a fen-willow, fair and pale and blonde with sky-grey eyes. Like my wife's eyes, but younger, of course – because if you're going to be a complete swine, you might as well go the whole hog.

“I said I'd be here. Didn't you believe me?”

I couldn't look her in the eye directly, for reasons already given. Instead, I leant against the brickwork pier of the bridge and looked upstream. It was early spring and early morning, cold and misty. But something had told the birds that this was already time to leave. In parties of increasing size, they took off from the water and followed the river towards the bridge, wheeling away into the north. Soon, I would be going in that direction myself. 

 

There are two species: whooper swans Cygnus cygnus are the noisy ones; their trumpeting contact calls ring out for miles across the Hundred Foot Drain and the New Bedford River. They're shy of people – except for the juvenile females, birds of the year. Knowing no better, they tend to trust everyone.

Smaller and more graceful, the Bewick's swans Cygnus columbianus had already departed for their Siberian breeding ground. It's a long journey and perilous, but it's where they call home.

 “Are you going to stay?” The steadiness had faltered a little.

“Of course I'll stay with you. I love you, don't I? We'll always be together.”

Now, the rhythmic thump of the birds' wings was directly over our heads, and their twin-tone voices split the morning air:-

“LIAR! .. -LIAR! .. -LIAR!”

She didn't speak, but simply turned away. The last I saw was her grey form merging into the mist, along the road below Welney Bridge.

Women always know when you lie to them.

After all, think how much practice they must get.