Restless Heart

Zugunruhe - migratory restlessnessTo regular readers of this blog, my love of obscure words is not a new thing. Over the last few years, I’ve been creating these ‘definition images’ as my way of bringing life to some of the wonders of nature and the words used to describe them.

Looking back over them all, I realized, much to my surprise, that I’ve crafted more than 70 of them, covering just about every letter of the alphabet. That discovery has led me to challenge myself to visualize words starting with more uncommon letters, like  X, Qand Z. Kind of like an artistic variation on Scrabble.

Autumn has given me the perfect opportunity to address one of my favourite Z words.  It’s another one of those terms that comes up only in the discussion of natural history and animal behaviour and it never fails to raise a few eyebrows if you manage to slip it into regular conversation.

The word is Zugunruhe.

Zugunruhe is a combination of two German words = Zug, meaning to move or migrate and Unruhe, meaning restlessness and it together, the sum is really the combination of the parts: migratory restlessness. For a behavioural ecologist, it’s a word that tends to conjure up thoughts of autumn, or more specifically, late summer.

As the earth lumbers along its orbital path and those of us in the Northern Hemisphere find ourselves canting away from the sun’s warmth, many creatures get antsy. Birds especially are seized by a sudden disquiet and activity levels skyrocket. Sleep patterns change and if the individuals are kept in a cage, they start orienting their activity in the direction they should be migrating in. Most species go through a period of excessive feeding, needing to pack away as much energy as aerodynamics will allow for the journey that inevitably lay ahead. We see it all around us in the clouds of blackbirds roiling through the air or flocks of geese descending on a recently-harvested field. This period of restlessness is referred to as Zugunruhe by biologists who study animal behaviour and it’s a phenomenon observed both in the spring and in the fall, just prior to the mass migrations that move millions of birds along north-south flyways over the continent.

Here, in the boreal forest, it’s a phenomenon that usually starts in August. Our summers are relatively short and as soon as breeding is over, the preparation of the twice-yearly journey gets underway, especially in songbirds, who have to travel thousands of kilometres to Central and South America. With their time here so fleeting and the journey so long and fraught with danger, you can’t help but wonder, why go through all the trouble?

Why not stay in the tropics, where the weather is favourable and save all of the energy and risk associated with long-distance travel? The answer to that question likely varies to a certain degree between species; but evidence suggests that food, or rather the lack of it, was likely the driver behind the evolution of long-distance migration in many birds.

Most of today’s migratory species likely evolved near the equator, enjoying consistently tolerable weather and relatively abundant food. However, as populations started to grow and segment into different species, the pressure on food sources grew to a point where the survival of some depended on searching out new resources. The only place to go was away, into the temperate zones north and south of the tropics. Those that did, discovered abundant resources, millions of insects, and a glut of fruit and vegetation. The problem was it only lasts for a short period of time, forcing those explorers to retreat back to the warm haven to the south during the winter months.

Over millenia, these paths have been extended and entrenched by generations of birds winging their way along now well-established routes.  As those paths have become increasingly ensconced in the collective memories of each species, so has the irrepressible need to travel those routes that spurs everything from hummingbirds to harriers on their way twice a year.

With migration in full swing here in Manitoba, the period of zugunruhe is actually over; but once balance of night and day swings back into the favour of the light, the millions of birds enjoying the warmth of their winter homes will feel the inexorable pull once again, the restlessness building until one day, they’ll have no choice but to take to the air and find their way back to us.

And I see your True Colours Shining Through

My favourite season tends to depend on my mood, but most often, my answer is autumn. It’s refreshing, a cool breeze washing away the heavy haze of summer. Paradoxically, it also feels warm, like shrugging into your favourite coat as you catch a whiff of someone’s wood stove in the crisp morning air.

I think it’s the colours of fall that give the days their warmth. The cool greens slowly fade into yellows, golds, russets and umbers. The forests are suddenly ablaze with a riot of hues.

In the boreal mixedwood forest where I live, the dominant colour is yellow. The poplars and birches sparkle with it against the sapphire September sky. Still, if you look closer to the ground, you can find a little more variety. The dogwoods (Corylus stolonifera) go purple, their leaves a lovely compliment to their reddish branches. The mountain maple (Acer spicatum), like the one pictured above, show quite a bit of variation, ranging from a pale yellow in individuals that are growing in the shade to brilliant orange and deep red for those lucky shrubs that are exposed to full sun.

But, where do these colours come from?

To a certain degree, they’re always there, hiding just below the surface, waiting for their curtain call. New, functioning leaves are full of chlorophyll, a brilliant green pigment that is packed into structures within the cell appropriately known as chloroplasts.  These are the food factories for the tree, working throughout the growing season to transform carbon dioxide and sunlight into nourishing sugars via photosynthesis that are then funnelled into the rest of the tree. During this period, chlorophyll is constantly being degraded and replaced, keeping the leaves a brilliant green, overshadowing any other colours lurking within.

However, as the days become shorter and the sun’s intensity begins to wane, these factories shut down, using up their last stores of chlorophyll until there’s nothing left. Once the green is gone, the veil is pulled back giving other the hues a chance to shine. Carotenoids, a pigment that also plays a role in photosynthesis, remains, painting the trees with bright yellows and oranges. Some leaves also contain pigments known as anthocyanins, a watery dye that stains leaves with intense washes of reds and purples.

Just how bright and varied the fall palette is depends a lot of the weather. Warm, sunny days, followed by cool, but not frosty nights gives the leaves a chance to build up a lot of sugars and trap them within their cells. High sugar levels often results in greater amounts of anthocyanin, yielding more reds and purples, adding to the variety in the forest.

This year’s fall in the north woods has been just the kind we need for a spectacular display and the trees have not disappointed. Every day for the last few weeks, I’ve watched in awe as more and more of the canopy sparkles with colour, filling in the autumn landscape, a spectacular display against the clear blue skies.

Still, all good things must come to an end. Eventually, the nights get too cold and the days too short, signalling to the tree that it’s time to lock down for winter. The veins bringing moisture to the leaves close up and the branches seal over, cutting off the leaf’s lifelife. The late October winds howling off the lake will tear the foliage from their bases, sending them fluttering to the forest floor and returning their nutrients back into the soil to feed next year’s crop. However, those days are a little ways away, and in the meantime I plan enjoy nature’s yearly blaze of glory for as long as I can.