Migration doesn’t happen for #everybird; some parts of the world provide enough stable conditions for birds to remain in that same place all year for each year of their lives: these birds are known as resident birds.
It is possible that they will move to somewhere else for a mile or two, such as into woods in the summer to hide from the heat after spending the winters in open grassland or near water.
What’s more, they often don’t even fly.
But for the rest, they are off up and into the air, obeying some innate and instinctive order, likely triggered by changes in daylight hours, food availability, and temperature.
In and of itself, the feat of migration is spectacular – just taking off and leaving the place you’ve called home for the past 5 or 6 months to spend days, weeks even, flying constantly save for a few short-lived breaks to refuel on food and rest, eventually ending up many hundreds or thousands of miles from where you started.
But today we want to look at a couple of birds who make our jaws drop and wonder at the world we are yet to discover.
Grousing around
First, though, we think this guy deserves a special mention for essentially that kind of easy-going bird we all aspire to be. Twice a year, one species of bird makes the shortest known journey of “true migrants”: the North American Blue or Dusky Grouse.
This plump, steely-grey blue bird inhabits the pine, aspen and fir forests of inland western USA and Canada and is the third largest grouse around, coming in at just over 1kg with a height of around 50cm / 20 inches. They are ground nesters, which means that when those snowy harsh winters hit, there is little point trying to breed if your eggs are going to freeze right away.
Whilst they don’t exactly move very far, it’s far enough for them. They simply descend around 300m to warmer woodlands where they will find more food and take advantage of the early crop of seeds and fresh leaves in the spring.
Some have been known to travel 10miles, but that is rare. What’s more, they often don’t even fly, just stroll downhill with the occasional half-hearted flapping.
No mountain high enough?
The Bar Headed Goose, our cover star, stands out for its method of migration, as not only does it go far, it goes high…
They can fly through air that contains less than 10% of oxygen.
These sturdy geese spend their winters in India and then fly over the Tibetan Plateau and China to eventually spend their summers in Mongolia, breeding yet more remarkable aviators. On their journey, they fly UP the mountains rather than around them, probably because that would be a huge detour.
They can fly through air that contains less than 10% of oxygen than at sea level at altitudes of around 7000m, although some mountaineers have reported seeing them fly over the summit of Mount Everest.
They have been tracked over the years and can be seen to “hug” the mountainous terrain as they go over it, perhaps using any air uplift from wind trapped beneath cornices and over cols, and they also tend to fly at night: even though conditions make it harder to do so, they avoid predation far easier this way.
But this resistance to conditions continues to baffle scientists to this day. They rarely glide, and will have long periods of intense flapping during those absurd climbs. This effort requires a much faster heart rate and metabolism, which require greater amounts of oxygen to operate, so how do they do it? Evolution.
Although yet to be thoroughly explored, scientists have concluded that they have evolved a superior way of transporting oxygen during times of extreme O2 deprivation, making sure there is enough to go round.
To the moon and back. Once or twice.
The Arctic Tern does not do things by halves. Every year this blade-shaped bird has a circumpolar breeding distribution, which means it just keeps going up and down the globe throughout its breeding and wintering cycle. In fact, it flies so far it can be said not to fully experience a winter at all.
This medium-sized bird manages to squeeze in two summers a year.
To the envy of many a holiday-maker, this medium-sized bird manages to squeeze in two summers a year and sees more daylight than any other animal on the planet on this Herculean journey. It leaves its breeding grounds in Greenland at the end of the northern summer season and heads south, following the coastlines of Europe and Africa, turning east at the tip of Cape Agulhas and making it halfway to Australia when it turns south again for the Antarctic, in time for the southern summer.
They can live to be around thirty years old, meaning some of these birds will travel approximately 2.4 million km (1.5 million miles) during their lifetime; that’s the equivalent of a roundtrip from Earth to the Moon over 3 times.
Migration has long been a mystery for us humans who just love to know what is going on all the time. So many studies have been carried out over the decades, even centuries, but we still don’t really understand the mechanisms at work.
Excellent theories abound that are in all likelihood true, but until either we or the birds come up with a common language, they are not giving up their secrets anytime soon.
