Richard Collins: Bird migration is dangerous and demanding — why do it?
And Half Their 120 Fitted Heart Winter Every Throughout Tempearture Picture: Data To Birds Devices Scientists Logging Hour Body Measure Istock Rate To
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Some of us are stay-at-home birds, while others are restless souls not content to remain in one place for long. There’s a motor vehicle for every two people in Ireland and more than a million passengers are airborne, worldwide, at any given time. How odd!
We evolved as hunter-gatherers, roaming a small ‘home range’ on two legs throughout our lives. Why, then, are we such slaves to the wanderlust?
Nor is the lure of far-off hills confined to humans. Wolves grey whales and reindeers travel vast distances. European swallows spend the winter in sub-Saharan Africa, while brent geese from Arctic Canada visit our estuaries.
Some blackbirds, caught for ringing here in winter, are unusually heavy. These tend to be visitors from Scandinavia. We also get English and Scottish ones. Meanwhile, many of our native blackbirds head south.
As well as the frequent flyers, there are ‘sedentary’ and ‘partial migrant’ species. Like people, most Irish songbirds are of the some-do-some-don’t persuasion when it comes to travel. They have a foot in each camp.
Far off hills may be greener but migration is demanding and dangerous. So why do it?
New study on blackbird migration by @nilslinek @scottyanco is out today and covered by @NYTScience 🐦⬛🐦⬛🐦⬛
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Ornithologists thought that the reason was obvious; it was down to energy saving. The overall energy needs of a bird moving to a warmer environment for the winter would be lower than if it were to remain at home.
Now, however, in a paper just published, scientists from the Max Planck Institute and Yale University question this assumption. They compared the energetic costs of migrating blackbirds with those of their more sedentary peers.
Like our Irish ‘lon dubh’, the ‘amsels’ of southern Germany are partial migrants. The researchers fitted data-logging devices to 120 of them. The units recorded heart-rate and body-temperature every half hour from autumn to spring, throughout the winter.
The researchers expected that moving to a warmer environment would lead to an energy saving, otherwise why would a bird undertake such a hazardous journey? However, on analysing the huge quantity of data obtained from the monitors, the scientists concluded that the standard textbook explanation is wrong.
"We never expected to discover that birds gain no overall advantage by escaping cold winters" lead author Nils Linek is quoted as saying on the Max Planck website. When blackbirds are in a warmer climate, "they don’t appear to reduce total daily energy expenditure".
But the experiment led to the discovery of a previously unknown mechanism. The data from the sensors showed that blackbirds begin to reduce their metabolism three weeks before setting out on migration. "They are essentially turning down their internal thermostat, allowing them to save energy for the journey ahead," says Linek.
But where does the surplus energy they save go?
The researchers admit that they can only speculate about this: "We suggest that there may be other physiological adaptations or hidden costs that migrant blackbirds face in their milder overwintering sites." These might include a need for increased vigilance, ‘immune functions’, or ‘unknown stressors’.