The Atlantic shearwater is one of the most wandering migratory birds in the world: every year it travels up to 20,000 km to chase the heat. And their extraordinary traveling skills are not limited to seasonal changes: when they have to go in search of food they travel hundreds or even thousands of kilometres.
To orient themselves during these journeys they use a combination of the position of the sun and their internal clock: the problem is that, when they travel long distances, the two parameters can go out of sync, similar to what happens to us humans when we suffer from jet lag. The discovery is reported in a study published on Science.
Jet lag in birds
The study arises from purely theoretical reasoning. Atlantic shearwaters, like many other seabirds, breed along the west coast of the UK and Ireland and when they need to forage for food, they fly westwards. To know which direction they should follow, they use two sets of information: the position of the sun and their internal clock, which is reset every morning at dawn and helps them take into account the fact that our star moves during the day.
The problem is that, when they have to return home, they fly east, crossing areas where the sun rose earlier: their internal clock thus risks “falling behind” by up to an hour.
To test this theory in the field, the Oxford University team had an enormous amount of data available: twenty years of GPS tracking of more than 1,000 shearwaters, for a total of 3,688 trips west and back. What they found was that these birds actually deviate from their intended path, and do so in a manner consistent with differences in the position of the sun.
In practice, this means that when they travel east to return to their nest, they tend to deviate clockwise from the correct direction – exactly the error you would expect from birds that rely on the position of the sun to navigate.
The sun as the only compass
Analysis of the shearwaters’ navigation data revealed other interesting details. First of all, disproving another of the hypotheses about their navigation errors, namely that they may be based on changes in the Earth’s magnetic field: the numbers do not support it.
Another detail is the fact that the involuntary deviations of these birds also occur when they fly close to the coast, that is, in areas where they could use other points of reference in addition to the sun, demonstrating the fact that our star is their only compass.
It is worth pointing out, however, that we are not talking about total disasters: the deviations recorded never exceeded 15°, and the average was around 7°; in practice this means that, over a 1,000 km journey, shearwaters add just 5 km due to jet lag. And on the other hand, these birds continually correct their flight path, compensating for errors.
However, this does not apply to all “travellers”: for example, birds on their first migration may not yet have the tools to correct their trajectory, and errors could accumulate, leading to deviations of tens or hundreds of kilometers. Then there is the question of the physiological effects of jet lag: is it possible that birds suffer from it like we humans do? To find out, new studies will be needed.
