Migratory birds are extraordinary endurance athletes – and their feats require some serious preparation. In the weeks before take-off, many undergo extreme physiological changes (Vernimmen, 2017). Most obviously, they load up on fats. In many cases, that means temporarily supersizing their digestive organs to ingest as much food as possible. Then, immediately before departure, they shrink their digestive organs to reduce their flying weight.

But that is not all. At least one species indulges in what Jean-Michel Weber at the University of Ottawa, Canada, describes as “natural doping”. Weber noticed that the semipalmated sandpiper, which flies non-stop from the Bay of Fundy on the east coast of Canada to South America at the end of every summer, mainlines on mud shrimp before departing. Mud shrimp are loaded with omega-3 fatty acids, and Weber suspected that these compounds boosted the efficiency of the sandpipers’ muscles. To isolate their effects from other factors, he turned to a more sedentary bird. Sure enough, when he fed bobwhite quails a cocktail of fatty acids equivalent to the diet of the sandpipers, the amount of oxygen that their muscles could use shot up by 58%.

Migrants’ preparations do not stop there. Several species, including the red knot, are known to bulk up their heart muscles so they can pump more oxygen-rich blood around the body. The bar-tailed godwit, however, might have the most effective way to supercharge aerobic capacity. Its levels of haemoglobin, the molecule that carries oxygen around the blood, increase considerably in the weeks
before migration.

That helps explain how the godwit can fly for more than 11,000 kilometres without a rest. This epic journey, revealed back in 2007 by one of the first big satellite-tracking studies, makes it the longest known non-stop journey by any bird. Another factor is that the godwit does not rely on fat alone. “Many birds will also break down muscle tissue along the way,” says Hedenström. “Muscle proteins contain plenty of water, which helps to avoid dehydration.”

Reference

Vernimmen, T. (2017) How Do Birds Get in Shape? New Scientist. 25 March 2017.