Scientists say that Barnacle Geese do no ‘training’ for their epic 2,500km migrations, needing just 22 minutes flying a day to keep their flight muscles in good condition.
“The same is likely to be true for all migratory birds,” said Dr Steven Portugal from the Royal Veterinary College, lead author of a study published in Biology Letters.
Scientists have long known that migratory birds’ flight muscles tend to bulk up considerably before they set off, and it had been suggested that they would have to exercise to prepare for a long-distance flight.
But now new evidence from captive birds shows that their muscles waste away or bulk up without any change in muscle use or increase in exercise levels.
Dr Portugal and colleagues from the UK, Australia and Canada tracked six Barnacle Geese throughout the year, recording their heart rates to find out how much time they spend in the air.
“It’s easy to see from their heart rate when they’re flying’, explained Portugal. “When they’re on the ground looking for food, their heart rate averages about 80 beats per minute, but this rises to 400 beats per minute when they fly. Flying is really hard work, so they limit it.”
Dr Portugal and his colleagues found that the geese didn't spend any more time in the air immediately before a migration than at any other time of the year.
“To not see any increase is quite surprising. They complete a 2500km journey in under a week. That’s a lot of time flying. They should in theory be flying around a bit more, but it looks like the birds’ muscles just get bigger, right on cue for migration.”
The extra weight that birds put on before they migrate might actually be enough to exercise their flight muscles.
Other researchers have found that key components of many birds’ metabolic pathways rise just before they migrate.
“But these components don’t seem to be stimulated by an increase in exercise,” Portugal explained. “The changes in the flight muscles we see could be to do with hormones or light levels. The next area for research will be to look at the birds’ hormones to see if they’re controlling what’s going on.”
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Barnacle Geese need only 22 minutes flying time a day to keep in their flight muscles in good condition
