Mention the word “migration” to just about anybody, and it will conjure up images of mass amounts of birds flying through the air to some far-off destination for several months. That much, assuredly, is true – nearly 1800 of the 10,000 species of birds around the globe are classified as long-distance migrants, embarking on a seasonal journey in search of better weather and subsequently more food. What may not cross many people’s mind, however, is exactly how birds prepare to attempt such a daunting undertaking. After all, if the birds are migrating in search of more food, then where do they get food during the migration itself?
As it turns out, birds long ago solved this problem by opting instead to absolutely gorge themselves before ever setting off on their voyage. It’s been discovered that birds can eat as much as three times their body weight in berries prior to their trip – berries being the pre-migration food of choice for many birds, even those that prefer insects during the rest of the year. Why is this, however? What would cause a bird to completely, albeit temporarily, change its diet – and not only that, but to eat so much of its new preferred food?
As can be expected, migration is a highly stressful time for all birds involved. One of the best remedies for high levels of stress is antioxidants. Conveniently, berries are loaded with antioxidants – which is primarily why birds make the seemingly clumsy switch from insects to fruit before migrating. Although the birds may add on extra fat as a byproduct of eating nearly three times their body weight in berries, this – contrary to what is probably conventional wisdom – is not the primary motivating factor. The berries are eaten merely to help reduce stress. Add this to a concurrent increase in the consumption of lipids – which contain over double the amount of calories per gram than either sugars or proteins – and birds are all set for their migration, having loaded up on stress-resistant and high-energy foods beforehand.
So now the next time you see a sparrow, thrush or other clearly insect-eating bird fumbling around with some kind of berry in the fall months, you’ll have a better idea of why this curious scene happens.
– By Sean Peick (Guest Writer)
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