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Home > Blogs > Birds and Butterflies > Archives > 2009 > September > 23 > Entry
The Science of Migration
Tree Swallow at Sugarcreek MetroPark by Katy Malcolm
Guest Blog By: Katy Malcolm
As many are already aware, this is an exciting time for the avid birdwatcher. Everywhere we look, birds are coming together, preparing for the trip south. Tree swallows are lining the power lines along the country roads, chattering and feeding.
Aristotle believed that swallows hibernated. Research has shown us that this is not the case. Migration is an amazing physical feat and I broke out my old ornithology book to learn a little more.
Migration behavior occurs is by a decrease in day length. When the days reach a certain length, it triggers the body to stop releasing the hormones that stimulate parental care and breeding behaviors. This allows for other hormones to be released that stimulate increased feeding and the building up of fat stores. Birds that migrate in groups may start to exhibit flocking behaviors. These hormonal changes are essential to the migratory pattern since males would be so busy competing and working to attract females, they would not be eating to prepare for the flight.
In terms of navigation, many different strategies are used. Our friend, the tree swallow, migrates during the day, catching insects on the wing. The sun, landmarks, and potentially metal deposits in the brain help it find the way. Birds migrating at night also use their internal compass but may rely on the stars as well.
Migration length is different depending on the species of bird as well as individual populations. Tree swallows overwinter along the Gulf coast while some of our local warblers can be found as far south as Ecuador. Upon arrival to the winter grounds, birds are exhausted and their fat stores used up. Some fly over large bodies of water all day without a break. This type of travel produces a lot of wear and tear on the birds and many are not successful.
Many theories exist as to why migration is beneficial. Why would the birds want to leave a tropical paradise in the first place? It is thought that food sources are not adequate to support so many breeding birds. Space is also limited and may have a negative impact on the breeding success of the birds. Another thought is the difficulty of finding food during a long harsh winter; migratory species are generally insect eaters. So, even though migration is tough, it appears to be worth it!
We have two workshops coming up on Sept 26th! Our Begining Birding Workshop runs from 8am-12pm and Our Birdsong Study is from 1-4pm. Both classes are taking place at the Germantown Nature Center classroom. For more info call 937-277-4178.
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