In a short article written for Northern Woodlands as part of their “The Outside Story” collection, Rebecca Perkins Hanissian ponders her relationship to migratory birds. Specifically, she notices the evolutionary traits she may have in common with birds. Besides this being a humorous read about human behavior, this article identified a five avian adaptations worth sharing.
Zugunruhe is a German word that means “migratory restlessness”. In birds, this refers to the increased activity that happens during the spring and the fall. Scientists believe that this “restlessness” is brought on by internal and environmental cues such as the length of day and hormonal changes.
Hyperphagia is basically overeating. Birds typically engage in hyperphagia prior to their migration periods. Overeating allows them to store up energy for their long migratory flights. The graph below from American Scientist shows the relationship between hyperphagia, or fattening, and migration.(3)
The graph above also shows the molting period for migrating birds.
Bird feathers are made up of the same substance as human hair and nails: keratin. This is important because it means that feathers, much like hair and nails, cannot repair itself. Instead, worn or damaged feathers need to be replaced. The process of replacing feathers is called molting.
In order to keep the flight feathers in top form, birds often molt prior to migration. Molting takes a fair amount of energy so it usually occurs prior to the fattening period. You will notice in the graph that molting and fattening are overlapping in the spring but separated out in the fall. My suspicion is the difference is a result of the availability of food in the summer and the influence of the breeding season.
It should be noted that not all birds molt at the same time or at the same rate. Some birds such as chickadees only molt once a year, where as marsh wrens molt twice.(4)
Thermoregulation is the scientific word for behavioral and physiological traits that are used to help regulate body temperature. Birds who spend the winter in colder climates can grow up to 25% more feathers to help them insulate their bodies.(1) However the unfeather parts of their bodies, such as their feet and legs, can’t benefit from these extra feathers. Instead they are able to constrict their blood vessels and limit the blood flow into the feet which will reduce heat loss. This process is called vasoconstriction.
Not all migrations are equal
Not all birds migrate. But those that do migrate, don’t all travel the same distance. Bird migration can be separated into short-distance, medium-distance, and long-distance.(5)
Short-distance migration may look like a bird traveling from the mountainside to the lower plains, or from one hunting ground to another.
Medium-distance migration usually falls within a couple of hundred miles.
Long-distance migration can be several hundreds of miles. For example, the broad-winged hawk migrates about 4,300 miles from New England to South America.
Hannissian did a wonderful job highlighting the fact that humans might share some of the same behaviors as birds. She mentioned that she eats more in the fall and winter (hyperphagia), she often dreams of going south and becomes restless when trapped inside (zugunruhe), and practices thermoregulation by putting on her down coat. Her essay really makes me wonder, that despite our best attempts, we really aren’t that different from the other-than-human species that share this planet.
You can read Hanissian’s full article here.
“The Outside Story” is a series of ecological articles written for Northern Woodlands and subsequently found in newspapers of Vermont and New Hampshire since 2002. Learn more by going to NorthernWoodlands.org
- Rebecca Perkins Hanissian: “To Go or Not to Go? How Birds Weather Winter”, Northern Woodlands
- Dr. Maria Wheeler-Dubas: #bioPGH: Zugunruhe!, Phipps Conservatory and Botanical Gardens
- Americanscientist.org: Avian Migration
- AllAboutBirds: The Basics, Feather Molt.
- AllAboutBirds: The Basics Of Bird Migration
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