Above: Found throughout Canada, many Canada geese migrate to the southern United States and even northern Mexico for the winter (Wikimedia Commons/Ken Billington)
Did you know? The bar-headed goose migrates through the Himalayas, regularly reaching an altitude of 7000 m above sea level. Some people have reported seeing the bird fly over Mount Everest!If you left on a cross-country road trip, you might use a GPS receiver, a compass, or a road map to guide you. Birds have none of those luxuries, yet they manage to return to the same breeding and wintering grounds year after year. There are several theories as to how birds get from one place to another. Research has shown that the bird orientation toolkit includes several interactive senses. For example, birds use landmarks, the position of the sun, the stars, and the topology of the Earth’s magnetic field.
Over 75% of bird species native to Canada spend about half the year outside the country’s borders. In fact, every year around 5 billion birds leave their breeding grounds in Canada and parts of the United States for warmer climes in Central and South America. Many migratory routes involve travelling more than 10,000 km! For example, the Bar-tailed Godwit flies from Alaska to New Zealand and eastern Australia. a mind-boggling 11,000-km nonstop flight.
Did you know? In order to have enough energy to fly such long distances, migratory birds bulk up on food before going on their long journey. Some species, like the blackpoll warbler, double their body weight in preparation for migration. Not only do migrating birds cover vast distances, they can even manage to reach their destination after a major detour. In the 1960s, researcher Richard Mewaldt captured white-crowned sparrows in their wintering habitat near San Jose, California. He then flew them to either Baton Rouge, Louisiana, or Laurel, Maryland, before releasing them. Even after being transported between 2,900 and 3,900 km from their wintering grounds, about a quarter of the birds were captured the following year back in San Jose!
Many birds migrate at night, and researcher Stephen Emlen from Cornell University has used a closed planetarium to show how birds use the stars as a compass. He raised birds in varying conditions, from a windowless room to an irregular and normal night sky. Some birds were then exposed to a night sky that rotated normally around the North Star, while others were put in the planetarium under a manipulated night sky that rotated around the star Betelgeuse. Birds that were exposed to the offset star pattern were unable to orient themselves in the correct migratory direction. The results of the experiment showed that young birds learn a north-south orientation from the night sky and use it to migrate between their wintering and breeding grounds.
Other birds use a magnetic compass to navigate. German scientists studying the European robin placed individual birds in covered cages during migration season. Without any visual cues, the robins still managed to hop along their normal migratory direction. Next, the researchers placed a Helmholtz coil—a device capable of shifting the direction of the Earth’s magnetic field—around the cages. Immediately after the the direction of the magnetic field was altered, the robins changed their migratory path and hopped along in a different direction.
Did you know? Not all migratory birds fly to their destination. Emperor penguins, for example, march 100-160 km to their breeding grounds in Antarctica.Ultimately, these experiments only provide a tiny glimpse into how birds orient themselves during migration, and scientists are constantly looking into new possibilities. There is also evidence that some bird species use multiple compass senses, relying on different ones as conditions change. After all, how would a bird relying on the night sky navigate when it’s cloudy? Ongoing research should provide even more answers to how that same bird shows up at your backyard feeder year after year!
The State of Canada’s Birds (2012)
Environment Canada/ North American Bird Conservation Initiative Canada
Detailed report on birds in Canada, based on 40 years of data. Includes a section (Beyond Our Borders) on migratory species.