As the leaves turn and the evening chill sets in, a new season is upon us. Usually by mid October, the fall migration of birds through the Creston Valley is in full swing.
Approximately 1,800 of the world’s 10,000 bird species are long distance migrants, traveling hundreds to thousands of kilometers each year to northern breeding grounds in the spring and summer and southern overwintering areas.
The primary motivation of migration is to obtain access to abundant food supplies. The longer days of the northern summer provide greater opportunities for breeding birds to feed their young. As the days shorten in autumn, the birds return to warmer regions where the available food supply varies little with the season.
Migration is triggered by many different factors. Birds don’t read calendars, but they are very in tune to the seasonal changes in weather, daylight and food supplies. They move on mass to take advantage of areas with a rich food supply.
Birds that migrate through Creston area are following a route called the Pacific Flyway. Different flyways exist around the world and these routes typically follow mountain ranges or coastlines and may take advantage of updrafts and other wind patterns or avoid geographical barriers such as large stretches of open water. The specific routes that the birds fly may be genetically programmed or learned to varying degrees.
Many northern breeding ducks, geese and swans are long-distance migrants, but need only to move from their Arctic breeding grounds far enough south to escape frozen waters. Here in Creston, some birds stay year round, but most will migrate further south to where water remains open year round and the food supply is more abundant. Great blue herons can be seen year round hunting for fish in open water holes in the frozen ponds that are created by river otters.
Many of the larger birds, such as geese, pelicans and swans fly in flocks when they migrate. Flying in flocks helps reduce the amount of energy needed by reducing wind resistance. Many large birds fly in a V-formation, which helps individuals save 12–20 % of the energy they would need to fly alone.
For many species, migration success depends on the availability of certain key food resources at stopover points along the migration route. This gives the migrants an opportunity to "refuel" for the next leg of the voyage. The wetland in Creston provides the ideal stopover, giving birds a chance to feed and rest before continuing on their long journey.
Birds navigate their migration route by using a variety of senses. Many birds have been shown to use the sun and stars as a compass, making compensation based on the time. Navigation is also based on a combination of other abilities including the ability to detect magnetic fields, use visual landmarks as well as olfactory (scent) cues.
Migration demands a lot of energy. Birds store energy in the accumulation of fat. If you look at the size of some of the hummingbirds in the weeks before they migrate, they look like golf balls with wings because they are storing fat for energy for their long journey south. Migration puts a lot of wear and tear on a birds feathers as well. Many birds molt, which means they shed their old flight feathers and grow back new ones. During the summer here, many duck species shed their flight feathers and become flightless. That is why you tend to not see too many ducks flying around in the summer as they stay hidden until their flight feathers grow back.
So, keep your eyes and ears open for migrating bird species this fall. Different species are arriving daily at the international airport known as the Creston Valley Wildlife Management Area. What a great location for a stopover!
