The sound of hawks spreads through the sky as they travel in their V-shaped formation. For nature observers, this beautiful movement represents bird migration. In North America, there are more than 650 bird species. Though some are permanent residents, the majority of species are migratory. Bird migration has many underlying reasons such as climate, food scarcity, breeding, and genetic disposition. Our own nomadic ancestors, who were hunters and gatherers, migrated for thousands of years to escape drought and food scarcity, so the idea of large-scale migration is not so uncommon.
Insight on the how and why of bird migration helps us figure out why migration is a vital trait. Scientists today continue to study bird migration and its origins to uncover the mysteries of how evolution has crafted birds into astute navigational creatures, and how to protect ecosystems important to bird survival.
Understanding bird migration is also another way to combat stubborn creationists, who claim that evolution is not real. Recently, scientists discovered fossils from Mesozoic-aged rocks that point to a direct link between a group of dinosaurs, known as maniraptoran theropods, and the birds of today. With no hesitance, they announced that birds evolved from dinosaurs.Migration is a movement of birds between their breeding or summer homes and their non-breeding or winter grounds. Birds tend to migrate from one area to another in search of resource—moving from a place of scarcity to one with an abundance of food and nesting locations. Birds of the northern hemisphere migrate northward in the spring to benefit from the insect population, plant life, and nesting locations. Once winter begins and there’s a reduction of insects and other food sources, the birds move south again.
Not all birds travel the same distance. Short-distance migrants cover ranges such as high to low elevations, medium-distance migrants covers a range of several states, and long-distance migrants cover ranges that can extend from the US. to Mexico, and even farther south.
Bird species tend to follow numerous routes called flyway systems. In North America there are four major flyways: Atlantic Flyway, Mississippi Flyway, Central Flyway, and Pacific Flyway. Though migration is at its peak during spring and fall, there are birds migrating throughout the year. Several weeks or days before migration, birds enter hyperphagia, a state where hormone levels force them to increase their body weight to store fat for later use as energy while they travel.The origins of long-distant migration involve complex scientific studies and experiments, not always resulting in a full revelation of the inner-workings of migrations. So far, scientists know that temperature, variations in food supplies, and genetic predisposition affect migratory patterns. Birds can also face unpredictable forces, such as storms, physical weakness, or predators during their journey, causing a change in flying patterns. For example, some birds migrate during the night, since the cooler weather makes it easier. Songbirds migrate at night, to avoid feisty predators lurking during the day, while hawks, swifts, swallows, and waterfowl find it more suitable to migrate during the day. Usually birds will fly down to unexpected locations where they can rest and feed before arriving at their destination. This type of behavior causes migrant traps, usually advantageous for bird-watchers. Migratory patterns have evolved over thousands of years, making the necessity to migrate integral to a bird’s genetic makeup. Scientists attribute the learning process to the first bird communities which flew in different directions, and later learned what direction was more beneficial. The memory of later birds kept pointing to a southern direction during winter. Birds inherited the knowledge of directional flying in order to find warmer weather and food, so it’s possible that their genetic memory is triggered by external conditions. Scientists present the evidence that young birds already know to fly toward the north in the spring without help from adult birds. Birds cover thousands of miles in their annual travels, making the same course year after year. At their disposal is a set of navigational skills, including navigation by the stars, sensing changes in the earth’s magnetic field, and even smell. Scientists are consistently experimenting to see what internal maps birds follow. So far there are a couple of theories.
Birds decide which direction to approach based on smell, creating a map of odors that provide directional guides. Evidence suggests that olfactory navigation extends to 310 miles. Another theory suggests that birds can sense tiny changes in the magnetic field as they approach the poles and fly away from the equator, which tells them the latitude. The third theory says that birds use a sun compass, indicated by the position of the sun, and a star compass for songbird species that migrate at night, who recognize star patterns and the tilt and rotation of the night sky as navigational clues.
The next time you see a V-shaped flock, you can begin to ponder the many generations it took to make that flight possible.
For more on birds, check out the Pocket Ranger® Fish and Wildlife Apps available in New York, Alabama, Wisconsin, Georgia, Nebraska, and New Jersey. The apps provide bird descriptions, distribution areas, and habitat information, along with features like GPS mapping, a built-in compass, and distance indicator to help plan your next birding adventure.