17 Mar ALL ABOUT MIGRATION
The word migration comes from the Latin word migratus, and it means “to change” geographic locations seasonally. Migration peaks in spring and fall. When birds migrate depends on many factors, including bird species, migration distance, travel speed, route and climate. Before migrating, many birds enter a state of hyperphagia, a change in hormone levels that causes them to put on fat to increase their body weight. This fat is energy for the trip. Some species may double their body weight prior to migration.
During the day, hawks, swifts, swallows and waterfowl migrate. Songbird species migrate at night to avoid the attention of migrating predators such as falcons and hawks. The calmer, cooler air at night can make their migration more efficient. The daytime migrants use the solar thermal currents to fuel them.
The nocturnal moving birds use the stars for navigation as well as wind patterns and landmasses to guide them to the same locations each year. The earth's magnetic field also plays a part in bird migration. Some passerines fly 15 - 600 miles in a day; some have stop overs for refueling.
Trans-oceanic migrants - ones whose route crosses an ocean – may be airborne up to 100 plus hours at a single time until they encounter land or a vessel. Long-range migratory birds have longer, more pointed wings than non-migratory species or birds with short migrations. The wing structure is more aerodynamic, allowing for an efficient flight.
Migrating birds travel at speeds ranging from 15 - 50 miles per hour. Flight pattern and prevailing winds can increase or decrease their speed. The round-trip migration of the Arctic Tern is roughly 22,000 miles - the longest recorded migration of any bird on the planet. They get no free upgrades or bonus travel points either...
Migrant birds face perils along the way, including window collisions, confusing lights that can disrupt their navigation [both of which I've mentioned in earlier updates] and predation along their routes. This year's youngsters are at great risk since they're inexperienced travelers. They can also face habitat loss upon arrival at their destinations.