Many birds embark on remarkable journeys across continents, and a surprising number of them choose to travel under the cloak of darkness. While it might seem counterintuitive for birds to fly when visibility is low, this unique approach offers several advantages.
Why Many Birds Choose Night Migration
Migrating at night provides birds with several distinct advantages related to safety, energy conservation, and environmental conditions. Flying under the cover of darkness helps birds avoid many of their daytime predators such as hawks and falcons. These predators are less active at night, allowing birds to travel with reduced risk.
Nighttime temperatures are generally cooler than during the day, which is beneficial for birds engaged in strenuous, long-distance flights. The physical exertion of migration generates a lot of body heat, and cooler air helps birds dissipate this heat and prevent overheating. This temperature regulation allows them to conserve energy, making their arduous journeys more efficient.
The atmosphere also tends to be calmer and more stable at night, with less turbulence compared to daytime. This smoother air reduces the energy birds need to expend to maintain a steady course, which is especially helpful for smaller species like warblers that do not fly very rapidly. By migrating at night, birds can dedicate their daylight hours to foraging and resting, which is essential for replenishing the energy reserves needed for their demanding travels.
How Birds Navigate in Darkness
Birds possess remarkable navigational abilities that allow them to find their way across vast distances in darkness. One primary method involves celestial navigation, where birds use the patterns of stars and the moon as a compass. Some species can orient themselves using a “star compass,” learning direction from star patterns around Polaris, the North Star.
Birds also have an internal “magnetic compass” that enables them to detect and utilize the Earth’s geomagnetic field for orientation. This allows them to perceive magnetic fields, discerning north and south even in low light. A special eye protein in birds may enhance their ability to see magnetic fields in dim light.
The combination of celestial cues and sensitivity to the Earth’s magnetic field provides a robust navigational system for nocturnal migrants. This multi-faceted approach ensures they can maintain their migratory paths accurately over thousands of miles.
Common Night Migrants and Their Journeys
Common nocturnal migrants include many songbirds such as warblers, thrushes, vireos, sparrows, and orioles. Other groups, like cuckoos and many shorebirds, also participate in these nighttime movements.
These small birds cover distances, often traveling thousands of miles between their breeding and wintering grounds. For instance, the Arctic Tern undertakes a round trip of more than 49,700 miles between the Arctic and Antarctica. Another impressive example is the Bar-tailed Godwit, which can fly almost 7,000 miles non-stop, a journey that takes approximately eight days without stopping to eat or rest.
Millions of birds participate in these nightly migrations during peak seasons, creating vast aerial movements that are largely unseen by human eyes. Scientists study these nocturnal movements using various methods, including radar, which detects the birds as they fly, and acoustic monitoring, which records their distinctive flight calls. Banding birds also provides data on their routes and destinations, contributing to our understanding of these incredible journeys.