The Science of Bird Migration
The holidays are a season of celebration, cold weather, and often, travel. Human travel may be on hold, or at least ill-advised, due to COVID, but birds have still been migrating en masse. In 2018, the Cornell Lab of Ornithology estimated that 4 billion birds flew from Canada to the US and another 4.7 billion flew from the States to the tropics. Much like humans, both temperature and food are reasons birds travel in the fall and winter. But how do they know when it’s time to go?
(Birds migrating over Dunlin, NC. Photo taken by Walker Golder and found on nc.audubon.org).
Some birds know when it is time to migrate because food becomes scarce or they sense changes in magnetic fields. Other birds have migration-related genes, though oddly enough, these are also sometimes found in nonmigratory birds. They may not pack suitcases, but according to Matador Network, birds do get plumper and load up on energy before heading south. Fluctuating hormones cause these changes, which are often accompanied by behavior changes and molting. While different birds migrate at different times, September through November is the peak migration season for birds in the southeastern US. It appears birds don’t enjoy fall as much as many humans do!
Types of Migration
Just as there are many ways birds determine when to migrate, there are many types of bird migration. Latitudinal, longitudinal, and altitudinal migration are just about self-explanatory: birds move east, west, north, south, or to new elevations. However, birds don’t always follow the same path, and loop migration involves using two distinct routes to take advantage of resources available during trips to and from breeding sites. Some birds have very little structure to their routes. Nomads move in and out of their range erratically based on food and resources. Irruptive birds venture into unusual habitats in search of food and other goodies. For birds, migration is a risky business. Storms can sometimes cause drift migration, which results in large numbers of birds blown off course. One risk for young birds is to be directionally challenged, resulting in reverse migration, the phenomenon of birds becoming confused and moving in the opposite direction of where they should be going. As you can see, bird migration is very nuanced.
Finding Their Way
With so many ways for birds to migrate, how do they determine which way to go? Many navigate using stars and landmarks, hence one reason why birds may return to the same breeding site year after year. Surviving migration is no easy feat; light pollution, predators, food scarcity, and natural disasters are all real threats, and bird mortality is high, especially among first-time migrators. Luckily, some birds have developed adaptive behaviors, such as flying at night to avoid predators. Migratory “rest breaks” are not universal, but they’re also not uncommon. Recent migration research has focused on where birds stop during their journey and how this may impact their survival. Protecting common “rest areas,” such as part of Florida, may turn out to be an excellent bird conservation strategy.
Giving Migrating Birds a Hand
Research on birds’ rest stops is just one example of the scientific study of bird migration. There is also significant work conducted to track birds electronically. Some websites, such as birdcast.info, allow visitors to view migration statistics, watch migration in real-time on a map, and even see predictions of which birds will migrate when and where. This year, Cornell University’s Lab of Ornithology also hosted a virtual migration celebration full of themed lectures and events. Learning about migration is well and good, but hopefully, it will also motivate you to take action to protect birds. Among other things, you can minimize outdoor lights at night and keep cats indoors, especially in the fall. Bird migration is fascinating and complex, with many topics to study and ways to make birds’ transitions smooth!
(Example of a bird migration map from birdcast.com).
Written by: Katrina Thomas. Katrina has a Bachelor of Science degree in Biology from Meredith College and is pursuing an Environmental Educator Certification through EENC.