Battle of the Birds: Migration Marathon

citizen science, Eyewire, geese migration, ornithology, Battle of the Birds
Photo by Barth Bailey on Unsplash

It’s the time of year when bird migrations are about to happen again — or already getting underway. A lot of the birds that live in our local habitats will stay the same, but some songs we heard and coats we saw during this season are going to disappear for a while in favor of other guests. Out of 10,000 bird species worldwide, close to 20% of them undertake long-distance journeys like this! So what motivates so many birds to live this nomadic lifestyle, and how do they do it?

Migration can be understood through two basic needs: food and shelter. In latitudes where a winter season takes place, food sources become scarcer during those months for lots of birds, while weather conditions become dangerously cold for what these birds’ typical sources of protection from the elements can withstand. Many birds have evolved to put up with these problems by diversifying their diets or specializing in ways to stay warm; the cost-benefit ratio is better for them than expending the energy to fly thousands of kilometers and risk predation or pathogens on the way. However, migratory birds have found that risk worthwhile, and they’ve evolved in turn.

Typically, when ornithologists talk about where birds go during migration, they talk about the birds’ two different ranges, which are their breeding grounds and their non-breeding grounds. The non-breeding grounds are usually where these birds fly to in autumn; here they relax on their beach towels (metaphorically speaking) and don’t worry about mating. Their breeding grounds are usually where they return in spring once that landscape’s conditions are abundant and safe for raising a brood of babies.

You might now be wondering why birds don’t all just stay in warm, always-summery latitudes! Why wouldn’t they just breed in the tropics and find everything they need there? Well, for one thing, competition with existing tropical birds would be too stiff for all temperate-zone birds to just stay there year-round; migratory birds fulfill their own ecological role in each of their shifting habitats. For another thing, many migratory birds also won’t tolerate a really hot summer any more than they’ll tolerate a cold winter, so they split the best of both worlds. And lastly, not all long-distance bird migration actually goes from temperate zones down to tropical ones. Some birds like the dark-eyed junco live in sub-Arctic Canada during the breeding season, but they visit New England during winter because it’s still a lot warmer than where they came from and they don’t have to make it all the way down to Florida.

Many migratory birds really are marathon flyers, though. One superstar is the Arctic tern, which holds the long-distance record and could just as easily be called the Antarctic tern, migrating between the Earth’s polar regions so that it never experiences polar night. There’s also the short-tailed shearwater, whose migratory path circles half the Pacific Ocean, or the famous albatross family. Most birds who migrate don’t get as intense as these feathered friends, but they still travel a long way, often even in tiny bodies; the ruby-throated hummingbird’s breeding range extends up to Eyewire HQ, but for winter these itty bitty wonders may go all the way to Guatemala.

Many factors go into making these long journeys possible. Here are just a few common adaptations!

  • Daylight-affected hormones: Changes in daylight levels trigger hormonal changes in most migratory birds, signaling their brains to get excited about going somewhere, and signaling their bodies to increase fat deposits as energy reserves. These hormones may also be affected by average temperatures, which may help some species cope with climate change instead of traveling too early or too late for optimal weather conditions.
  • Flying in flocks: The risks of predation by other bird species are mitigated by “birds of a feather sticking together.” Also, the movements of birds’ wings changes the air flow patterns for birds that fly behind them; for instance, geese flying in V-formation conserve 12-20% of the energy they would otherwise need, and they trade off on who has to fly in front to help their fellow geese.
  • Advanced navigation skills: Who needs GPS? Migratory birds’ navigation strategies vary by species but can involve methods like orienting themselves with the sun, aligning themselves with the planet’s magnetic field, and following landmarks below them. Some species even use their sense of smell, contrary to bird stereotypes.
  • Bird elders: Migratory birds’ flocking behaviors have made them highly social species. Even though lots of their navigation happens instinctively, these birds also teach each other what to do. Older members of the flock who are already practiced will show the first-timers how this is done, just like human parents teaching their kids to drive.

Now that you know more about bird migration, how are you feeling about a marathon of our own on Eyewire? Starting at 10:00 AM EST on 2/21, you will have 24 hours to complete one or more cells! Bonus & cell renaming information can be found in your in-game notifications.