Every spring and fall you can’t help but marvel at the sight of flocks of migrating birds as they head south for the winter, or back here where they spend the summer months making babies that will take up the return journey later that same year. But have you ever stopped to wonder how they’re able to navigate over such great distances without getting lost? The answer is a mix of mechanisms, including sight and smell, along with others that that scientists are still trying to fully understand.
Follow the sun and stars
Long before early humans figured out they could navigate by the sun and stars, various wildlife species were using those celestial tools to travel around. Scientists had long suspected that birds were using the sun and stars to navigate but it wasn’t until the early 1950s when a German biologist named Gustav Kramer conducted a test using mirrors to trick starlings into heading in the wrong direction that the theories were proven. Later research determined that birds note the position of the sun in relation to their internal circadian clock to determine the direction they’re heading, a process dubbed the “time-compensated sun compass.”
Other researchers have shown that birds also use the stars to guide them on their journey. In the northern hemisphere, the North Star is their primary beacon.
It’s believed that the moon’s relatively rapid passage across the sky along with its occasional “disappearance” during a new moon negate it’s use as a guiding light for navigation.
Birds aren’t the only creatures that use the sun as a compass. Inspired by the research into bird navigation, in a ground-breaking report published back in 1957 biologists moved box turtles to an unfamiliar location. On clear days, the turtles were quickly able to orient themselves and started heading in the direction of home. But if the skies were cloudy, the turtles were disoriented. Other researchers concluded that other reptiles, including the plains garter snake, also use solar navigation.
Memorize the map
Most migratory birds avoid travelling over large stretches of open water during migration and, instead, follow the contours of the shoreline as they travel around the Great Lakes, funnelling through popular bird-watching areas such as the Niagara Peninsula and around Kingston, Ont.
But it seems that various species also use memory to find their way. In the 1990s, a German research team published a paper entitled, “Can honey bees count landmarks?” After a series of tests using frequently repositioned yellow tents they concluded that, yes, they could.
David Sherry, a biologist at Western University, believes that black-capped chickadees also use their memories to find food caches that they stored away months earlier. Food caching birds have a larger hippocampus, a part of the brain key to memory development and retention, than those that do not store food.
And a study on white-crowned sparrows found that adults were able to course correct if they are moved thousands of miles away in closed containers, while juveniles were not, suggesting that the adults had memorized the route from a, well, birds’-eye perspective.
Birds supplement their solar cues with the ability to detect the Earth’s magnetic field, using the intensity at the poles to guide them north or south.
Other animals use the magnetic fields as well. A Czech research team discovered that red foxes consistently attack prey hidden under the snow by leaping in a roughly northeastern direction, concluding that they orient themselves by using a combination of listening and sensing the magnetic poles to track their targets.
American eels are another species that heads south to breed, making their ways from the Great Lakes all the way to the Sargasso Sea in the Atlantic Ocean, only to head back decades later. Researchers concluded that the eels also detect the planet’s magnetic field and use that as their primary navigation tool.
The sniff test
Every dog owner knows that canids “mark” their territory by urinating on trees and other objects. But wolves and foxes also have scent glands in the pads of their feet and on their tail that leave a trail that fellow pack members can follow.
Similarly, a 2014 paper in the Journal of Zoology showed that female polar bears leave scent trails for males to follow them across the ice when they’re in estrus.
Various fish species, including salmon and trout, use olfactory bulbs in their heads to help them sniff their way upstream to the tributaries where they were born for spawning.
Finally, researchers also suspect that scent plays a role in the Monarch butterfly’s epic migration to Mexico, using the smell of the oyamel pine forest on the final leg of their journey to hone in on their overwintering grounds.