Imagine yourself visiting a big bustling city for the first time. You’ve spent all day wandering around, trying new foods, visiting novelty shops, and as the sky begins to darken you come to a dreadful realization. You are lost and, worst of all, your phone is totally dead. Gulp.
How do you find your way back to your hotel? You think about asking for directions, but immediately remember than you’re in a foreign country with a language that you don’t speak. What would you do?
In the wild, animals are constantly facing similar yet much more dire situations (well, except for the whole dead cell phone bit). Critters frequently venture away from home in order to find mates, food, and shelter—among many other things. Eventually, they need to find their way back—a behavior known as ‘homing’. It’s how Fluffy the cat and Sparky the dog can somehow roam miles away from home while always managing to find their way back. But, how exactly do they do it? Thanks to the efforts many researchers, we now know some really cool things about homing behaviors like:
- Sea turtles and salmon use a combination of olfaction (smell) and sensing of the Earth’s magnetic field to find their way home.
- Fiddler crabs count their steps and track the distance of each step to calculate how far they’ve travelled from home—a process known as path integration. Try doing that with four pairs of legs!
Take two different species, move them far away from home, and see which one is better at finding their way back. Who would win and how would you measure their performance? Here are three important metrics:
1) Success or failure?
-The first true test is whether they can find their way back at all.
-How long did it take? Minutes…hours… days?
-Did they get lost multiple times or did they travel in a straight line directly to their destination?
These are the questions that researchers Kamran and her colleagues asked in a recent study, where they compared homing ability in two crayfish species. In the wild, one species (Creaserinus fodiens) spends most of its life building and living in large elaborate burrows (let’s call them ‘miners’). The other species (Faxonius rusticus) builds smaller, simpler burrows and spends much of its time roaming around outside (let’s call them ‘hikers’). Between the two species, does one have a better homing instinct than the other?
To answer this question, researchers created artificial arenas with burrows and treadmills and, on separate occasions, placed ‘miners’ and ‘hikers’ into the arena. Crayfish were allowed to acclimate to their new burrow, after which a piece a food was placed in the arena to coax the animal away from the burrow. Once the crayfish finished eating, the researchers measured how long it took them to find their way back home—but there’s a twist. In one set of experiments, there was no disruption to their homing behavior (control group). In the other set of experiments, however, the treadmill in the arena was turned on to move the crayfish farther or closer to their destination (experimental group). That way the crayfish couldn’t simply remember how many steps they took away from their burrow to find their way back.
What Did They Find?
When it came to the control group with no treadmill movements—and therefore no disruption of the homing behavior—‘miners’ and ‘hikers’ were equally successful in returning to their burrows in a similar amount of time.
However, the success rate of both species plummeted in the experimental group with treadmill movements. Those that did manage to find their burrows took longer and did so inefficiently by travelling more in a squiggly line than a straight line. In other words, many of the crayfish were lost. But, still, many of them eventually found their way back. In fact, ‘hikers’ were better at improvising and finding their way back than ‘miners’. After getting confused by treadmill displacement, ‘hikers’ were much more successful than ‘miners’ (60% versus 20% success rate). Not to mention that ‘hikers’ found their way home while making fewer mistakes.
What does this mean? Kamran and her colleagues think that these differences between the ‘miners’ and ‘hikers’ are related to their behavioral ecology of burrowing. ‘Miners’ spend more time in their burrows whereas ‘hikers’ often leave their burrows to make long foraging trips. Interestingly, prior research has found that idiothetic cues (internal information) like step counting become less reliable over longer distances. Thus, one possibility is that ‘hiker’ crayfish are better at using allothetic cues (external information) like landmarks to perform their homing.
Yordano Jimenez is an NSF GRFP fellow at Brown University studying muscle function in suction-feeding fishes.