After a long-distance trip under the polite, if slightly repetitive instruction of your favorite GPS app, nothing is worse that being told how to navigate your own neighborhood.
Migratory birds that can sense the planet's magnetic field might experience a similar irritation over being micromanaged. Researchers from the University of Western Ontario in Canada and Bowling Green State University in the US have found they can lilterally switch off their neurological navigation aid when no longer in need of it.
The research looked at white-throated sparrows (Zonotrichia albicollis) and found that they were able to activate a particular part of their brain when they needed to migrate, and put it back into a dormant mode while resting at stopover points.
This 'cluster N' brain region has previously been identified as being important to avian navigation, but it hasn't been clear precisely how it was used across species, or if it activates and deactivates automatically based on daily or seasonal cycles.
"This brain region is super important for activating the geomagnetic compass, especially for songbirds when they migrate at night," says psychology graduate student Madeleine Brodbeck from the University of Western Ontario in Canada.
"Almost all previous work on this specific brain function was done at one lab in Europe, so it was great to replicate it in a North American bird like the white-throated sparrow."
The birds were analyzed in three groups in the lab: daytime, nighttime resting, and nighttime migratory restlessness. That restlessness was determined by increased activity, such as wing whirring and perch hopping.
Through an examination of the brains of the birds separated into these three groups, cluster N activation was found to be associated with migratory restlessness, rather than whether it was day or night. The more restless the birds, the more active cluster N neurons appeared to be.
In other words, it's not a part of the brain that's switched on automatically during the migration season – or even at night. Previous studies suggest that cluster N is always enabled at night, but that wasn't the case here.
It adds to our understanding of how birds and other animals use the planet's magnetic field to find their way, which could rely on something as simple a gentle tug on magnetic particles or something as complex as a nudge of quantum chemistry.
"Magnetic fields are really fun to think about because they're invisible to humans," says Brodbeck. "We can't see them or sense them, but most animals perceive them in some way."
"For birds, using Earth's magnetic field to know if they're going towards a pole or towards the equator is obviously really helpful for orientation and migration. It's incredible that they can activate their brain in this way, and we can't."
Besides teaching us more about how birds migrate and find their way around the world, it's another reminder that our cities can potentially interfere with the natural processes going on around us.
If we know how animals are living their lives, we've got a better idea of how to stay out of their way or help them find safe passage. The researchers suggest there's still a lot more about the cluster N part of bird brains that can be discovered in future studies, such as how weather cues or fat stores might impact its activity.
"Birds don't just use their magnetic compass," says psychologist and biologist Scott MacDougall-Shackleton, from the University of Western Ontario. "We know they pay attention to the Sun and the stars as cues too. And we also know that things like lights at night, or windows in buildings, and all these things that we put in the world disrupt their migrations."
"This type of basic research informs us and lets us know the full suite of ways that animals perceive the world when they're migrating and what we as humans need to do to minimize our impact."
The research has been published in the European Journal of Neuroscience.