Why do geese honk when they migrate?

Thanks to Viola Ross-Smith for the answer!

James - Thanks for the question, Rick. Native to North America, Canada Geese migrate South in the Winter and North in the summer. They have been known to fly as high as 9km in the sky in that striking V shaped formation, and you’re right to bring up energy expenditure, because that’s the exact reason the bird at the point of the ‘V’ rotates throughout the journey, as it takes the most effort to fly in that position.

So why go to the trouble of all this honking? Surely, there's a method to the madness? Here’s Viola Ross-Smith from the British Trust for Ornithology…

Viola - Thanks James. The Canada Geese are honking to maintain contact with each other. This is especially important when they are flying in formation, which saves energy expenditure in the flock overall. The honking helps each goose communicate its position, and coordinate with the other geese in the V when they shift position. So the energy expenditure of the honking itself is outweighed by the energy they save from the formation flight. Individuals can also use the calls to warn the rest of the flock about an approaching predator.

James - Clever. Is this something other migratory birds do as well?

Viola - Migratory flight calls are common in passerine or ‘perching birds,’ (think Redwings migrating overhead at night in autumn) but their behaviour is much less well understood, and these birds aren't flying together in V formations. There was a study from North America a few years ago showing that passerines of different species with more similar nocturnal migration flight calls follow more similar migratory routes and destinations, so in this case the flight calls might help individual birds to remain on track. Again, even though the calling itself takes energy, it is less energetically costly than getting lost and not reaching your destination at all (and quite probably dying as a result).