It's not just humans who learn from their elders – it turns out the endangered whooping crane can pass wisdom down the generations as well. The discovery could change the design of pioneering programmes to save the birds.
The eastern US population of whooping cranes (Grus americana) spend summers in Wisconsin and winters in Florida. Conservation efforts to reintroduce the endangered species into the wild have shown scientists that it's not just an inner GPS that helps the cranes navigate their seasonal migrations. The birds play a game of follow the wisest leader.
"The learning process of this migration happens over many years and it's something that is culturally learned," says Thomas Mueller of the University of Maryland, who analysed data on whooping-crane flight gathered via radio, and satellite among other methods. "The knowledge itself doesn't just exist."
At the US Geological Survey's Patuxent Wildlife Research Center in Wisconsin, whooping cranes are raised from birth by researchers dressed as cranes, a ploy which tricks the birds into thinking the scientists are their parents. This "imprinting" means the team can later teach the young birds to fly south for the winter by leading them in ultralight aircraft. The birds return unaided to Wisconsin in the spring.
To tease out which parts of this migration are driven by inherited instinct versus guidance, Mueller monitored the age, size and kinship of all birds on flights that were not led by a human in an ultralight, between 2002 and 2009. He found that one factor consistently improved the accuracy of a group's migration path – the age of the oldest individual bird in that group. The team found that the older the crane, the less it deviates from its straight-line migratory path, and this influences the migration of the entire group.
Inexperienced flight groups where the oldest members are just 1-year-old deviated 76 kilometres from a straight migration path, while groups containing 8-year-old cranes deviated only 46 kilometres. A straight path is the most sensible one, because it requires less energy.
Though they expected closely related birds to perform similarly – proving that the ability to follow a straight migratory path is inherited - they found no evidence of this.
"That doesn't mean genetics doesn't play a role, but we didn't find that birds migrate similarly if they're closely related to one another," says Mueller.
Over the past 60 years, conservation efforts have brought global whooping crane numbers up from 16 to over 500, and successful migration is key to the species' survival. The average age of this whooping crane population is increasing and as generations of birds learn these migratory paths, their numbers may continue to rise.