Sparrows’ navigation skills come with experience

November 14th, 2007 - 8:32 am ICT by admin  
Migrating adult sparrows adjust their flight plan to find their way to their winter nesting grounds even after being thrown off course by thousands of miles, they have found in a study.

But similarly displaced juvenile birds that have not yet made the complete round trip, say the researchers, can only orient themselves southward, indicating that songbirds’ innate sense of direction must be augmented with experience if they are to find their way home.

“This is the first experiment to show that when it comes to songbird migration, age makes a difference. The results indicate that the adult birds possess a navigational map that encompasses at least the continental US, and possibly the entire globe,” said team member Martin Wikelski, an associate professor of ecology and evolutionary biology.

During their study, the researchers fitted a group of white-crowned sparrows with tiny radio transmitters, and tracked their movements.

As many as 30 sparrows were brought to Princeton from northern Washington State, where the birds had been in the process of migrating southward from their summer breeding grounds in Alaska.

Half of the birds were juveniles of about three months in age and had never migrated before, while the other half were adults with the experience of migration.

Upon being released by the researchers, the birds attempted to resume their migration, but both age groups grew disoriented quickly.

“All the birds scattered at first. It was clear they were turned around for a couple of days. But while the adults eventually realized they had to head southwest, the younger birds resumed flying straight southward as though they were still in Washington,” Wikelski said.

Richard Holland, a member of the research team, said that the adult birds recovered their bearings because they possessed an internal map, something the younger birds did not possess.

“These birds need two things to know where they are and migrate effectively: a ‘map’ and a ‘compass’. What we’ve found is that juveniles use their compass, but the adults also use their map,” said Holland, a postdoctoral research associate in Wikelski’s lab.

According to him, birds do not lose the compass as they age, but somehow develop the map, and eventually apply both tools to keep on track during migratory flights.

Scientists have already determined that the compass is based on the sun or the magnetic field, but they have yet to find out where the map comes from.

“It could be the map also derives from the planet’s magnetic field. But there are so many local magnetic anomalies in the Earth’s crust that it’s also possible they are navigating by sense of smell. It sounds crazy, but there’s a lot of evidence that homing pigeons navigate this way, so we need to investigate that idea further,” Holland said. (ANI)

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