Nocera and his colleagues obtained recorded antipredator calls made by large aggressive mobs of blue-grey tanagers and black-capped chickadees and played them to birds in the area.
(Related story: "Chickadees Use Complex Calls for Predator 911" [June 23, 2005])
The scientists expected local birds to respond to the tanager calls, since tanagers are found throughout Belize. But they were not certain if migrants would understand this local avian dialect.
When locals and migrants heard the tanager calls, the team found, they responded with agitation and anxiety by repeatedly making calls themselves and changing their positions.
Remarkably they found that migrants also responded to chickadee antipredator calls, even though chickadees are not found anywhere near Belize. Local birds did not respond to chickadee calls at all.
"That migrants would respond to a species' call that they shouldn't expect to hear within 2,000 kilometers [1,242 miles] of where they were came as a big surprise," Nocera said.
Memories
Lauren Benedict, an avian biologist at the University of California, Berkeley, was not involved with the study.
"It's amazing that even a continent away [the birds] remember and react appropriately to danger signals," she said.
"This illustrates the impressive ability birds have to recognize and remember vocal signals," she continued.
(Related story: "Bird Brains Swap Regions for Baby Babbling, Adult Song" [May 1, 2008])
Laszlo Garamszegi, an ecologist at the University of Antwerp in Belgium, also was not involved with the study.
"These findings are a bit similar to what we found with vocal mimicry," he said.
"We discovered that long-distance migrating birds pick up more new sounds than birds which remain local."
