In a new study, researchers throw light on humpback whales' little-understood acoustic behaviour while foraging.
They found a previously unknown behavioural flexibility on the whales' part that allows the endangered marine mammals to balance their need to feed continuously with the competing need to exhibit mating behaviours such as song displays.
"They need to feed. They need to breed. So essentially, they multi-task," said study co-author Ari S Friedlaender, research scientist at Duke University's Nicholas School of the Environment.
"This suggests the widely held behavioural dichotomy of breeding-versus-feeding for this species is too simplistic," Friedlaender said.
Researchers from the US Naval Postgraduate School, the University of California-Santa Barbara and Duke tracked 10 humpback whales in coastal waters along the Western Antarctic Peninsula in May and June 2010.
Using non-invasive multi-sensor tags that attach to the whales with suction cups, the researchers recorded the whales' underwater movements and vocalisations as they foraged.
All 10 of the tags picked up the sounds of background songs, and in two cases, they recorded intense and continuous whale singing with a level of organisation and structure approaching that of a typical breeding-ground mating display.
The song bouts sometimes lasted close to an hour and in one case occurred even while sensors indicated the whale, or a close companion, was diving and lunging for food.
Humpbacks sing most frequently during breeding season, but are known to sing on other occasions too, such as while escorting mother-calf pairs along migratory routes.
Though the reasons they sing are still not thoroughly understood, one distinction is clear: Songs sung in breeding grounds are quite different in duration, phrase type and theme structure from those heard at other locations and times.
"The fact that we heard mating displays being sung in late-season foraging grounds off the coast of Antarctica suggests humpback whale behaviour may be more closely tied to the time of year than to physical locations," said Douglas P Nowacek, Repass-Rogers University Associate Professor of Conservation Technology at Duke's Nicholas School.
"This may signify an ability to engage in breeding activities outside their traditional warm-water breeding grounds," Nowacek said in a statement.
The research was published in journal PLoS ONE.
