January 3, 2015
Humpback whales sound “dinner bell” when hunting at night
Eric Hopton for redOrbit.com - Your Universe Online
Do humpback whales “sing for their supper”?Communal behavior among humpback whales (Megaptera novaeangliae) is well observed. Humpbacks demonstrate an amazing degree of collaboration when cooperating in groups to corral their prey near the surface of the ocean. To study this type of communal feeding and collaboration at the bottom of the sea has proved to be a much harder task for marine biologists. But biologist Susan Parks, assistant professor of biology in the College of Arts and Sciences at Syracuse University, has been carrying out an intensive study of these unique deep water feeding behaviors.
Professor Parks, along with a consortium of other researchers, has demonstrated that communal feeding tactics do occur at the sea bottom and that these giant creatures depend the use of specific auditory cues to maintain contact and share information as they scour the depths of the ocean searching for their prey.
Previous studies have provided clear evidence of social learning in the transmission of specific population level traits in humpbacks. These behaviors include complex singing and stereotyped prey capturing behavior like the corralling technique. Although these group foraging techniques are well observed, there has been little research into how individuals coordinate behaviour in these groups.
Biologists have always struggled to understand how humpback whales find their prey in the darkness of the deep ocean. This latest research has shone some light into that darkness. It seems that humpbacks use acoustic cues to cooperate with each other when feeding on bottom prey, as well as at the surface.
Parks is a specialist in marine science and acoustic communication. She recently published her findings (“Evidence for acoustic communication among bottom foraging humpback whales,” 2014) in the December issue of Scientific Reports. The study was co-authored by researchers at Moss Landing Marine Laboratories, Oregon State University, Gerry E. Studds Stellwagen Bank National Marine Sanctuary and the Whale Center of New England.
Parks and her multi-institutional team spent ten years observing and studying humpback feeding patterns in the Gerry E. Studds Stellwagen Bank National Marine Sanctuary, off the Massachusetts coast. The biologists used tags deployed on 56 whales. The tags were fitted with special underwater recording devices to track the whales and collect data which would help the biologists discover how specific acoustic sounds might correlate with successful seafloor feeding. Analysis of the data revealed a “novel broadband patterned pulsed sound” produced by humpbacks engaged in bottom-feeding. The research team referred to the pulses as a "paired burst" sound. The paired burst sound production was associated exclusively with bottom feeding in low-light conditions, “predominantly with evidence of associated conspecifics nearby suggesting that the sound likely serves either as a communicative signal to conspecifics, a signal to affect prey behaviour, or possibly both.”
The decade long study found that humpback whales do indeed use these “tick-tock” pulse noises when they hunt in groups at night in the almost total darkness of deep water. But, when foraging alone, they remain silent.
A favorite food of the humpback when deep water foraging, is the sand lance, an eel-like fish that buries itself in the seabed sand. Parks believes that the whales use vocal sounds to help flush the sand lance out the sand. The “tick-tock” sounds may also be a kind “come to dinner” bell for other whales in the vicinity during late-night foraging.
“Hints of behavior suggest that other whales who overhear the sounds are attracted to them and may eavesdrop on other whales hunting for food,” said Parks.