Sitting on a beach facing the sea, it might seem unusual to spot one of the world’s largest animals swimming in shallow coastal waters 30 feet deep. But each winter, female southern right whales migrate thousands of miles to bay habitats to give birth and care for their young. So why do they choose such shallow nurseries that can be in dangerous proximity to human activity and where the food supply is scarce?
While researchers have speculated that whales up to 50 feet long choose these spots due to the lack of predators and warmer, calmer waters, a team of biologists from the Bioacoustics Lab and Behavioral Ecology from Syracuse University recently discovered a potential new pattern. They hypothesize that shallow, sandy, near-shore waters are a prime location for whales to give birth and raise their young because these areas have reduced acoustic propagation, meaning vocal signals do not travel. far away at these sites, allowing mother whales to communicate with nearby calves, unheard by predators in the distance.
Since questions remain as to why baleen whales migrate such long distances each year, the research team says their findings shed new light on their migratory behavior. Understanding habitat use and selection also allows researchers to better target conservation and management efforts, which is essential for endangered whale species like the right whale in the North Atlantic.
Authors Julia Zeh and Julia Dombroski, both PhDs. candidates in biology at the College of Arts and Sciences (A&S), and Susan Parks, associate professor of biology and principal investigator of the bioacoustics and behavioral ecology laboratory at A&S, collected data from three nurseries on three continents in the southern hemisphere (South America, Africa and Australia) where southern right whale nurseries are often observed. In their article published in Royal Society Open Sciencethey found that the depth at which right whale mothers and calves are often observed has the most limited acoustic detection range for their calls.
“Animals that communicate using sound must balance the need to be heard by their target audience against the risk of being overheard by prying eyes such as predators,” says Zeh.
Modifications of sound production behavior to reduce detectability by eavesdroppers are known as acoustic encryption. Southern right whales have commonly used three forms of acoustic encryption to avoid predators: reduced call amplitude; use signal frequencies that are difficult for eavesdroppers to detect and/or locate; and reducing or completely stopping the production of acoustic signals, effectively becoming silent to avoid detection.
In their paper, the team proposes a fourth method of acoustic encryption centered on the habitat choice of southern right whales.
“We found that southern right whale mothers and calves spend time in specific places where they can hear each other, but other animals cannot hear them,” says Zeh. “These results follow some interesting recent papers that recorded silent calls, or essentially whispers, from mothers and right whale calves.”
Future research will aim to determine to what extent a habitat selection approach may be common to acoustic crypsis.