Acoustic crypsis is a behavioral adaptation used by animals to reduce detection by eavesdroppers such as predators. This is an especially important tactic for baleen whales because they rely heavily on acoustic signals for communication because these signals propagate well through their aquatic environment. Since acoustic signals can rely messages over long ranges with relative accuracy underwater, theres an inherent increase in their risk of eavesdropping/interception by predators such as sharks and orcas. This is something recent mother’s still nursing their calves are especially aware of because calves are smaller and thus an easier target for predation. Therefore one way these mother-calf pairs can decrease their risk of predation is to decrease their detection using acoustic crypsis.
For North Atlantic right whales, acoustic crypsis can come in two forms: reducing the amount of calls they produce and reducing the amplitude/loudness with which they propagate those calls. A recent study by Parks, Van Parijs, and Nowacek hypothesized that if the calves of North Atlantic right whale mother-calf pairs are in their first three months after birth (when they’re most vulnerable to predation), then the mother-calf pair will exhibit acoustic crypsis. They predicted that mother-calf pairs would show acoustic crypsis behavioral modifications of either reduced calling rates (suppression of signal production), reduced/lower call amplitude, or a combination of both during this time.
Their results were consistent with their hypothesis, providing evidence that right whale mother-calf pairs exhibit acoustic crypsis by reducing the number of higher amplitude calls they produced compared to the juvenile and pregnant whales in the same habitat. These findings were also consistent with a previous study of humpback whale and Southern right whale mother-calf pairs. This suggests that acoustic crypsis is being used by whale mother-calf pairs to minimize the risk of eavesdropping and detection by predators while still allowing for communication between mother and calf over relatively short ranges.
Northern Atlantic right whales are a type of baleen whale that is highly endangered. This research supplies us with more information on how the most vulnerable group within this species evades predation.
Parks SE, Cusano DA, Van Parijs SM, Nowacek DP. 2019 Acoustic crypsis in communication by North Atlantic right whale mother– calf pairs on the calving grounds. Biol. Lett. 15 : 20190485. http://dx.doi.org/10.1098/rsbl.2019.0485