Fear can induce silence. In the world of wild nature, the same thing happens. The struggle for survival modifies the behavior and physiology of the species. Especially those that have the role of prey. This may occur even if encounters with predators are rare. The silent zither cetaceans are a good example.
The fear of killer whales
A team led by Natacha Aguilar de Soto analyzed data from 26 individuals of two species of zifids. It is a family of jagged cetaceans. Those who equipped with sensors that tracked the depth to which they swam, the inclination of their dives and the sounds they emitted during these. The study was called Fear of Killer Whales Drives Extreme Synchrony in Deep Diving Beaked Whales. It is published this week in the journal Scientific Reports.
The authors observed that these animals, also known as Blainville zyphids and Cuvier's calves, -Mesoplodon densirostris and Ziphius cavirostris respectively – they carried out their deep dives in a coordinated manner. They use their senses of echolocation (the use of sound to probe their surroundings). Thus they detect their prey.
Soon came the surprise for scientists. It is known that its main predators are killer whales, who attack them in shallow water. They noted that by emerging into that area, where they are vulnerable, both species greatly limited the sound signals. They also extreme their synchronization in the swim. It is a behavior that has not been observed in other whales that dive deep.
Let's synchronize clocks … and voices
Both species began their vocalizations at an average depth of 450 meters. It was before continuing to descend in search of their prey individually. Later they met in a group at an average depth of 750 meters. Then they silently ascended to the surface at a slightly pronounced angle covering a horizontal distance close to the kilometer.
This tactic sacrifices 35% of the food search time. But it reduces the risk of killer whale interception by an order of magnitude. They often keep silent when hunting. The surprise factor provides an advantage when looking for food.
It is likely that these behaviors, based on echolocation, have helped both Blainville's buzzes and Cuvier's calves survive for millions of years. What does this finding suggest? The risk of predation may have been an important evolutionary force that boosted this unique way of diving. As well as the vocal behavior of the silent zifid cetaceans. Something that may also help explain the reaction of both species to the naval sound used by the ships. It is believed to be the main cause for the mass stranding of these animals.