The researchers found as small crickets of the subfamily Trigonidiinae, living in the tropical forests of Central America, fleeing from bats. According to the article in the journal Philosophical Transactions of the Royal Society B, these insects are not trying to detect ultrasonic signals of bats on the background of night noise, and include a protective reaction in response to any ultrasound, reaching a certain volume. The presence of this threshold allows to ignore about the threat of the singing grasshoppers or votes of bats that are too far away.
Bats are one of the most dangerous enemies of the night insects. To protect themselves, the latter had to develop a number of adaptations, for example, to learn to listen to ultrasonic signals that bats use while hunting. Unfortunately, they are not always easy to distinguish from background noise, especially in tropical forests, many inhabitants of which make loud noises at night.
A team of researchers led by Heiner Römer (Heiner Römer) from Graz University figured out how to solve this problem of small crickets of the subfamily Trigonidiinaepeoples of the tropical forest on the island of Barro Colorado in the Panama Gulf. These insects are distinguished by an unusual method of protection from the bats: if an ultrasonic signal finds a cricket during the flight, he stops and falls. This tactic allows you to quickly escape from a predator, but a false alarm is very expensive from an energy point of view.
The researchers conducted a series of behavioral experiments with 36 caught crickets. Insects were placed inside the container where they could fly freely, and then included them ultrasonic signals of bats Saccopteryx bilineata and singing a few local species of grasshoppers. It many grasshoppers are considered to be the main source of background noise that interferes with other insects of tropical forest to hear bats.
Analysis of the results showed that the protective response of crickets is activated only in response to ultrasonic signals to a volume above 80 decibels. For comparison, most other insects, are able to eavesdrop on the bats, this threshold is lower from 40 to 80 decibels.
According to the authors, increased reaction threshold — adjusting to life in noisy rain forest. It allows you to ignore not only most of the singing grasshoppers, but also bats, which are at a distance on seven meters — that is too far to locate a cricket with echolocation and attack him.
If necessary, bats can reduce the frequency of their cries. For example, in a recent experiment pale koperasi (Phyllostomus discolor) change their vote in exchange for a reward in the form of bananas. At least one individual is not simply acting by trial and error, and would imitate the voice that the researchers lost of dynamics.
Sergey Knee High