Roman siege engines BC, and surrounded by Roman fortifications. As was standard siege technique at the time, "ballistae" were placed up in the towers with other soldiers armed with either bows or slings. The onager was a post-classical Roman siege engine, which derived its name from the kicking action of the machine, similar to that of an onager (wild ass). It is a type of catapult that uses torsional pressure, generally from twisted rope, to store energy for the shot. The onager consisted of a frame placed on the ground to whose front end a vertical frame of solid timber was rigidly fixed;
Animal communication individual. The altered signal provides information that can indicate food, predators or conspecifics. Because the sender and receiver are the same animal, selection pressure maximizes signal efficacy, i.e. the degree to which an emitted signal is correctly identified by a receiver despite propagation distortion and noise. There are two types of autocommunication. The first is active electrolocation found in the electric fish Gymnotiformes (knifefishes) and Mormyridae (elephantfish) and also in the platypus ("Ornithorhynchus anatinus"). The second type of autocommunication is echolocation, found in bats and toothed whales. There are many functions of animal communication. However, some have been studied in