Animal echolocation

The term echolocation was coined by 1944 by the American zoologist Donald Griffin, who, with Robert Galambos, first demonstrated the phenomenon in bats.

[9] In 1912, the inventor Hiram Maxim independently proposed that bats used sound below the human auditory range to avoid obstacles.

[11][12] Echolocation in odontocetes (toothed whales) was not properly described until two decades after Griffin and Galambos' work, by Schevill and McBride in 1956.

[13] However, in 1953, Jacques Yves Cousteau suggested in his first book, The Silent World, that porpoises had something like sonar, judging by their navigational abilities.

[28] The major advantage conferred by an FM signal is extremely precise range discrimination, or localization, of the target.

This ability is due to the broadband sweep of the signal, which allows for better resolution of the time delay between the call and the returning echo, thereby improving the cross correlation of the two.

The 3D localization abilities of the broadband signal enable the bat to do exactly that, providing it with what Simmons and Stein (1980) call a "clutter rejection strategy".

This means that the bat can get an almost continuous stream of information – essential when objects are close, because they will pass by quickly – without confusing which echo corresponds to which call.

First, the greater working range of the call allows bats to detect targets present at great distances – a common situation in open environments.

[37] Echolocating bats generate ultrasound via the larynx and emit the sound through the open mouth or, much more rarely, the nose.

Bats may estimate the elevation of targets by interpreting the interference patterns caused by the echoes reflecting from the tragus, a flap of skin in the external ear.

The adaptation of echolocation calls to ecological factors is constrained by the phylogenetic relationship of the bats, leading to a process known as descent with modification, and resulting in the diversity of the Chiroptera today.

[50] These moth adaptations provide selective pressure for bats to improve their insect-hunting systems and this cycle culminates in a moth-bat "evolutionary arms race".

Many of these neurons are specifically "tuned" (respond most strongly) to the narrow frequency range of returning echoes of CF calls.

This short duration of response allows their action potentials to give a specific indication of the moment when the stimulus arrived, and to respond accurately to stimuli that occur close in time to one another.

[59][60] Suga and his colleagues have shown that the cortex contains a series of "maps" of auditory information, each of which is organized systematically based on characteristics of sound such as frequency and amplitude.

Throughout the middle and late Eocene periods (49-31.5 million years ago), archaeocetes, primitive toothed Cetacea that arose from terrestrial mammals, were the only cetaceans.

[66] By the late middle Eocene, acoustically isolated ear bones had evolved to give basilosaurid archaeocetes directional underwater hearing at low to mid frequencies.

[66][67][68] These events encouraged selection for the ability to locate and capture prey in turbid river waters, which enabled the odontocetes to invade and feed at depths below the photic zone.

[67][69] The family Delphinidae (dolphins) diversified in the Neogene (23–2.6 million years ago), evolving extremely specialized echolocation.

Prestin, a motor protein of the outer hair cells of the inner ear of the mammalian cochlea, is associated with hearing sensitivity.

[72] Cldn14, a member of the tight junction proteins which form barriers between inner ear cells, shows the same evolutionary pattern as Prestin.

Cranial telescoping (overlap between frontal and maxillary bones, and rearwards displacement of the nostrils[74]) developed first in xenorophids.

[76] Extant odontocetes have asymmetric nasofacial regions; generally, the median plane is shifted to the left and structures on the right are larger.

[75] Thirteen species of extant odontocetes convergently evolved narrow-band high-frequency (NBHF) echolocation in four separate events.

For all sonar systems, the limiting factor deciding whether a returning echo is detected is the echo-to-noise ratio (ENR).

The ENR is given by the emitted source level (SL) plus the target strength, minus the two-way transmission loss (absorption and spreading) and the received noise.

In cluttered habitats, such as coastal areas, prey ranges are smaller, and species such as Commerson's dolphin (Cephalorhynchus commersonii) have lowered source levels to better suit their environment.

[82] Echoes are received using complex fatty structures around the lower jaw as the primary reception path, from where they are transmitted to the middle ear via a continuous fat body.

[85][86] Terrestrial mammals other than bats known or thought to echolocate include shrews,[87][88][89] the tenrecs of Madagascar,[90] Chinese pygmy dormice,[91] and solenodons.