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Bioelectromagnetism

also make a fgure-eight movement with their posteriors. Te direction of the wagging dance of honey

bee shows the angle between the location of the food and the sun, and the angle is transposed with

respect to gravity. Te speed of turning is said to represent the distance to the food. Martin Lindauer

and Hermann Martin showed that this honeybee dance was afected by geomagnetic feld (Lindauer and

Martin, 1968). When the geomagnetic feld is compensated to ± 4%, misdirection disappears. Te visible

iron-containing granule cells are in the form of magnetite. Later, it was found that there was magnetite

in the abdomen of honey bees that was strongly magnetized laterally. Tey are formed in hydrous iron

oxides. It is thought that the magnetite is formed during the growth from larva to adult, with the mag­

netism being oriented with the geomagnetic feld. Honeybees use this magnetite as a sensor for geomag­

netic feld, and they are thought to use this to determine direction (angle) even when it is cloudy and the

sun cannot be seen. However, this angle is afected by the magnetic feld of 0.1–0.001 μT.

Te other case is the migratory birds. Alexander Teodor von Middendorf suggested that migrating

birds orient along magnetic meridians (1859). Today it means that the migrating birds use a magnetic

compass. Middendorf recorded the places and date of arrival of migrating birds from 1841 to 1854.

Using these data, he drew a number of migratory routes of birds on a map. He referred to it as Isepipteses.

Isepipteses means lines of simultaneous arrival (Al-Khalili and McFadden, 2014). In his report pub­

lished in 1859, he proposed that the migratory birds orientate themselves by the geomagnetic felds.

However, most nineteenth century zoologists had no interest and remained skeptical. It passed over

hundred years since von Middendorf’s suggestion that the migratory birds may solve their orientation

by reference to the geomagnetic feld. From the middle of the twentieth century, the supported experi­

ments about efects of the geomagnetic feld on bird migration have been investigated.

Friedrich Wilhelm Merkel observed the night-migrating birds can orient their orientation without

help of celestial cues and identifed the geomagnetic feld as a key factor controlling bird orientation in

the night. Merkel and Wolfgang Wiltschko published two papers on the discovery of magnetic compass

in the European robin (Merkel and Wiltschko, 1965; Wiltschko and Merkel, 1966). Although magnetic

compass remained still skepticism in the scientifc community, Wiltschko’s discovery that the birds

used geomagnetic feld as orientation compass was the breakthrough and expands the experimental and

theoretical studies of magnetic compass sense of animals including vertebrate, invertebrate, bacteria,

fshes, and birds. Te ability to sense and respond to magnetic stimuli is known for a number of animals

and bacteria. A number of experiments have reported that geomagnetic feld was being used for migra­

tion and orientation (Wiltschko and Wiltschko, 1995).

Tere are three theories as to how animals including birds sense geomagnetism. Te frst one is elec­

tromagnetic induction, which is thought to occur in fshes, but the receptors needed for this mechanism

are not found in birds or other animals. Te second theory has to do with magnetized magnetite, which

was discovered in the 1970s by a magnetotactic bacterium that uses magnetite in its body to move with

the direction of geomagnetic feld. Honeybee, fsh, and birds also have fne crystals of magnetite. Te

third theory is that magnetic sensation in birds and other animals is mediated by biochemical reactions.

In 2002, Ritz et al. have proposed a theory that birds can sense geomagnetism because a light-induced

biochemical reaction occurs in the bird’s eye and cryptochromes, a protein in the retina, act as a magnetic

sensor (Ritz et al., 2000; Timmel, 2004). See other chapters for more discussions on magnetoreception.

Magnetoreception is widespread in the animal kingdom. Tere are lots of behavioral evidence from

many outdoor experiments. A research group from the University of Duisburg-Essen, Germany, has

repeated experiments on how wild animals perceive their surrounding environment and reported inter­

esting results. In response to the question of what cues waterbirds such as ducks and geese fying in

focks at high altitudes, use when landing on the surface of a lake, researcher hypothesized that water­

birds are sensitive to magnetism and that their landing direction indicator follows magnetic feld lines,

and confrmed that they use a magnetic compass for landing (Hart et al., 2013a). Te study showed that

the landing direction indicator of a total of 15,000 birds from 14 species of waterbirds and suggested that

they landed facing north-south in absence of any other common denominator determining the land­

ing direction. More objective and reproducible data are needed. Te relationship between predatory