b'Biological geomagnetic field sensingFeatureBiological geomagnetic field sensingRoger Henderson rogah@tpg.com.auIntroductionGeophysicists are familiar with physical magnetometers that sense the Earths geomagnetic field, but there are also other sensors of the geomagnetic field which are biological\x08 For at least the past 50 years a particular behaviour of a wide range of animals has been observed, suggestive of an ability to sense Earths geomagnetic field (hereafter abbreviated as GMF)\x08 This can involve orientation to the field direction, and its use in migratory navigation\x08The biophysical mechanism for how such sensing is relayed to an animals brain is still a matter for research\x08 Also, until 2019 there has been no verifiable evidence of this sensing of theFigure 1.The directions of pigeons no longer have the heading of home GMF in humans\x08 However, a paper published in March 2019after crossing magnetic anomalies shown in the magnetic profiles of the area (see following) claims to have found a possible way in which(from Kirschvink et al, 1985).this ability can be true of humans\x08 In general, there has been a recent resurgence in papers on this subject which is generallyfield, showing that they use the field for orientation\x08 Monarch known as magnetoreception1\x08 butterflies, in particular, have been shown to react in this way\x08The observations In 1975 in a particular type of bacteria now well known as magnetotactic bacteria was described\x08 Biologically developed One way that sensing the GMF is apparent is that many animalsmagnetic material, called magnetosomes, is enclosed in the display an ability to navigate to their destination or return homebacterias cells\x08 These magnetosomes align with the GMF as if they possess a compass\x08 These include homing pigeonsand the alignment can be changed in the presence of a bar (returning from 100 kms away), bees, trout, salmon, monarchmagnet\x08 Figure 2 shows similar magnetosomes from the butterflies, marine turtles (the latter two over global distances)sockeye salmon\x08and more\x08 This can be at night, so navigation is not dependentSensing the field in ways other than directly with on sunlight alone\x08 magnetosomes includes the very first observation more than 50 This involvement with the GMF is, in one way, shown whenyears ago in India that termites align their mounds in the GMF the field is disturbed, as has been observed with homingdirection\x08pigeons whose headings are erratic during magnetic storms (see Figure1)2\x08 Also, in the presence of an artificial field in theWhat is the sensor?laboratory some animals track the change in direction of the As to the nature of the sensor involved in these situations, two main theories have been proposed for some decades\x08 One 11\x08 A small selection from a great number of references are; relates to the magnetically responsive material found to exist Wikipedia: Magnetoreception (Up-dated in 2019) with 72 references;in most animals including in the beaks of birds, the noses of Wiltschko, F\x08 R\x08 & Wiltschko, W\x08 2012\x08 Chapter 8 - Magnetoreception\x08 \x08fish, and the brains of whales and dolphins\x08 Bees retain such In Carlos Lpez-Larrea (ed) Sensing in Nature\x08 Advances in Experimental Medicine and Biology\x08 739\x08 Springer\x08 doi:10\x081007/978-1-4614-1704-0 ; andmaterial in their abdomen, while butterflies have it in their more amusingly, Nicholls, H\x08, 2016, Animal Magnetism\x08 New Scientist, thorax\x08 Monarch butterflies, which migrate thousands of 17-31 December, 44-46\x08 kilometres, have substantially more magnetic material than 2Pigeon racers know not to hold meetings when the GMF is disturbed\x08 other butterflies\x08FEBRUARY 2021 PREVIEW 34'