Migratory Eurasian Reed Warblers Can Use Magnetic Declination to Solve the Longitude Problem

Abstract

The longitude problem (determining east-west position) is a classical problem in human sea navigation. Prior to the use of GPS satellites, extraordinarily accurate clocks measuring the difference between local time and a fixed reference (e.g., GMT) [1] were needed to determine longitude. Birds do not appear to possess a time-difference clock sense [2]. Nevertheless, experienced night-migratory songbirds can correct for east-west displacements to unknown locations [3-9]. Consequently, migratory birds must solve the longitude problem in a different way, but how they do so has remained a scientific mystery [10]. We suggest that experienced adult Eurasian reed warblers (Acrocephalus scirpaceus) can use magnetic declination to solve the longitude problem at least under some circumstances under clear skies. Experienced migrants tested during autumn migration in Rybachy, Russia, were exposed to an 8.5° change in declination while all other cues remained unchanged. This corresponds to a virtual magnetic displacement to Scotland if and only if magnetic declination is a part of their map. The adult migrants responded by changing their heading by 151° from WSW to ESE, consistent with compensation for the virtual magnetic displacement. Juvenile migrants that had not yet established a navigational map also oriented WSW at the capture site but became randomly oriented when the magnetic declination was shifted 8.5°. In combination with latitudinal cues, which birds are known to detect and use [10-12], magnetic declination could provide the mostly east-west component for a true bi-coordinate navigation system under clear skies for experienced migratory birds in some areas of the globe.

Magnetic body alignment in migratory songbirds: A computer vision approach

“…magnetic North) is shifted with the use of a 3D coils array (e.g. Lohmann, 1991;Ilieva et al, 2016;Chernetsov et al, 2017). Such experiments usually shift the polarity by 90 deg (Sandberg et al, 1988;Åkesson, 1993, 1994Sjöberg and Muheim, 2016, and references therein), and therefore it would be impossible to verify the effectiveness of a magnetic polarity shift in a bi-axial response.…”

“…In contrast, magnetic orientation has been extensively studied in migratory songbirds in modified so-called Emlen funnels (Emlen and Emlen, 1966), in the past 50 years (e.g. Wiltschko and Wiltschko, 1972;Sandberg et al, 1988Sandberg et al, , 1998Munro and Wiltschko, 1993;Åkesson, 1994;Åkesson et al, 2001;Muheim et al, 2006;Engels et al, 2014;Chernetsov et al, 2017). However, sometimes songbirds tested in Emlen funnels show a preferred direction that does not coincide with their migratory goal (e.g.…”

Magnetic map in nonanadromous Atlantic salmon

“…As connectivity is lost or reestablished between freshwater habitats and the ocean, salmon appear immediately capable of employing a magnetic map for navigating a novel environment at a broad scale. The magnetic map we have demonstrated in nonanadromous Atlantic salmon may be further modified through natural selection acting on anadromous populations to be more robust or complex (e.g., to encode distance in addition to direction, or longitude in addition to latitude) (12,13,15). Moreover, it seems that the magnetic environment in which fish develop modulates this inherited map (18).…”

“…For instance, increasing evidence shows that long-distance migrants use Earth's magnetic field as a kind of "magnetic map" (Fig. 1) to assess their location along the migratory route and orient accordingly (7,(10)(11)(12)(13)(14)(15)(16)(17)(18). The strength and direction of the geomagnetic field vary predictably across the globe (Fig.…”

Geomagnetic field intensity as a cue for the regulation of insect migration

“…Organisms on the earth are generally surrounded in the geomagnetic field (GMF) all the time. Many animals have evolved the ability to sense or even utilize the GMF components of field intensity, direction, or both, although the details of the biophysical mechanisms are still largely unknown [1, 2]. Two mechanisms, including magnetite-based magnetoreception and radical-pair-based magnetoreception, have been mostly focused on for terrestrial animals [3-5].…”