Orientation of Birds in Total Darkness

Abstract

Magnetic compass orientation of migratory birds is known to be light dependent, and radical-pair processes have been identified as the underlying mechanism. Here we report for the first time results of tests with European robins, Erithacus rubecula, in total darkness and, as a control, under 565 nm green light. Under green light, the robins oriented in their normal migratory direction, with southerly headings in autumn and northerly headings in spring. By contrast, in darkness they significantly preferred westerly directions in spring as well as autumn. This failure to show the normal seasonal change characterizes the orientation in total darkness as a "fixed direction" response. Tests in magnetic fields with the vertical or the horizontal component inverted showed that the preferred direction depended on the magnetic field but did not involve the avian inclination compass. A high-frequency field of 1.315 MHz did not affect the behavior, whereas local anesthesia of the upper beak resulted in disorientation. The behavior in darkness is thus fundamentally different from normal compass orientation and relies on another source of magnetic information: It does not involve the radical-pair mechanism but rather originates in the iron-containing receptors in the upper beak.

Directional orientation of birds by the magnetic field under different light conditions

“…This also proved true for the fixed-direction responses in total darkness, under dim red and higher intensity turquoise light in robins Stapput et al 2008) and under bright green light and UV light in silvereyes . The fixed-direction responses are thus not controlled by the inclination compass.…”

“…This clearly demonstrates that the respective magnetic information is mediated by the iron-based receptors located there (Wiltschko, R. et al 2007bStapput et al 2008). with the inclination compass under white light and under dim monochromatic light from the short-wavelength part of the spectrum and (ii) fixeddirection responses in total darkness, under bright monochromatic light and bichromatic light.…”

“…The respective tests were performed under green and turquoise light (Ritz et al 2004;Thalau et al 2005;Wiltschko, R. et al 2005); it can be assumed, however, that tests under UV and blue light would produce the same results, because the responses under these conditions have the same general characteristics. Temporarily deactivating the magnetite-based receptors in the upper beak with a local anaesthetic, in contrast, did not have any effect under green light: European robins as well as Australian silvereyes continued to head into their migratory direction as before (Wiltschko, R. et al 2007aStapput et al 2008; see figure 7 below). The same was true for compass orientation in chickens ).…”

Low-frequency pulsed electromagnetic field exposure can alter neuroprocessing in humans

“…Hence the hypothesis that the effect is produced by induced currents is supported and suggests that the induction of analgesia, at least in humans, may depend on a different mechanism from that for animal orientation and homing. This is not surprising given current evidence that magnetoreception even in birds may be achieved by more than one mechanism with one dependent on light exposure (free radical mechanism) and one independent of light exposure (magnetite; Johnsen & Lohmann 2008;Stapput et al 2008). Even within the induced current paradigm, different pulse designs may differentially influence behaviour (Thomas et al 1997).…”

High levels of maternally transferred mercury disrupt magnetic responses of snapping turtle hatchlings (Chelydra serpentina)

“…While most studies have focused on the use of magnetic cues for goal-oriented movements, many animals also show spontaneous magnetic alignment (SMA) in which they align their body axis with respect to the Earth's magnetic field (e.g., cattle (Begall et al, 2008), foxes ( Cervený et al, 2011), dogs (Hart et al, 2013), songbirds (Stapput et al, 2008), salamanders and trout (Chew and Brown, 1989)). Although the mechanisms underlying SMA, as well as those underlying other magnetic responses, are still under debate, there are two leading hypotheses: 1) a magnetitebased mechanism (MBM), involving single domain or superparamagnetic particles of magnetite (Kirschvink et al, 2001) and 2) a radical pair mechanism (RPM) in which the Earth's magnetic field influences the spin states of unpaired electrons in specialized photopigment molecules, potentially altering the response to light (Maeda et al, 2008).…”