Abstract
Previously it has been shown that migratory birds were oriented in the appropriate migratory direction under UV, blue and green monochromatic lights (short-wavelength) and were unable to use their magnetic compass in total darkness and under yellow and red light (long-wavelength). Currently, it is generally assumed that the magnetic compass of birds works correctly only under short-wavelength light. However, it also been suggested that the magnetic compass has two sensitivity peaks: in the short and long wavelengths, but with different intensities. In this project, we aimed to study the orientation of long-distance migrants, pied flycatchers (Ficedula hypoleuca), in different monochromatic lights during autumn migration. The birds were tested in the natural magnetic field (NMF) and 120° CCW shifted magnetic field (CMF) under green and yellow light (intensity 1 mW m−2). All tests were performed in a specially constructed wooden laboratory equipped with magnetic coils to manipulate the magnetic field. We showed that (1) pied flycatchers were completely disoriented under green light both in the NMF and CMF but (2) showed the migratory direction in NMF and the appropriate response to CMF under yellow light. Our data contradict results of previous experiments under monochromatic yellow light and might indicate the previously proposed hypothesis of two different mechanisms in avian magnetoreception (a high-sensitive short-wavelength mechanism and a low-sensitive mechanism in the long-wavelength spectrum) has a right to exist.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Abstract updated: one sentence was rewritten (see new version below). Our data contradict results of previous experiments under monochromatic yellow light and might indicate the previously proposed hypothesis of two different mechanisms in avian magnetoreception (a high-sensitive short-wavelength mechanism and a low-sensitive mechanism in the long-wavelength spectrum) has a right to exist. Results updated: we added results of experiments in darkness (see details below). Under darknes condition in 2022, the birds showed northestern direction (α = 39 deg, n = 10, r = 0.61, p = 0.02, Figure 1C) which does not correspond with autumn migratory direction typical for this species. Discussion updated: two sentences were rewritten (see new version below). 1) UV/V cones are the only cone type with transparent oil droplets (intracellular structures that usually play a role of spectral filters and cut off short-wavelength light)... 2) Avian LWS and double cones contain the oil droplets that cut off wavelengths below about 570 nm and 450 nm, respectively [94,98]. This light is required for cryptochrome photoreduction, thus Cry4 could play a role of a yellow-light sensor in the long-wavelength mechanism of avian magnetoreception. Main text updated (Materials and Methods, Results, Discussion): total darkness was changed to darkness
