Migratory birds are able to choose the appropriate migratory direction under dim yellow monochromatic light

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 lights (long-wavelength). Currently, it is generally assumed that the magnetic compass of birds works correctly only under short-wavelength light. However, at the same time, there is an assumption 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 (1) pied flycatchers were completely disoriented under green light both in the NMF and CMF and (2) for the first time they showed the migratory direction in NMF and appropriate response to CMF under yellow light. Our data suggest that the avian magnetic compass might be based on two different mechanisms: a high-sensitive short-wavelength mechanism and a low-sensitive mechanism in the long-wavelength spectrum.