Do monarch butterflies use polarized skylight for migratory orientation?

Abstract

SUMMARY To test if migratory monarch butterflies use polarized light patterns as part of their time-compensated sun compass, we recorded their virtual flight paths in a flight simulator while the butterflies were exposed to patches of naturally polarized blue sky, artificial polarizers or a sunny sky. In addition, we tested butterflies with and without the polarized light detectors of their compound eye being occluded. The monarchs' orientation responses suggested that the butterflies did not use the polarized light patterns as a compass cue, nor did they exhibit a specific alignment response towards the axis of polarized light. When given direct view of the sun, migratory monarchs with their polarized light detectors painted out were still able to use their time-compensated compass: non-clockshifted butterflies, with their dorsal rim area occluded, oriented in their typical south–southwesterly migratory direction. Furthermore, they shifted their flight course clockwise by the predicted ∼90° after being advance clockshifted 6 h. We conclude that in migratory monarch butterflies, polarized light cues are not necessary for a time-compensated celestial compass to work and that the azimuthal position of the sun disc and/or the associated light-intensity and spectral gradients seem to be the migrants' major compass cue.

An experimental displacement and over 50 years of tag-recoveries show that monarch butterflies are not true navigators

“…4). This result may appear surprising because vector navigation is the simplest conceivable strategy leading to the least concentrated distribution given the monarchs' known compass orientation capabilities (23,24,26). What we may see here are the effects of additional complicating factors.…”

“…Both vector navigation (21) and true navigation (22) have been suggested as strategies used by monarchs to find their overwintering sites. To examine these competing hypotheses, we displaced monarchs from Ontario to Alberta provinces in Canada during fall migration and used flight simulators (23,24) to track their migratory direction. We also used over 5 decades of tagging-recovery data to estimate the directional concentration of monarch butterflies during fall migration, and then compared these results with two mathematical models describing the directional distribution of migrants expected under a simple vector-navigation strategy (16,25).…”

Diurnal dung beetles use the intensity gradient and the polarization pattern of the sky for orientation

“…This agrees with conclusions drawn from other experiments (Byrne et al, 2003;Dacke et al, 2014) and further supports the idea that the sun is the most important cue for the orientation system of diurnal dung beetles. This conclusion also holds true for monarch butterflies (Reppert et al, 2004), where polarized skylight seems to play only a minor role as a compass cue (Stalleicken et al, 2005). In contrast to this, ants and crepuscular beetles, primarily, rely on polarized light for orientation (Dacke et al, 2004;Wehner and Müller, 2006).…”

Light habitats and the role of polarized iridescence in the sensory ecology of neotropical nymphalid butterflies (Lepidoptera: Nymphalidae)

“…Ultraviolet pattern elements in butterflies are often structural in nature and therefore might also be polarized (Silberglied, 1984;Kemp et al, 2005). Furthermore, recent work on the nymphalid butterfly Danaus plexippus has shown that the dorsal rim area of their compound eyes is sensitive to ultraviolet polarized light and that this may function in skylight orientation (Sauman et al, 2005;Stalleicken et al, 2005). Due to limitations inherent in the methods of this study, the potential importance of ultraviolet polarized patterns on butterfly wings could not be assessed.…”