Oriented migratory flight at night: Consequences of nighttime light pollution for monarch butterflies

A behavioral assay to test sensory-cue-guided oriented flight in monarch butterflies under controlled conditions

“…Monitoring the temperature takes 1 min for each measurement. Note: Although the shop light that we use can increase the temperature around the flight simulator during testing, we found no negative effects of our light source on the monarchs that we tested in any of our previous work 1 , 11 and the heat emitted from the light did not affect the airflow around the flight simulator. Note: If you wish to specifically control or to directly test the effects of heat on monarch flight behavior in indoor flight simulator trials, you might consider using appropriate LED lights.…”

“…Animal interactions, such as fighting or mating, can occur while housed in the communal cage, which can affect the status of animals prior to their testing in trials. Note: Although animals are constrained in glassine envelopes, our own previous work 1 , 2 and those of other researchers 3 , 4 have found no negative effect on monarch behavior. Housing and storing butterflies in glassine envelopes during experimental studies involving monarch behavior has been a common and long-standing practice in the literature, 5 , 6 with some researchers using glassine envelopes since the late 1970s.…”

“… Position the flight simulator within the room such that no landmarks are visible to the butterfly when in the flight simulator during trials. Using a compass, position the flight simulator ( Figure 2 1 ) in the room such that north in the flight simulator (i.e., the position of the butterfly at the beginning of a trial) is aligned with geomagnetic north during trials.

Figure 2 Flight simulator apparatus used for testing the flight behavior of butterflies We use a flight simulator based on the original design by Mouritsen and Frost 9 that has been modified according to Reppert et al.

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“… Note: For this experiment, we use a light source that produces a photon flux intensity of 7.45 × 10 15 photons s -1 cm -2 which although is orders of magnitude less bright than the sun is sufficiently bright enough to elicit normal flight behavior in monarchs when it is the only source of light during trials. 1 , 11 Although we use a full-spectrum light in this study, full-spectrum light is not necessary to examine monarch flight behavior, as monarchs will fly normally even when exposed to non-full-spectrum light during trials. Non-full-spectrum light sources or the use of specialized light wavelength filters can test the role of specific wavelengths on oriented flight and the use of various compass mechanisms.…”

Lack of evidence for a fine‐scale magnetic map sense for fall migratory Eastern North American monarch butterflies (Danaus plexippus)

“…Evidence supporting this is that the overwintering sites in Mexico and California share similar temperature conditions during the period in which monarchs overwinter (Guerra & Reppert, 2013 ), whereas these sites are significantly different in geomagnetic field parameters, tree species used for overwintering (e.g., oyamel fir forests in Mexico and Eucalyptus trees, Monterey pines, and Monterey cypresses in California), environmental conditions (e.g., high altitude mountainous forests in Mexico and areas close to sea level in California), and level of human activity (e.g., urbanized versus rural areas). Once fall migratory monarchs reach these key microclimates, regardless of whether they are in Mexico or California, such temperature conditions, potentially in conjunction with other environmental cues that coincide with their arrival in these conditions (e.g., the loss or the lack of a specific solar angle that triggers southward directional flight in fall migrants; Parlin et al, 2022 ), might then trigger other aspects of the migratory biology of monarchs that then keep them there for the entire overwintering period. That fall monarchs have not been observed significantly south of the overwintering sites during the overwintering period supports this possibility.…”