Lack of evidence for a fine scale magnetic map sense for fall migratory
Eastern North American monarch butterflies (Danaus plexippus)
Abstract
How first-time animal migrants find specific destinations remains an
intriguing ecological question. Migratory marine species use geomagnetic
map cues acquired as juveniles to aide long-distance migration, but less
is known for long-distance migrants in other taxa. We test the
hypothesis that naïve Eastern North American fall migratory monarch
butterflies (Danaus plexippus), a species that possesses a magnetic
sense, locate their overwintering sites in Central Mexico using
inherited geomagnetic map cues. We examined whether overwintering
locations and the abundance of monarchs changed with the natural shift
of Earth’s magnetic field from 2004 to 2018. We found that migratory
monarchs continued to overwinter at established sites in similar
abundance despite significant shifts in the geomagnetic field, which is
inconsistent with monarchs using fine scale geomagnetic map cues to find
overwintering sites. It is more likely that monarchs use geomagnetic
cues to assess migratory direction rather than location and use other
cues to locate overwintering sites.