When is the ideal time for an eastern monarch to migrate south?

In the eastern United States, monarch butterflies begin migrating south in late summer. Using tagging data collected through Monarch Watch, a long-term community science program, Taylor et al. (2019) found that monarch migration was most successful when monarchs followed a sun angle between 46.0° and 56.8° at noon. In the northern United States, monarchs that started migrating in early August to late September were most likely to reach the overwintering grounds. In the central and southern United States, migration was most successful was from early September to late October. To learn more, check out this new map: How does timing affect monarch fall migration success?