How fast does the migration advance?
In the midwest, we have observed that 5-6 days after masses of Monarchs assemble in Minneapolis/St. Paul (late August) the front of the migration reaches Des Moines, Iowa (4-6 Sept.) – a distance of 240 miles (360 km). It takes another 5-6 days for this wave, or front, to reach Lawrence, Kansas (usually 9-10 Sept.) – another 220 miles (330 km). However, from Lawrence, KS to Austin, TX a distance of 700 miles (1050 km), the interval varies from 6-14 days. The first masses of Monarchs usually reach the Texas/Mexico border (Eagle Pass, etc.) in the last days of September. In the midwest, if we assume the migration starts in NW Minnesota, the distance to the border is 1500 miles (2250 km). Therefore, the migration advances at roughly 50 miles (75 km) per day (1500/30 migrating days from 28 Aug. to 28 Sept.). However, these are averages, and there are reports from recoveries of tagged Monarchs which indicate flight distances up to 129 km a day.
