Final Days, First Miles

The overwintering season is coming to an end. Northbound butterflies are flying from their winter sanctuaries and early arrivals are being reported from the migration trail.

Monarch Butterfly departing from Sanctuary in Mexico — The first mile of the journey north. Near El Rosario Sanctuary, March 11, 2018 by Estela Romero.

Witnessing Departure

One after another, monarchs flew downhill away from El Rosario Sanctuary and headed north. Estela stood as a silent witness as northbound butterflies began the first mile of their journey north.

That was Sunday, March 11. On Monday, she received news of a mass departure from Sierra Chincua:

"The butterflies vacated the sanctuary today, sometime during a two-hour window. The guides saw the butterflies at noon and, when they came back at 2 pm the monarchs were suddenly gone!" reports Estela. More...

Many Monarchs Remain

No mass departure has been reported from El Rosario, and movement out of Cerro Pelon has been gradual. Ellen Sharp reports:

"The long, staggered arrival we witnessed last fall (when they arrived on October 27 and continued to arrive well into December), seems to be mirrored by a long, staggered departure. Their numbers are decidedly depleted, but for the moment they are still with us." More

Time to Go!

Full departure from the sanctuaries always occurs by the end of March. Sometimes it's sudden and dramatic and other times it's almost imperceptible. But time is running out and the butterflies must leave. The monarchs are in a race against time. They can't stay in Mexico any longer — but they can't move north too quickly either. The timing of the monarchs' spring migration must be precise. How do they know when to leave, and why do they go now?