Western Monarch Day

What the day is

Western Monarch Day is observed on February 5, in the middle of the overwintering season along the California coast, when the butterflies are clustered and countable.

Origin and background

North America has two monarch populations separated by the Rocky Mountains. The eastern one migrates to central Mexico and is the famous one. The western population winters in groves along the California coast, in eucalyptus, cypress and pine, hanging in dense clusters that keep them sheltered and just cool enough to conserve energy.

Their numbers are the story. Counts in the 1980s ran into the millions. By the winter of 2020 the annual volunteer count recorded fewer than two thousand butterflies across all known sites, a decline of well over ninety-nine percent, and it looked as though the population was going. Numbers then recovered into the hundreds of thousands over the following seasons, which nobody fully predicted and nobody has fully explained. A recovery from that base is fragile rather than reassuring.

The causes are the familiar combination: loss of breeding habitat and the milkweed monarch caterpillars depend on absolutely, pesticide use, climate pressure on both ends of the migration, and degradation of the specific groves they return to.

One piece of well-meant advice turns out to be harmful. Planting tropical milkweed, which stays green year-round in mild climates instead of dying back, can interrupt the migratory cycle and allows a parasite to build up on the plants. Native milkweed species, which senesce naturally, are what conservation groups now recommend.

The count itself is done by volunteers, which makes this a rare case where an ordinary person can contribute directly to the primary dataset.

How to take part

• Visit an overwintering grove and stay on the paths. Disturbed clusters burn energy they cannot spare.
• Plant native milkweed, not tropical, and check which species belongs where you live.
• Plant nectar flowers that bloom late, which fuel the journey.
• Volunteer for the Thanksgiving or New Year count.
• Stop using broad-spectrum insecticide in the garden.