For the 35th year in a row, the Welcome Back Monarchs Day celebration drew visitors from all around to Natural Bridges State Park for the beginning of the Monarch migration in Santa Cruz.

“We come every time. I’ve been coming here since I was a kid,” said local Mercedes Ketterman on Sunday afternoon. “There were a lot more when I was a kid.”

Monarchs from east of the Rocky Mountains tend to migrate all the way down to central Mexico for the winter, and west of the Rockies they settle in southern California, many in Santa Cruz; but in recent decades the Monarch population has declined drastically. Habitat reduction and herbicides have reduced the main food source for the butterflies: milkweed.

Milkweed carries a natural defensive toxin that is imparted to the monarchs when eaten and it is necessary for the monarch larvae; but too much milkweed in a southern migratory region could be bad for the population as well. If the butterflies have an abundant food source in Santa Cruz, they might stay in the spring and fall victim to their natural predators.

“We can make a difference in what we do and what we allow to happen and changes we are involved with,” said Natural Bridges interpretive ranger Martha Nitzberg. “With this celebration, we are bringing awareness and empowering people to make changes.”

Children flapped around in cardboard wings made at art stations and a band played celebratory music to welcome the monarchs, but most of the day’s action was beneath the trees of the butterfly boardwalk. Sitting still on the branches these clusters of butterflies were nearly invisible. Once warmed by the sun, however, they would erupt in bursts of flight, accompanied by the awe of onlookers.