Plight of the butterflies
Reign of the monarchs is in decline, but no one knows reason for the drop in population By Zeke Barlow Thursday, January 3, 2008
The Ellwood Main Monarch Butterfly Grove in Goleta is one of the largest monarch sites in the U.S. The eucalyptus trees provide shelter for the butterflies so they can survive the winter.
This is the time of year when thousands of monarch butterflies are hanging from eucalyptus limbs while hunkering down for the winter.
The annual spectacle of orange and black clusters clinging to trees draws people from all over the state. But not this year.
Butterfly populations along the coast are the lowest anyone has seen in years, which follows the trend of a population that has been declining for more than a decade. Those who track the butterflies wonder if this is part of a larger problem — such as drought or parasites — or just a statistical dip in the population that naturally vacillates.
Mia Monroe, with the Xerces Society California Monarch Campaign, said the low numbers could be a natural blip. But for those who love monarchs, “it’s a concern.”
In the core area where the monarchs winter, from Santa Cruz to Santa Barbara counties, numbers are down as much as 80 percent, Monroe said. In Pacific Grove, one of the most popular places to watch their wintering habits, only 10,000 butterflies have been counted, compared to more normal counts of 50,000 to 70,000. At two popular spots in Ventura, it was hard to spot any of the monarchs that normally winter there. The theories as to what is causing the decline varies.
Jessica Griffiths, a wildlife biologist and amateur lepidopterist (butterfly scientist) with the Ventana Wildlife Society, said she suspects this year’s dry conditions may be to blame for the low numbers. But entomologist Paul Cherubini said he thinks the decline is not because of the dry spell, but because of an exotic parasite eating the eggs in the butterfly breeding grounds.
The annual cycle of the tiny creatures starts in the Central Valley, where adults lay as many as 400 eggs on milkweed plants. Those eggs morph into caterpillars that eat the milkweed and eventually become butterflies that soon start another generation.
After three or four generations during the spring and summer, the butterflies head to the coast when the days start to grow shorter, where warmer temperatures provide a wintering ground.
The exact mechanics of how they know where to migrate are a bit of a mystery, which only adds to their allure.
This cycle seems to have been interrupted at the beginning, when eggs are laid in the milkweed. Griffiths suspects that dry conditions have led to less milkweed, thus fewer eggs. Cherubini thinks some exotic predator is eating the eggs before they are able to morph into caterpillars.
One year of low eggs is not that much of a concern, Griffiths said. Populations vary greatly.
“We have to keep a level head and not panic because they are insect populations that can recover from population declines as long as the conditions that caused that decline don’t persist,” she said.
It’s what happens if there are multiple consecutive dry years that can be a problem. Many are predicting this year to be another dry one.
“That could be bad news for them,” she said. “Sustained drought could be a problem.”
But Cherubini thinks a trend of a shrinking population is well under way.
“As far as having to deal with the reality that the population is lowering in the coming decades, that’s a genuine concern,” he said.
What makes things even worse is the butterflies’ shrinking habitat. With more farming in the Central Valley, there is less land with milkweed on it. And when eucalyptus trees are cut down along the coast, it also reduces habitat for butterflies.
Monroe is encouraging people to plant milkweed, not burn fires near clusters of butterflies on branches and refrain from cutting down eucalyptus, pine or redwood trees where butterflies rest for the winter.
Cherubini said research into the decline is virtually nonexistent, partly because it would be such a challenge. Monroe can’t imagine a world without the monarchs. She loves them not only for their beauty but also for their resilience in migrating long distances.
“They are a way we can appreciate the beauty and wonder of nature,” she said.