Dwindling numbers of visiting monarch butterflies cause concern
For many years, monarch butterflies have been a seasonal attraction at Ardenwood Historic Farm in Fremont, where they spend the winter as part of their migratory, multigenerational life cycle.
Every year from November through January, monarch butterflies congregate in the park’s eucalyptus groves, their black and orange wings creating an autumn leaf effect in the trees.
Their stopover is part of what has been described as an intergenerational relay race, during which the monarchs spend parts of their life cycle in habitats ranging from the western slopes of the Rocky Mountains to the California coast.
In recent times, however, the monarchs’ population has been sparse at best, leading to concerns that the insects are on the way to extinction.
Kristen Van Dam, an East Bay Regional Park District ecologist, provided an update on the monarchs’ status at a recent meeting of a district Board of Directors subcommittee.
There are two populations of monarch butterflies in the United States, she said, separated by the Rockies. The western group ranges from Washington state to Mexico.
Monarchs have been seen spending the winter in four regional parks: Ardenwood, Point Pinole, Oyster Bay and Coyote Hills. By far the largest group is at Ardenwood; a few show up at Point Pinole. Although monarchs have been seen flying through all regional parks, they seem to roost only at the four just mentioned.
Scientists have noticed a 99% decline in the monarch population in the past 30 years, with the greatest decline in 2017 and 2018. There’s no single explanation. Factors include loss of habitat, use of insecticides, disease, predation, climate change and fires.
The monarchs leave the overwintering sites to breed inland on milkweeds. The caterpillars feed exclusively on milkweed; adults can use other nectar sources too.
In terms of habitat, overwintering monarchs need good places to roost (eucalyptus at Ardenwood and Point Pinole), protection from the wind and enough sunlight to keep warm.
The park district’s role in monarch preservation has been maintaining the overwintering and breeding sites, expanding nectar planting, public education and collaborating with other public agencies and nonprofits such as the Xerces Society, which is dedicated to monarch butterfly protection.
Van Dam says the park district obtained a grant to fund removal of some trees at Point Pinole to enhance the overwintering habitat for monarchs and the district has planted some pollinator gardens for the butterflies.
There also are plans to create monarch-friendly habitat at Diablo Foothills Regional Park and
Black Diamond Mines Regional Preserve.
For the public, if you establish a monarchfriendly garden, monarch scientists strongly recommend that you plant native milkweed, not the tropical variety.
The naturalists at Ardenwood Historic Farm usually schedule a series of programs highlighting the overwintering monarch butterflies. Although Ardenwood is closed and all in-person naturalist programs are on hold because of the coronavirus pandemic, you can still learn about the beautiful monarchs.
Visit the Xerces Society website at xerces.org.
RdOPdNINkS >> Here’s some good news — the park district plans to reopen some of its facilities starting Oct. 2.
At Del Valle Regional Park south of Livermore, reopenings will include the boat launch, boat rentals, the family campground at reduced capacity, and day use on the lake’s east side at reduced capacity.
At Quarry Lakes in Fremont, the boat launch ramp will reopen. The family campground at Anthony Chabot Regional Park near Castro Valley will reopen at reduced capacity.
And the boat launch and marina concession at Lake Chabot reopened Sept. 10.
Because of the pandemic and fire season, circumstances are always changeable. Your best bet is to check the park district webpage at bayareane.ws/3hhHdvS for upto-date information.