Monarch butterflies find winter refuge in East Bay Parks

CONTRA COSTA COUNTY—For many years, monarch butterflies have been a seasonal attraction at Ardenwood Historic Farm in Fremont. That is because 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 create an autumn leaf effect in the eucalyptus trees.

Their stopover is part of what has been described as an intergenerational relay race. The monarchs spend parts of their life cycle in habitats ranging from the western slopes of the Rockies to the California Coast.

Fighting extinction

In recent times, however, the monarchs’ population has been sparse at best. This raises 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 Park District Board of Directors subcommittee.

There are two populations of monarch butterflies in the United States, she said, separated by the Rocky Mountains. 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.

99 percent decline

Scientists have noticed a 99 percent decline in the monarch population in the last 30 years.  The greatest decline occurred 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). They also need 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, and public education. They also collaborate with other public agencies and nonprofits such as the Xerces Society. Xerces is dedicated to monarch butterfly protection.

Van Dam said that the park district obtained a grant to fund removal of some trees at Point Pinole. This will enhance the overwintering habitat for monarchs. And the district has planted some pollinator gardens for the butterflies.

Creating monarch-friendly habitat

There are also plans to create monarch-friendly habitat at Diablo Foothills Regional Park and Black Diamond Mines Regional Preserve.

For the general public, if you do establish a monarch-friendly garden, monarch scientists strongly recommend that you plant native milkweed, not the tropical variety.

The naturalists at Ardenwood Historic Farm usually schedule a whole series of programs highlighting the overwintering monarch butterflies. Although Ardenwood is closed and all in-person naturalist programs are on hold because of the ongoing coronavirus pandemic, you can still learn about the beautiful monarchs. Visit the Xerces Society website at www.xerces.org.

Park reopenings Oct. 2

Here’s some good news. The park district plans to reopen some of its closed facilities starting on Oct. 2.

• Del Valle Regional Park south of Livermore. Re-openings 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.
• Quarry Lakes in Fremont. The boat launch ramp will reopen.
• Anthony Chabot Regional Park. The family campground near Castro Valley will reopen at reduced capacity.
• The boat launch and marina concession at Lake Chabot reopened on Sept. 10.

Because of the pandemic and the fire season, circumstances are always changeable. So your best bet is always to check the park district website, www.ebparks.org for up-to-date information. Click on “COVID-19 & Wildfire-Related Closures” at the top of the home page.

Ned MacKay writes a regular column about East Bay Regional Park District sites and activities. Email him at nedmackay@comcast.net.