Each winter, monarch butterflies (Danaus plexippus) from the western U.S. and Canada migrate hundreds of miles to coastal California and Baja California, Mexico. They seek protection from freezing temperatures and winter storms, which they find in temperate forest groves along the Pacific coast.
In the East Bay, monarchs migrate to and spend the winter at four primary locations: Point Pinole Regional Shoreline (Richmond), Coyote Hills Regional Park (Fremont), Ardenwood Historic Farm (Fremont), and the Monarch Bay Golf Course in San Leandro.
Monarch populations fluctuate greatly; as many as 25,000 were counted at Ardenwood in 1997, with more modest numbers in recent years varying from two hundred to two thousand. This year the numbers look promising for Bay Area monarchs, although the official annual count won't be done until Thanksgiving weekend.
The butterflies will remain clustered in sheltered groves until longer days and warmer temperatures signal the time to begin mating. After mating, the male monarchs will expire and the fertilized females will disperse in search of milkweed onto which they will deposit their eggs.
According to Park District Resource Analyst Jessica Sheppard, the best time to view clustering monarchs is in the morning, before the ambient temperature reaches 55 degrees (Fahrenheit), or late in the afternoon. In the warmth of the midday sun, many of the butterflies leave the trees seeking flowers and water.
Guided monarch walks and programs for all ages are offered at Ardenwood Historic Farm on weekends, from late November through February 5th.
Richmond area visitors may seek out a clustering group of several hundred monarchs at Point Pinole Regional Shoreline. Their resting spot - high in the trees south of Biazi Trail - is marked with flagging tape on nearby trees.
For program information visit the East Bay Regional Park District's web site at www.ebparks.org or call 1 (888) 327-2757.