| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
|
|
|
|
|
Naturalist's Almanac What to look for this Winter January Darting into the San Francisco Bay under the Golden Gate Bridge each winter are phenomenal runs of spawning Pacific herring. Adults congregate outside the Bay until increasing plankton levels signal that abundant food will be available for their future hatchlings. Then the slender, silver fish, which can grow up to 18 inches long, enter the Bay in droves to mate and lay eggs. Females deposit as many as 134,000 sticky eggs on eelgrass, kelp, or other fixed submerged objects. Larvae hatch about ten days later and gather in shoreline schools inside the Bay. The sudden abundance of delicious fish and succulent eggs is noticed by hungry predators, making this a peak time to spot marine mammals such as California sea lions in the area. Predatory fish and seabirds also join the feeding frenzy. As if that weren’t enough, there is a significant commercial harvest centered around herring eggs; $16 million worth of roe is exported to Japan each year. With the next generation still wallowing in larval form in the slippery muck of icy cold ponds, and most adults having died in the previous autumn’s chill, it’s something of a shock to encounter dragonflies in the midst of winter. But believe it when you see it, because sharp-eyed naturalists are reporting a surprising variety of dragonflies and damselflies on dates once considered too early for these chimerical insects (www.sonic.net/dragonfly). One especially hardy species, the variegated meadowhawk, appears so persistently that it may even overwinter in adult form. Adorned with olive, gray, and red plaid markings on their bodies, and orange veins in their wings, meadowhawks are striking and vivid to the eye when freshly emerged. Wear and tear makes older insects dull and bedraggled. Look closely at all winter dragonflies to help solve the riddle of whether some adults overwinter or simply hatch early from larvae on warm winter days.
In winter 1999, Philip Unitt of the San Diego Natural History Museum followed up on a brilliant hypothesis that explained why the poorly known gray vireo might winter in California. In parts of northern Mexico, these diminutive birds are associated with elephant trees, rare desert trees named for their short, stout trunks and branches. Unitt wondered if the birds would overwinter in similar stands at Anza-Borrego Desert State Park’s Alma Wash. A series of subsequent surveys discovered vireos, the first wintering population ever detected in California, feeding heavily on elephant tree fruits. With vireo numbers declining and elephant trees already considered endangered in the state, this tiny pocket of life needs to be carefully encouraged if it is to maintain its precarious hold. FebruaryAlthough it is not something you’re likely to witness, this is breeding season for our largest rodent, the beaver. Leading mostly aquatic, nocturnal lives, beaver are rarely observed except during a narrow window at dusk as they begin the evening’s activities and there’s still enough light to see them. Beaver are better known by the signs they leave behind—not only chewed trees and stick lodges that sometimes block rivers, but also “beaver pies” stacked around the perimeter of a territory. These are piles of mud and leaves up to two feet high made by members of a family group and marked with castoreum, a sweet smelling musk released from anal scent glands that serves as a social signal between beavers. Three months after mating, two to four kits are born within the parents’ lodge and begin walking, swimming, and playing almost immediately. Think of the dark, dreary, rain-dripping depths of a forest and you’re not likely to imagine winter-blooming flowers. Yet this is one surprise awaiting anyone willing to venture into the woods of California’s north coast. The five- to ten-foot-high Indian plum shrub, for example, leaps out like a green flame in the drab winter gloom, sporting clusters of dangling white flowers and erect tufts of new, brilliant green leaves. At the same time, sprays of red-flowering currants and carpets of bright-faced trilliums add color to the scene. Observers who take the time to look closely will find more subtle displays of fetid adder’s-tongue lily, redwood sorrel, miner’s lettuce, and wild ginger. Redwood National Park and the adjacent state parks are ideal settings for viewing these and many other early flowers.March Like an ancient giant rousing from winter slumber, Mono Lake awakens with the exuberant abundance for which it is famous. Trillions upon trillions of the lake’s endemic brine shrimp hatch from cysts (sporelike eggs) that have spent the winter dormant in the cold depths. Larval shrimp, or nauplii, swarm to the surface and begin devouring the algae that colors the lake’s waters a murky pea-green all winter long. So abundant and voracious are the shrimp, that by June underwater visibility increases tenfold. Then in late summer, the shrimp cast their eggs into the lake’s depths before dying in the increasingly chilly water. Many are eaten by the nearly two million eared grebes that descend on the lake during their migration south. As soon as the shrimp disappear, algae begin a dramatic resurgence throughout the following winter. Old legends may die hard, but there is still a nugget of truth to the story that swallows return to San Juan Capistrano each year on March 19, St. Joseph’s Day. It’s a hope strong enough to draw some 12,000 tourists on that day, and even more people for the weekend Swallows Festival, the most popular tourist destination in Orange County after Disneyland and Knott’s Berry Farm. Fact is, over the course of several days, large numbers of cliff swallows do return each spring to the Mission founded in 1776 by Father Junipero Serra. The experience beats visiting an amusement park. Watching the real thing has its own brand of magic.
David Lukas leads natural history tours and programs in the Bay Area. He can be reached at davidlukas@earthlink.net |