| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
|
|
|
Naturalist's Almanac What to Look for this Fall OctoberIn a season when California's native maples, cottonwoods, oaks, dogwoods, and aspens are staging a spectacular color show, leaves on alder trees remain green, even when they fall. This oddity is partly due to the trees ability to convert or "fix" atmospheric nitrogen into a usable form, a trait alders share with legumes (beans, clovers, etc.). Before falling, the leaves of most deciduous trees shunt hard-won nutrients back into branches and roots for winter storage. But with nitrogen to spare, alders are not so stingy, shedding leaves still laden with the nutrient. Pioneering alders draw on their nitrogen-fixing prowess when colonizing barren soils such as flood-scoured riverbanks and gravels deposited by receding glaciers. Traditional farmers value the tree. In the highlands of Guatemala, farmers mulch vegetables with alder leaves and spare the trees when clearing fields for crops. A study in Sikkim in the Himalayas found that cardamom bushes growing under alders produced over twice the yield of bushes grown beneath other trees. Most aquatic insects that live as larvae in California's rivers emerge as winged adults in spring through late summer. But the October caddisfly is an exception. On fall evenings in north state rivers such as the Pit and lower Sacramento, these inch-long insects with fuzzy wings and orange bodies pull themselves out of their pupal cases and fly into the air. The hatch elicits quite a stir among trout, which gorge themselves on egg-laying caddis that alight on the rivers surface to deposit egg masses on floating vegetation. (The event also causes a commotion among fly-fishing anglers, who use fly patterns that mimic the insects to catch furiously feeding fish.) If you cant get to a river during the hatch, look for caddis larvae in the summer. They're the creatures that walk along riverbeds encased in their tubular "shells" made of tiny bits of sand, gravel, leaves, and twigs all spun together with silk. NovemberCalifornia's 18 oak species ripen their acorns in the fall. Rich in oils and carbohydrates, these heavy seeds fuel a feeding frenzy among dozens of animals, from weevils to bears. Oaks get little in return from most acorn eaters, but squirrels and jays carry acorns away from the tree and store many of them in the ground, providing an indispensable seed-dispersal service. Squirrels are uncanny acorn connoisseurs. Eastern gray squirrels are known to cache healthy acorns and acorns high in tannins and fats, while often eating straightaway those infested with weevils or with lower tannin and fat content. Acorns of some oak species germinate in the fall, shifting about half their calories into tiny seedlings, which most animals find unpalatable. This is probably why some squirrels chew off the embryos of fall-sprouting acorns before caching them but store spring-sprouting acorns intact. Squirrels will also take more care with big acorns, carrying them further from the tree and burying them more deeply than smaller acorns. California gallflies (a misnomer, they're actually cynipid wasps) are one of those self-fertile species that gets along fine without males. Females a tad smaller than rice grains emerge from their galls in October and November and set to work laying eggs under the bark of twigs on California's "white oaks," which include valley, blue, and scrub oaks. When wasp larvae hatch in spring, they secrete a substance that causes their oak hosts to grow succulent green or red galls that reach the size of tennis balls in just two months. Bitter tannic acids in the lumpy spheres repel hungry predators, protecting larvae until they mature into adults and emerge after one or more years. As the gall ages, its surface turns hard and creamy white or tan. Its outer flesh grows pithy while an inner chamber that houses the larvae hardens. Galls can hang on the tree for a few years after wasps leave, harboring a host of other insects. A good place to find southern rain beetles, Pleocoma australis, (see page 40) is at Hurkey Creek Campground about eight miles from Idyllwild in the San Jacinto mountains. Male beetles dig their way out and take wing during the evening and at night for a week or two after the first soaking rain. Look for them around lit porches or streetlights (headlights will do, too), especially in damp weather. In central California Pleocoma blaisdelli can be found in Calaveras County near the towns of Arnold, Avery, and Sheep Ranch. Bay Area residents can search for Pleocoma behrensi in wooded areas (but not under eucalyptus) of the Berkeley Hills. DecemberBreeding season for most mule and black-tailed deer populations in California starts in November or December. Bucks signal their presence to one another by "horning," scraping antlers on bushes, branches, poles, or tree trunks. As often as every 50 to 200 paces, a buck will pause to horn, then lift his head to listen for a like response. Dozens of bushes and small trees with broken branches and flayed bark are left in the wake of a horning buck. For weeks in advance of breeding, unequally ranked bucks engage in courtly sparring matches that establish and reinforce social hierarchy. A dominant buck solicits a match by approaching a subordinate, head low, eyes averted, ears back or folded out, hair erect, and tail whipping side to side. Its the smaller animals choice whether to hook antlers to begin a ritualized neck-twisting contest that can last more than an hour. Dominance fights between mature, evenly matched males are much rarer. Brief and violent, they occur at the peak of rut, and can leave one or both animals with ugly wounds or gashes from antlers and hooves. Liese Greensfelder is a freelance writer living in Nevada County, California. |
Fall 2000
|
