Text and research by the California Center for Natural History
Migration
Every fall more than 250 species of birds migrate through the Bay Area, and among them are at least 19 species of raptors. Tens of thousands of individual birds of prey ride the region’s strong winds, migrating through the Golden Gate toward their wintering grounds where they’ll rest, eat, and escape the cold. The Golden Gate Raptor Observatory’s Allen Fish estimates that as many as 12,000 of those birds, or almost a third of the fall raptor sightings, are red-tailed hawks (Buteo jamaicensis); they’re the raptors that most commonly migrate through the area, with turkey vultures a close second. These thousands come in two waves—juveniles dispersing to Northern and Central California peak around late September, and juveniles migrating to Central and Southern California peak in mid-November. Look for red-tails over westward-facing grassy hills, like Windy Hill Open Space Preserve, Hayward Shoreline, Carquinez Strait, and outer Point Reyes.
Sea sparkle
When Noctiluca scintillans, one of the many species of bioluminescing dinoflagellates responsible for glowing surf in the region, appear in autumn, it’s one sign that California’s famous cold-water, food-rich upwelling off the coast has come to its seasonal end. The tiny protists light up when jostled, likely in order to deter would-be predators; the flash either startles predators or exposes them, attracting an even larger predator to eat the offender. Though in the water year-round, Noctiluca concentrations are highest as northwesterly winds settle, upwelling slows, waters smooth, and the protists swim to the top of the water column, becoming more visible.
Jack O’Lantern
The orange mushrooms growing from decaying wood in late fall are likely western jack o’lanterns (Omphalotus olivascens). Though toxic to eat, a fresh, mature specimen is a feast for the eyes: At night, look for a neon-green glow around the gills. The bioluminescence may help the mushroom reproduce by attracting nocturnal insects to transport and spread its spores.
Autumn color
Brilliant reds can carpet the edge of the Bay where the brackish tide sweeps in and out daily and stubby pickleweed (Salicornia ssp.) grows. The native succulent accumulates salt in the green-gray tips of its jointed segments, which, saturated with salt by autumn, turn red and break off. Also, pink and red poison oak leaves (Toxicodendron diversilobum) color the forests before dropping for winter.
Navigational web
Fall is spider season—many species are at their largest and courting, mating, or producing egg sacs. Orb weavers build large, wheel-shaped webs seemingly everywhere in the Bay Area, and one species, the banded garden spider (Argiope trifasciata), does a cool trick: Its web can double as a compass. The spider weaves its round web on an east-west axis and rests in the center with its black abdomen facing south toward the sun’s warming rays. Spiders get cold, too.
Nightlight
To glimpse a bobcat (Lynx rufus), wait for a new moon in the fall and then head out during the day. Even though bobcat prey—often small rodents—are more active during the dark cover of a new moon, bobcats, unlike most cats, can’t see well in the dark, so they shift to daylight hunts during the fall’s cool days, saving night hunts for crescent or quarter moons.
