The Greater San Francisco Bay Climate

Spring   Birds migrating from more southerly latitudes begin showing up as early as mid January and extend through June. During this period  shorebirds, now in bright breeding plumages, fatten up in preparation for the long flight to their northern breeding grounds..Many of them remain in California through March or April before heading out. The forests reach the peak of activity in May and June with breeding displays and nest building activities of songbirds. Wildflower blooms peak in the valleys, coast side and desert about March/April, on into May and June in the foothills and higher elevations. In the coastal mountains black bears begin stirring out of their long winter nap around February/March hungry and foraging for food. Northbound California Gray Whales can occasionally be seen making their way back to the Bering Sea and Gulf of Alaska from Baja but are typically a little further off shore on this leg of their migration. Marine mammal colonies are still very active with the adults in the early stages of parenthood at this time.

Summer    Hyperactive Hummingbirds zip and dazzling butterflies flutter from bloom to bloom in search of nectar while Ospreys make spectacular dives for unsuspecting fish.   Swallows amass by the hundreds and sometimes thousands scooping up flying insects on and above lakes, ponds and meadows. Residents bird such as the Wrentit, Towhees, Vireos and Brown Creepers, along with a large variety of Woodpeckers are busy raising their fledglings in the coniferous and broad leaf forests. Southern seabirds such as Brown and American White Pelicans fly up from the south perhaps to enjoy the cooler weather or better fishing and mingle with gulls, Cormorants, Avocets, Stilts & Herons. The coastal areas cooled by marine influence provide a respite from the summer heat while the Sierra and Coastal mountain ranges offer spring like conditions in the higher altitudes.

Fall  The first signals of the fall migration actually happen in late summer as shorebirds begin trickling in to the coastline and estuaries in late July. This is the most exciting time of year for us as nearly 20 species of migrating raptors are funneled along the coast through the Marin Headlands using the thermals to gain elevation before crossing the open waters of the Golden Gate. During the peak of the hawk migration in late September sometimes hundreds of raptors can be witnessed in a single outing. At this same time of year the shrubs and trees become alive with migrant songbirds either in route to more southerly latitudes or setting up shop for the winter. Early fall rains can bring many unusual birds that will take shelter in woodland areas along the coasts and bays. This is also the best time of year for observing the rutting behavior of deer and elk. The California Gray Whales can be seen on their southbound migration starting in November while the Monarch Butterflies start showing up on land. Fall colors begin in September, peak in early October in the mountain areas, late October to early November at lower elevations.

Winter  Habitat and seasonality bring constant change to the diversity and abundance of species in the area. Winter has the greatest variety of birds as many fall migrants stay on to enjoy the moist, relatively warm winter and join the resident birds like the California Quail. Millions of ducks, geese and grebes descend from the north through the Pacific Flyway to over- winter in the Klamath and Mono Basins, Central Valley and San Francisco Bay estuaries. This is also the peak time to observe marine mammals as they re-establish historic rookeries along the Pacific coast. Depending on when the first heavy rains begin, Steelhead Trout, Chinook and Coho Salmon begin their epic trip to spawning grounds.   These fish can occasionally be seen in the coastal streams and rivers throughout Northern and Central California during this time of year.

Nature's Calendar - California