A Cold and Foggy Summer

A Mourning Dove coos its mournful song on this yet-another gray morning. The fog holds the hill in its embrace, hiding the dove and most everything else. The fog this morning in mid-August was wet enough to leave .02 inches in the rain gauge. With moisture dripping in heavy drops from the trees and with the temperature still in the low 50s, it feels convincingly like winter.

LHS in the Fog

According to Harold Gilliam in his excellent “Weather of the San Francisco Bay Region”, part of the California Natural History Guides published by UC Press, the wetness or dryness of the fog reflects where the fog originates. Wet fog is formed some distance at sea as part of a deep fog bank. By the time the wind has carried the fog to the coast, ample time has passed for droplets to have formed. Another weather source says that salt crystals are the nuclei around which droplets coalesce. Dry fogs are formed closer, often where fog first condenses over the hills.

This morning’s fog carries messages from out over the ocean where weather conditions this year have conspired to create a strong upwelling of cold water. Phytoplankton has flourished supporting an abundant crop of krill, a small shrimp-like crustacean which has attracted baleen whales to both Monterey Bay and the region around our Farallon Islands. Blue whales, as big as submerged islets, dive deep, filtering out the krill in their vast maws, while feeding Humpbacks make spectacular leaps into the air.

An imaginary sojourn out to sea among whales, orcas, and the sea birds helps relieve the silent tedium of so much fog on the hill. Or better yet are visions of the Sierra with sun-drenched forests of fragrant pine.

Most days the fog will yield to the sun around noon and we will have a few hours of cool sunshine before the fog bank rolls back in before sunset.

With a cold and wet May and a July which achieved a local record for having the coldest days, August appears to be no better. California is a national anomaly this year with even the interior valleys staying relatively cool, while the rest of the country bakes in humid heat.

The persistent fog is abetted by an entrenched area of low pressure which has the entire Pacific Coast in its damp grip. But even the low pressure trough will eventually yield to building high pressure, and sunnier, warmer days will surely return.

Even if this were a more ‘normal’ year with periods of fog alternating with sunny days, late July and August are quiet months in the bird year. With breeding season mostly past, there is no longer reason for song to defend territory or to attract a mate. It’s the season to pay attention to calls, which are part of the language of birds and contain even more complex variations than songs themselves.

By the middle of August most of the spring visitors who make up part of the local breeding population have headed south for the winter. In the interval between their departure and the arrival of the wintering birds, our year-round residents make up most of the bird population. In a temperate climate like coastal California, they are the single largest group.

But even in the slowest months, there’s always a possibility for surprise. Some years back, on such a foggy morning, a Rose-breasted Grosbeak visited my sunflower feeder.

Rose-breasted Grosbeak

I remembered seeing the bird in one of my bird books. Once seen, it’s impossible to forget—the strong black and white coloring with the vivid splash of red on its breast above a pure white belly. And to have seen such an exotic creature briefly on a foggy morning in the Berkeley Hills, gave the impression of having seen an apparition.

No such visual jolts this morning where at noon the fog has finally lifted enough to reveal one disheveled molting California Towhee scratching up seed from the saucer feeder.

Cast Offs —The Annual Molt

Discarded feathers are everywhere these days—stark black feathers with white vanes from crows and ravens, black and white tail feathers from Dark-eyed Juncos, blue-black ones from Steller’s Jays. Others are pale gray without markings. Some of the feathers have a tuft of down at their base which provides insulation and body warmth.

Molting is an annual event which is triggered by hormonal changes in response to the shortening days. Molting follows the breeding season—the time when the greatest demands are placed on a bird’s energies. Once breeding is over, every old feather is replaced by a new one. Molting also requires energy as each feather needs an initial infusion of blood to produce the protein in a new feather. During molting, birds are less active and mostly silent. Most birds molt before migration. But those species with long migrations will molt after their arrival in their wintering grounds.

Feathers are discarded in a symmetrical sequence so a bird is never without feathers for flight and for warmth. For songbirds, a complete molt takes several weeks. For certain species such a pelicans, geese and ducks—birds which tend to be heavy relative to their wing surfaces—loosing even a few flight feathers would compromise their flying ability. All the flight features are therefore shed at once and replaced, often within two weeks. Flightless for a time, the birds retreat to secluded lakes and rivers where they continue to feed.

In addition to the one complete molt a year in late summer, certain species such as buntings, tanagers, and warblers have a partial pre-nuptial molt in the spring where they acquire the colorful breeding plumage.

A very few species have two complete molts a year. They are the ones like our Marsh Wren who move through abrasive vegetation which causes feathers to wear prematurely.

Though song birds are in their seasonal eclipse associated with their molt, a new season has begun along the Bay shore with the return of shorebirds, some of whom nested as far north as the Arctic Circle. Often they arrive still in breeding plumage. The newly-arrived Black-bellied Plovers are resplendent in black and white which will soon be transformed to the drab grays and browns of winter.

Shorebird numbers will continue to increase with new arrivals daily.

And next month, in September, our wintering song birds will begin to show up—Ruby-crowned Kinglets, Golden-crowned Sparrows, Yellow-rumped Warblers—once again enlivening the local avian scene.

-- Phila Rogers

Phila Rogers is a Lawrence Hall of Science neighbor who has lived on the hill for 58 years. Until retiring, she was a science writer at Lawrence Berkeley National Laboratory where she also wrote “Nature Note” for the weekly publication. As a volunteer with the UC Botanical Garden she co-leads quarterly bird walks. She is also one of the founding members of Save Strawberry Canyon.

The attached bird photos are by Bob Lewis.