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Notes on Winter and Early Spring Bird Activity on the Farallon Islands, California

Asa C. Thoresen
Publication Information
5 (September-October)
From Field and Study

Notes on Winter and Early Spring Bird Activity on the Farallon Islands, California. -Of the numerous published accounts of the birds of the Farallon Islands, few are based on observations made in the winter. Through the courtesy of the United States Coast Guard I spent several days, January 12 to 16 and March 17 to 23, 1960, on the Southeast Farallon Islands which are situated about 28 miles west of the Golden Gate Bridge, San Francisco, California. The primary purpose of my visit was to determine the winter activity of Cassin Auklets (Ptychoramphus aleutica). Each evening Cassin Auklets were noted coming in from the sea in large numbers about an hour and a half after sundown. In January no eggs were found, but the birds were active cleaning out old burrows. In some instances new burrows were begun in the soft soil, and many birds were engaged in mating activity. Burrows started on January 14 were incomplete; on March 18 they were approximately 30 inches in length. Mr. Ralph Gingles and Mr. Steven Brewster, resident Coast Guard personnel, informed me that the “night birds,” as they call them, were first heard under the buildings during the last week of December of 1959 and that they returned in large numbers early in January. Their return in December coincides with the first heavy rain after the dry season. The rain appears to facilitate burrowing by dampening the soil. Dry soils cave in readily.

Upon arrival at the island the auklets immediately entered their burrows and began their subterranean activity. Between 10 and 11 p.m. most of the activity ceased and the auklets returned to sea. A few remained later, but by 2 a.m. the sounds of the auklets were rarely heard. This is in contrast to the full activity observed in March when the auklets demonstrated the greatest activity between midnight and dawn. On March 22 birds incubating eggs were present in approximately one-third of the nests examined.

In addition to this early nesting activity of the auklets in January, five Ashy Petrels (Oceanodroma homochroa) were found feeding young. All five young were fully feathered and almost ready to leave their nests in the rock walls. The young petrels were first discovered when I saw adults fly into a rock wall at about 9 p.m. on January 13 ; the feeding calls of the young were subsequently heard. This observatioti confirms the assumption made by Orr (Condor, 46, 1944: 125-126) that the nesting of this species extends into mid-winter. On March 17, Ashy Petrels were numerous, occupying nesting holes, and were actively engaged in mating. This observation extends the breeding season to approximately 10 months on the Farallon Islands, or from about the middle of March to the middle of January.

In January numerous resident Rock Wrens (Salpinctes obsoletes), 10 to 12 Robins (Twdzts migratorius), 7 Western Meadowlarks (Sturnella neglecta), 1 Red-shafted Flicker (Colaptes cafer), 1 Sparrow Hawk (Falco sparverius), 1 Belted Kingfisher (Megaceryle alcyon) , ancl 2 Killdeers (Chad&s vociferzts) were the conspicuous land birds noted. Recorded near the islands were flocks of Red-necked Grebes (Podiceps grisegena) .--AM C. THORESEN, Department of Zoology, Oregon State College, Corvallis, Oregon, April 4, 1960. 

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