Portal de Periódicos da CAPES

The Seasonal Occurrence of Shorebirds on Bay Farm Island, Alameda County, California

1951; Oxford University Press; Volume: 53; Issue: 4 Linguagem: Inglês

10.2307/1364875

1938-5129

Robert W. Storer,

Avian ecology and behavior

The mud flats on the north and west parts of Bay Farm Island, Alameda County, California, are known as one of the major shorebird concentration areas in the San Francisco Bay region; and, although the island has been visited frequently by ornithologists, to date no one has published an account of the seasonal variation in abundance of the shorebirds there.For this reason the shorebirds on these parts of Bay Farm Island were censused for a year beginning July 1, 1948.In order to learn something about the habitat preferences of the species of shorebirds involved, the area suitable to shorebirds was divided into ten parts and the numbers of birds found on each sub-area (fig. 1) were recorded on mimeographed census sheets.Some of these sub-areas were found to attract few or no shorebirds and consequently were seldom visited.The most important feeding area (B) was a large mud flat surrounded by dikes on the north and west, by Maitland Drive on the east, and by Island Road (also known as Mecartney Road) on the south.Until 1940 this area was farm land, but at the time of the census all except the south edge, which supported a salt marsh flora with Salicornia predominating, lay between the zero and five-foot tide levels.At the south side of B there was an artificial sand bar (F) with a small pond on its south side.The bar remained uncovered during all but the highest high tides and was sometimes' used as a loafing area by gulls, terns, and shorebirds.The second most important feeding area for shorebirds on the island included the mud flats (A) of San Leandro Bay, from the Bay Farm Island Bridge east to a point north of the pond (J), a distance of approximately one mile.This area was bordered on the south by a band of salt marsh of which Spartina and Salicornia were the dominant plants.There was a chain of islands covered with similar vegetation on the northeastern part of this area.These marshy areas were used as loafing grounds by some of the larger species of shorebirds.The mud flats of .thesoutheast side of the Island of Alameda lay across a narrow channel from A, and there was some interchange of feeding shorebirds between these two' areas.At the northeast corner of the junction of the bridge with Bay Farm Island, there was a small sandy area (C) .The sand was mixed with stones, and during part of the year a growth of green algae covered much of the area, thereby changing its character considerably.Across the road from C was a dike (L) which was largely gravel overlying mud.Beyond the inlet at the west end of L a similar section of dike had been cut off from the rest of the dike and served as a roosting and loafing area for many birds, particularly gulls and terns.The water level in the sandy-clay bordered pond (J) varied little, and this pond proved to be a favored place for Greater Yellow-legs, Northern Phalaropes, and Killdeer, which tended to remain there throughout the day regardless of the conditions on the mud flats.The pond was also regularly visited by flocks of Dowitchers and Avocets on their way to or from their feeding grounds.The pond (K) at the edge of the Alameda Dump was filled with and bordered by tin cans and bottles.An occasional Killdeer, Yellow-legs, or Snipe was seen there.Three small, cattail-bordered ponds (G, H, and I) on the golf course were apparently not suited for use by shorebirds.The south and west shores of Bay Farm Island were bordered by intertidal areas of fine sand mixed with mud.These were occasionally visited at D and E, but there were never many shorebirds feeding there.