ContentsPutah and Cache: Willow Slough and Creeks' Ends

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Birds of Putah-Cache: Valley Floor

John Kemper

From the viewpoint of the birds, the Sacramento Valley floor is the most important part of the watershed, because it provides wintering habitat for an amazing range of species. Prominent among these, of course, are the waterfowl—swans, geese, and ducks. In November and December, the tundra swans and greater white-fronted geese arrive in the wetlands of the Yolo Bypass, and at times may number in the tens of thousands. By January, most have moved on to areas further south. Other major winter residents are American coots, mallards, gadwalls, cinnamon teals, northern shovelers, canvasbacks, lesser scaups, and ruddy ducks. The most abundant duck in winter is the northern pintail.

Numerous species of herons and egrets are prominent in the flatlands. These include the great egret and snowy egret, both of which are entirely white, highly visible, and present year-round. Less visible are the marsh dwellers, especially black-crowned night-herons. The night-herons are seldom seen because they forage at nighttime, but in the winter one to two thousand of them roost along the water-supply canals of the Conaway Ranch in the Yolo Bypass. According to Christmas bird counts taken annually by the Audubon Society, this population may be the largest concentration of black-crowned night-herons in the country. In the spring, the night-herons nest in dense colonies in many places in the region, in marshlands, willow thickets, and eucalyptus groves.

In the wintertime, the Sacramento Valley holds concentrations of raptors, such as red-tailed hawks and American kestrels, that are among the largest in North America. These flatlands are the heart of the population of white-tailed kites, which are infrequent in other parts of the country but prominent here year-round. Another important raptor is the Swainson's hawk, which is classified as "threatened" in the State of California. Swainson's hawks are present only during the summer, and migrate to Mexico and South American for the winter. The flatlands between Putah and Cache creeks are a major breeding habitat, and the narrow riparian fringe at Willow Slough is their major nesting location in the region.

Shorebirds are also heavily represented on the valley floor. Killdeers, black-necked stilts, and American avocets are major nesters. During fall migration, beginning in August, shorebirds of many species come through, but have a difficult time finding shallow muddy areas for foraging in the dry season. The artificially-created Davis Wetlands just east of the city's wastewater treatment plant provides valuable habitat at this water-scarce time of year.

In August and September, hundreds of tiny, inconspicuous shorebirds known as phalaropes flock to open water areas such as the Davis Wetlands and the ponds at the local wastewater treatment plants. Long-billed dowitchers show up in force in late August, and remain in large numbers throughout the winter.

During spring migration, when a lot of water with muddy margins is present, the numbers of shorebirds passing through the Yolo Bypass can be staggering, especially including species such as black-bellied plover, dunlin, western sandpiper, and least sandpiper.

No recounting of the birds of the valley floor would be complete without mentioning its most famous resident-yellow-billed magpie. The yellow-billed magpie is one of only two true endemics in California, the word "endemic" meaning that the species is found no place else. (The other true California endemic is the island scrub-jay, found only on Santa Cruz Island, off the southern coast of California). The yellow-billed magpie is found only in Central California, and is most abundant in our part of the Central Valley.

Present on the valley floor in great numbers in winter, but generally overlooked because they are so common, are flocking species such as western meadowlark, white-crowned sparrow, savannah sparrow, horned lark, American goldfinch, and various blackbirds. Among the blackbirds is the tricolored blackbird, which is almost a California endemic, and has been considered for listing as a threatened species.

Two other sensitive species inhabit the flatlands, burrowing owl and mountain plover. The major hazard confronting burrowing owls is urban development, and the conversion of the their foraging habitat to cultivated fields. Some still remain in the relatively undisturbed pastures and flatlands of the valley floor, but they are on the decrease.

By contrast, mountain plovers are attracted to Yolo County's farmland, especially just after the fields have been plowed, but they, too, are in decline. In a survey conducted in 1994, about 3,300 birds were counted statewide, but in a similar survey in 1998 the total had declined by 25 percent. These winter residents may soon be listed here as "threatened," due to pressures on their breeding habitat in Montana, Wyoming, and Colorado.

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