Population Studies of Tidal Marsh Breeding Birds at Rush Ranch: A Synthesis

Abstract

Rush Ranch, with the largest contiguous area of fully-tidal marsh remaining in northern Suisun Bay, is critical habitat for a number of endemic bird species that breed in brackish tidal marsh. Despite the abundance of non-native invasive plants (particularly perennial pepperweed, Lepidium latifolium) and altered hydrology, it is the best remaining representative in Solano County of the tidal marsh that once covered more than 27,000 ha (67,000 acres) in Suisun Bay. This paper presents a synthesis of bird population studies conducted at Rush Ranch since the late 1970s, concentrating on California clapper rail (Rallus longirostris obsoletus), California black rail (Laterallus jamaicensis coturniculus), Suisun song sparrow (Melospiza melodia maxillaris), common yellowthroat (Geothlypis trichas), and marsh wren (Cistothorus palustris). These studies indicate declines in clapper rail abundance, when we compared the past 8 years to surveys conducted 10 to 25 years ago. However, black rails appear to be increasing at Rush Ranch, and overall in Suisun Bay. Nest monitoring of reproductive attempts by song sparrows conducted between 1996 and 2005 indicates low overall nest survival rates, mainly from high predation rates, but also great year-to-year variability. Low nest survival rates of tidal marsh song sparrows observed at Rush Ranch appear to be too low to sustain populations, and such low rates are consistent with the apparent population declines observed for this subspecies at Rush Ranch. Nest survival and other components of reproductive success of tidal marsh birds should be monitored in the future to provide information on ecosystem condition and population health, as well as the response of these species to management, including control of non-native plant species.