The implications of Cape Sable seaside sparrow demography for Everglades restoration

The Cape Sable seaside sparrow is a Federally listed endangered species end emic to south Florida's Everglades. It nests near the ground in seasonally dry prairies. Consequently, the timing and depth of seasonal water flows de termine its fate. With water management plans the central focus of Everglad es' restoration schemes, the demography of this bird becomes central to hyd rologic planning. In order to understand how its demography influences rest oration options, we calculated survivorship, fecundity and dispersal within three of the sparrow's six populations. Nearly 40% of adult sparrows die f rom year to year. Sparrows can produce up to four broods per breeding seaso n, and typically produce two (March to August). Females lay an average of t hree eggs per nest, two of which usually hatch. The success of these nests varies among populations such that nests in population E are more than four times as likely to fledge young as nests within population A. Nest success within population B is 26% early in the breeding season, but drops to 9% a fter the onset of summer rains in early June. Nests are built 16 to 21 cm f rom the soil surface making them vulnerable to water depths that exceed the se values. Based on observations of marked individuals, sparrows generally remain within a I km area centred on their breeding grounds. We have never observed immigration between populations. A simple demographic model demons trates that breeding success and duration appear to constrain sparrow popul ation growth more than other demographic parameters. Maintaining suitable b reeding conditions restricts water management options to those that will re store hydrological conditions to their original patterns.