|
California Clapper Rail cont. most important characteristics of high quality rail habitat. Rails feed on invertebrates in the mud of the channels during lower tides. The channels are rich in food resources because constant supplies of nutrients enter the marsh with each tide cycle. Generally, marshes with more tidal channels can support more rails because food resources are more abundant. Rails in the tidal channels are also fairly safe from most predators because most channels are too narrow to allow predators to hunt effectively. If pursued in a channel, rails will evade predators by running quickly down a channel system and taking cover in the overhanging vegetation of the channel, becoming nearly impossible to capture. Most predation of clapper rails takes place during higher tides, when the tidal channels are filled with water and most marsh vegetation is flooded. This happens mostly during the winter season, when very high tides are common. The elevation of the marsh greatly affects which type of vegetation will grow, determining how rails can use the marsh. Low marsh areas with sparse vegetation and tidal sloughs are used by rails for foraging. Higher marsh areas with dense vegetation are used for nesting. A marsh needs to have both high and low marsh in order to supply all the needs of the rail. Marsh elevation has been a problem in many past (and present) restoration projects because of limitations in the methods used to construct the marsh. Since most of the restorable parcels in the San Francisco Bay area have subsided due to drying of the soil after being diked off from the bay, elevations in many parcels are currently too low to support marsh vegetation. The two main methods of raising the level of restoration sites are introduction of dredge spoils (bay muds) on top of the existing soil surface and opening the area up to tidal action and allowing natural sedimentation to raise the ground level. Both methods are still experimental and may be subject to problems. When using dredge spoils, it is difficult to predict how much material should |
Last updated:
May 22, 2008
|