combination of stresses: reduced food 

 supplies, poor cover, and lack of predator 



protection. 



Light-footed clapper rails are considered 

 to be generalists in terms of feeding, but 

 direct observation and dissection of 

 regurgitated pellets shows that the majority 

 of foods come from channel and tidal creek 

 habitats: marine decapods, isopods, snails, 

 crabs, fishes, and some insects and spiders 

 (Massey and Zembal 1979). With the 1984 

 drought, invertebrate populations declined, 

 rails had few prey available, and starvation is 

 a likely cause of bird mortality. Declining 

 cover during the nesting season may have led 

 to nesting failure by reducing the area of 

 dense cordgrass for nest construction and by 

 making nests and birds more visible to 

 predators. Finally, the absence of tidal 

 flushing greatly reduced protection from 

 predators. Few mammals frequent habitats 

 where tides saturate the soils twice a day, but 

 in summer and fall 1984, there were few 

 natural deterrents to terrestrial predators. 

 Birds that had little cover and low food 

 supplies would no doubt have been highly 

 susceptible to predation; chicks would have 

 been easy prey for dogs, cats, and raptors. 



The population crash at Tijuana Estuary 

 was not permanent, but it did not recover 

 immediately after dredging restored tidal 

 flushing (in December 1984). The birds 

 reestablished on their own, but it is not clear 

 where they came from. The population 

 increased from 2 pairs in 1986 to the 1991 

 peak of 47 pairs. Recovery was not steady, as 

 the 1987 high count of 23 pairs was followed 

 by 61% drop to 14 in 1988. It is too soon to 

 tell whether the population will stabilize or 

 what level constitutes the carrying capacity of 



the system. Active management to maintain 

 tidal flow is necessary but apparently not 

 sufficient. 



The decline of the entire southern 

 California population from 277 pairs in 

 1984 to 142 pairs in 1985 is only partly 

 explained (i.e., 20%) by tidal closure at 

 Tijuana Estuary. There were heavy losses in 

 other wetlands that remained open to tidal 

 flushing (Zembal 1991, Figure 3.31). It is 

 likely that most of the region's clapper rails 

 were reduced by mortality, rather than 

 emigration, as alternative habitats are few 

 and far from the coastal wetlands. The birds 

 are found in the marshes of Estero de Punta 

 Banda near Ensenada, Mexico. Habitat has also 

 declined at this wetland, with a large part of 

 the bay being dredged for construction of an 

 oil-platform factory. 



The future of the light-footed clapper rail 

 is uncertain. With such a large fraction of the 

 population at one site (54% at Upper Newport 

 Bay), a major flood or predator invasion 

 (e.g., red fox) there could have devastating 

 impacts regionwide. The subpopulation at 

 Tijuana Estuary offers a unique opportunity 

 for enhancement first because it is fairly 

 large and may retain significant genetic 

 diversity, and second because there is ample 

 room for restoration of its preferred habitat, 

 cordgrass and tidal creeks. The tidal 

 restoration plan (cf. Chapter 6) could open 

 hundreds of acres of nearby, relatively dry 

 habitat to clapper rails. The greatest 

 potential for increasing clapper rail numbers 

 is to increase the area of suitable habitat at 

 sites that already have rails present and that 

 are managed to sustain tidal flows. Tijuana 

 Estuary has the most potential for such 

 enhancement. 



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