mouse, deer mouse, and house mouse (Mus 

 musculus) were all trapped in areas with 

 glasswort and pickleweed present, especially 

 around salt pannes. The highest densities 

 were recorded in spring (up to 75/ha). Deer 

 mice were dominant, with 59% of the 

 captures. Western harvest mice comprised 

 31%, and the remainder were house mice. 



The higher salt marsh (Figure 3.3) is one 

 of the most complex wetland communities, 

 because it is subject to alternating 

 environmental extremes of drought and 

 inundation, because disturbance is frequent, 

 and because its topography is sometimes 

 mounded. Eighty-six mounds that ranged from 

 9 to 57 cm in height and 5.6 to 18.6 m in 

 diameter were characterized in 1984 (Cox 

 and Zedler 1986). Each "island" of higher 

 topography allows species of the higher marsh 

 to extend farther into the wetland. The marsh 

 periphery is thus patchy and diverse; the 

 larger the mound, the longer the plant species 

 list. In addition, the mounds provide habitat 

 for several herbivorous mammals, which in 

 turn influence mound and intermound 

 vegetation. 



Cox attributes the mound formation to 

 ground squirrels and other burrowing 

 mammals that use the high ground. He 

 suggests that over centuries, they gradually 

 transport soils toward a central burrow 

 opening until a pattern of mounds and 

 intermound areas is created. Whether the 

 concentration of squirrels on mounds is cause 

 or effect, however, is hard to demonstrate in 

 short-term studies. What is clear is that the 

 mounds of high ground, which are surrounded 

 by wetter marsh, add small-scale habitat 

 diversity to the wetland. Where adjacent 

 areas have been filled or developed, these 

 islands provide the only clue to the higher- 

 elevation communities that might have 

 occurred in the transition zone. The invasion 

 process can be seen in wet winters, such as 

 1983, when high spots are leached of their 

 salts and upland weeds (e.g., the wild radish, 

 Raphanus sativum) germinate and grow. Such 

 salt-intolerant species rarely persist beyond 

 the next dry season. 



Herpetofauna are likewise limited to these 

 areas of high ground. The San Diego horned 



lizard (Phrynosoma coronatum blainvillei; 

 Figure 3.4) is declining because of frequent 

 collection, but a few remain in isolated areas. 

 Snakes are not common, and their rarity 

 partly explains the abundance of rodents such 

 as ground squirrels (Spermophilus beechyii) 

 and rabbits (Lepus californicus and 

 Sylvilagus audubonii sactidiegi) that populate 

 the upper marsh. 



Birds that feed and/or nest in the high 

 marsh include the white-crowned sparrow 

 (Zonotrichia leucophrys), song sparrow 

 (Melospiza melodia), western meadowlark 

 (Sturnella neglecta), and killdeer 

 (Charadrius vociferus). Other birds use the 

 area extensively for foraging. Raptors, such 

 as the northern harrier (Circus cyaneus), 

 American kestrel (Falco sparvehus), and 

 golden eagle (Aquila chrysaetos), exploit the 

 populations of small mammals; while 

 Belding's Savannah sparrows, horned larks 

 (Eremophila alpestris), and loggerhead 

 shrikes (Lanius ludovicianus) feed on insects 

 and other small prey (A. White, SDSU, pers. 

 comm.). 



The vegetation and soils of the upper 

 marsh support many insects, spiders, and 

 mites, but few other invertebrates (Figure 

 3.5). Tachys corax, literally the swift raven, 



Figure 3.4. The San Diego horned lizard. 

 Mclntire collection, © 1986 by Zedler. 



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