(Agelaius phoeniceus) commonly set up 

 territories in the tall, dense vegetation, and 

 dragonflies (Odonata: Anisoptera; Figure 

 3.15) are obvious insect inhabitants. 



At Tijuana Estuary, the areas of brackish 

 marsh appear to have formed artificially 

 following hydrologic and topographic 

 modifications. The 1928 air photo (Figure 

 2.6) indicates that natural brackish marsh 

 may have been present at the inland lagoon 

 before a channel was dredged to make the area 

 tidal. Before 1900, the area would have 

 supported brackish marsh if sufficient 

 rainwater accumulated or if seepages were 

 present.- In the absence of continual brackish 

 or freshwater inputs, the depression would 

 probably have been an alkali sink colonized by 

 brackish species during wetter periods. 



Brackish marshes are now found west of 

 the airfield, at the abandoned gravel pits, 

 where rainfall accumulates, and at the south- 

 ern end of the estuary, where sewage spills 

 from Mexico through Goat Canyon provide an 

 intermittent water source. The braided 

 channels of the Tijuana River support ephem- 

 eral patches of brackish marsh, but their 

 location and longevity relate to recent flooding 

 and to spills of sewage or irrigation water. 



The function of these brackish habitats 

 relative to the estuarine ecosystem is under 

 debate. Further north, there is evidence that 

 springs were frequent around the intertidal 

 wetlands, and various restoration plans have 

 called for the creation of large areas of fresh- 

 to-brackish marshes (e.g., State Coastal 

 Conservancy plans for Orange County wetlands 

 and for restoration of Los Cerritos Wetland). 

 Much of the presumed value of brackish 

 marsh habitats comes from studies of Upper 

 Newport Bay (Zembal and Massey 1981a), 

 where the State's largest population of light- 

 footed clapper rails persists. Rails use both 

 brackish and salt marsh habitats at Upper 

 Newport Bay and at San Elijo Lagoon, and the 

 nontidal brackish marshes are a likely refuge 

 for the birds during high water. Thus, the 

 proximity of several small brackish marshes 

 along the periphery of saline marshes may 

 improve conditions for rails. The cause- 

 effect relationships need to be tested, not just 

 for rails, but for the variety of brackish and 



saline marsh species. Furthermore, the 

 reciprocal interactions, i.e., the use of saline 

 marshes by brackish species, need to be 

 investigated. 



On at least one occasion, brackish marsh 

 species expanded into the estuary under 

 nontidal conditions. During the 1984 closure, 

 red-winged blackbirds moved into the lower 

 salt marsh and set up territories in the 

 cordgrass. Their effect on native salt marsh 

 birds (e.g., Belding's Savannah sparrows and 

 clapper rails) was not assessed, but it should 

 be before recommendations are made to add 

 brackish marshes along the periphery of 

 Tijuana Estuary salt marsh. Such 

 experimental work would be possible if 

 artificial fresh, brackish, and saline marshes 

 were constructed at the Pacific Estuarine 

 Research Laboratory (Chapter 6). 



Fresh and brackish marshes may function 

 as a general refuge for animals when the 

 estuary has high water. It has been assumed 

 that the Dairy Mart Road Ponds, about 5 km 

 upstream of Tijuana Estuary, are used by 

 estuarine birds, because many species are 

 seen in both localities. These ponds occur in 

 areas where gravel mining has left large pits; 

 the water source is both river flow and ground 

 water. Black-crowned night herons (Nycti- 

 corax nycticorax; Figure 3.16), black-necked 

 stilts (Himantopus mexicanus), American 

 avocets (Recurvirostra amehcana; Figure 

 3.17) and snowy egrets (Egretta thula) are 

 conspicuous among these tree-lined ponds. 



Boland's (1981) data on shorebirds in 

 Tijuana Estuary support the concept that 

 ponds provide alternative resting and feeding 

 sites during high tides. He compared bird use 

 in the intertidal flats with that of the river 

 and the inundated salt pannes at the southern 

 end of the estuary. Of the 21 shorebird 

 species Boland studied at Tijuana Estuary, 10 

 used both the river and pool habitats for 

 feeding (Table 3.4). Nearby, in the blocked 

 channel (an area that was once tidal), 

 different birds, including black-necked stilt, 

 phalaropes, and willets were commonly found 

 feeding Heavy use of these nontidal areas by 

 waders, sandpipers, and plovers shows that 

 estuarine shorebirds are not restricted to 

 intertidal habitats. 



43 



