200 -i 



CO 



■g 



> 



c 



•s 100 H 



as 



E 



3 



1 984 



1 979-80 



- c Ht- 



in 

 <o 



omomoinom 



••S-Tj-lOmtDCDI^I^- 



r r i 



O ID O 

 GO GO O 



r r P P 



ID 

 CT) 



in o in 



o *- i- 



o in o in 



CM CM CO CO 



o in o m o 



* * Id II) (O 



Standard Length (mm) 



Figure 3.23. Length-frequency distributions for topsmelt collected in Tijuana Estuary in fall and 

 winter, 1979-80 (Nordby, SDSL), unpubl. data) and fall 1984 (C. Donohoe, SDSU, unpubl. data). 



3.6.5 Birds 



The channels of Tijuana Estuary are 

 important foraging and resting areas for a 

 variety of bird life such as great blue herons 

 (Ardea herodias), which prey upon channel 

 fishes (Figure 3.24). Shorebirds forage 

 primarily for invertebrates in the sand and 

 mud sediments and in the water column; 

 diving birds prey upon fishes; wading birds 

 use both fishes and invertebrates for food 

 sources while others, such as dabbling ducks 

 and plovers, feed on vegetation and surface 

 insects, respectively. Three Federal 

 endangered and one California endangered bird 

 species use channel organisms for prey. 

 These include the California least tern, the 

 California brown pelican (Pelecanus 

 occidentalis californicus), the Light-footed 

 clapper rail, and the Belding's Savannah 

 sparrow. Other bird species that feed on 

 fishes in the channels are the belted 

 kingfisher (Megaceryle alcyon) osprey 

 (Pandion haliaetus), and double-crested 

 cormorant (Phalacrocorax auritus). 



Several water-associated birds that are 

 rare in California can be seen at Tijuana 

 Estuary. These include the little blue heron 



Figure 3.24. The great blue heron. Mclntire 

 collection, © 1986 by Zedler. 



57 



