The Ecology of Tijuana Estuary, California: An Estuarine Profile

nciude the l~ttle blue heron (Flortda caerulea).
tricolored heron (Hydranassa tricolor) and black
sk~mmer (Rynchops nrgra) The black skimmer
recently began to nest at the salt ponds of south
San Drego Bay. that population is the only breeding
one in the western United States (Whits, pers
comrn Its use of Tiluana Estuary as a foraging
area shows that brrds resrding in one wetland may
rely upon several others for survival The best
wetlands for birds may be those where a variety of
wetland habttats are available nearby
Figure 42. The great blue heron Mclntrre collectton,
capyright 1986 by Zedler
endangered bird, the peregrine falcon (Faico
peregrtnus anaturn). has been reported from the
estuary
In all, 298 bird species have been recorded in
Tijuana Estuary and river valley (Whtte and
Wunderlrch, unpubl) Of these, 69 are found
prlrnarrly within the estuarine habitat, 144 occur
mainly in adjacent upland and riparian habitat, and
85 specres are found in both habitats In 1973-74,
a census of the northern section of Tijuana Estuary
revealed that the following 15 birds were most
abundant willet, marbled godwit, western
sandp~per (Cal[drls rnauri), least sandpiper (Cal~drrs
rntnutrtla), dow~tcher (Lfrnnodromus spp 1. Belding's
Savannah sparrow, house finch (Carpodacus
rnexfcanus), white-w~nged scoter IMelan/tta fusca).
f legant tern (Sterna elegans), Northern pintall
(Anas acuta) ring-billed gull (Larus delawarensfs),
black-bellied plover (Pluv~alus squalarola).
Forster's tern (Sterna forsterd and long-billed
curlew (Whrte and Wunderllch, unpubt ) With the
exception of the house ftricil an3 possibty the
ring-brlled guli, ali of these species forage tn
estuar!ne channels
Several water-assoc~ated birds that are rare tn
Californra are often seen at Ti~uana Estuary These
Channels are ~mportant foraging habitats for a
var~ety of b~rds from other habitats Beld~ng's
Savannah sparrows rely on tidal creek and channel
edge habitats for feeding Clapper rail foraging
behavior has been discussed In Section 3 3
Feeding studies of California least terns (Minsky
1974, Atwood and Minsky 1983) document feeding
rn nearshore waters, as well as estuarine channels
and bay habitats Preferred ftshes include northern
anchovy, topsmelt, and jacksmelt (Ather~nops
calrforn~ens/s) Brecdrng adults catch and feed
these small ftsh (4-9 cm long) to the chicks The
young begin to fly at about 20 days of age and the
fledgl~ngs devciop faraging skills in calm. protected
waters "Even estuar~ne and freshwater IocaliEies
that are d~stant from active nesting sltes liiay be
heav~ly used by least terns during post-fledgling
dispersal, loss or disturbance of such areas may
reduce the survrvorshtp of dependent young"
(Atwood and Minsky 1983)
3.7 INTERTIDAL FLATS
The conspicuous species of the sandflats and
mudflats are the shorebirds that feed and rest
there during low tide (Figure 43) Most of their
invertebrate food species were discussed in
Section 362
Many of the prey animals are
distributed from the subtidal channels to the lower
llmrt of the sait marsh
Four invertebrate species that are characteristic
of exposed flats are the California horn snalt, the
yellow shore crab, the ftddier crab and the lined
shore crab (Figure 43) There are no quantitative
data on any of these at Tijuana Estuary We know
only that the horn snails can be extremely
abundant (hundreds to thousands per square
meter), and that both horn snails and crabs are
rmportant foods for the clapper rail (Jorgensen
1975) It IS l~keiy that all these species were
negatively affected by estuarine closure rn 1984
Lafge numbers of empty horn snail shells were
collected from the mudfiat adjacent to the ~niand
!agoom in 1984 only an accastonai Itve ~ndtvidual
was found Lined shore crabs were found dead
and floating in the hypersaline water durtng 1984
Our discussron emphasrzes the shorebrrds that
were studred extensively in 1979-80. Boland