The Ecology of Tijuana Estuary, California: An Estuarine Profile

Table 14. Early information on dune vegetation at Silver Strand, the beach that extends
north from Tijuana Estuary (from Purer 1936b). Species present in 1936 and their
common names are listed. Taxonomy follows Munz (1 974) and (USDA 1982).
Species present
Arnbrosta mantlrna ragweed "one of the most consp~cuous plants forms
extensive mats along the dunes as well
as ~nland where the sand is unstable'
Abronta urnbellata sand verbena "grows In more stablllzed place in the sand
strand form~ng extensive mats'
Ambros~a charn~sson~s dune ragweed "holds a conspicuous and ~mportant
place In unstab~lized areas'
A triplex leucophylla salt bush "forms hummocks of sand assoc~ated
w~th Abron~a and Ambrosra"
Caktle edentula sea rocket "f~nds ltself at home close lo the ocedn a
Cam~sson~a cherranthtfol~a
ssp suffrutlcosa dune prrrnross 'fluor~shes on the [pla~n] of the strand'
Carpobrotus aequrla terale seaf ig 'a consp~cuous ieature of the landscape
Gasoul nod~florum
G cryslail~nurn
~ce plant
'quite well cf~str~buted"
forms large mats'
Rhus ~nteqr~lolra lemonadeberry 'growlng extensively on the strand ~n
many places growth IS cons~derably
stunted to a mere few Inches'
pecles hds been entlruly replaced by C rnarlljrna, whtch was dbserl! in 1936
open sand areas. Two rare species nest on the have bred {Massey and Atwood 1984). The
dunes of Tijuana Estuary, and a variety of other estimates of nesting pairs have ranged from 21 to
species feed on the sandy shores adjacent to the 66 in the past 4 years (Table 15). Factors such as
dunes.
winter mortality have not been examined but could
help to explain annual variations The 1984
The Federally endangered California least tern closure of T~juana Estuary to tidal flushing may
(Figure 48) nests in depressions In the sand along have adversely affected recruitment In 1984,
the dunes Their eggs and chicks are vulnerable to about 50 palrs nested but no fledglings were
a number of terrestrial and avian predators. as well observed. The stagnant channel water and
as accidental or intentional disturbances by corresponding reduction in fish and invertebrate
humans. If the first clutch fails, adult least terns populations may have contr~buted to nesting failure
miry attempt to nest again. The least tern 1s a (L. Copper, ornlthologtst, pers comm)
cofaniat nesting species that prefers sandy dunes
with low amounts of dune vegetation and debris
(less than 3%; M~nsky ei. a1 1983). Females lay an
Also nesting on the dunes IS the relatively rare
snowy plover (Figure 48). This bird is not a
average of two eggs in a small depression Or
scrape in the substrate Young are fed exclusively
coionial nester but often associates with colonies
of Calriornra least terns (White, pers. comm.)
on fish by both parents. Young least terns fledge Snowy plovers lay an average of three eggs.
at 3 weeks, and they gradually learn to feed on Chicks leave the nest within 24 hours of hatching
their own in lnland lakes and estuar~es
and ~mrned~ately follow the parents to foraging
areas along the sandy shoreline and mudflats.
The number of nesting pairs at Tijuana Estuary Snowy piovers feed rnarnly upon invertebrates
fluctuates widely from year to year, as at other nest along the water's edge on the sandy shoreline.
sites that are unprotected from predatton and While less well studied than the least tern colonies,
human disturbance. Adult terns breeding for the the snowy plover breeding population at Tijuana
first time do not show a clear preference for therf
natal colonies but tend to return to a site once they
Estuary is observed annually during least tern
censusing (Copper, pers. c0mm.)
56