The Ecology of Tijuana Estuary, California: An Estuarine Profile

Figure 20. The upper marsh habitat with the California ground squirrel, salt marsh bird's beak (lower left), boxthorn,
prickly pear, golden bush (behind the ground squirrel), and glasswort and shore grass (in front of the ground
squirrel). A northern harrier is silhouetted above the horiz
In a few places at Tijuana Estuary, the
endangered salt marsh bird's beak (Cordylanthus
maritimus ssp. maritimus; Figure 20) occurs in the
higher marsh. Because it is an annual, it is evident
only for a short time during the spring and summer
growing season, and because the plants are small,
it is easiest to spot when in bloom (April-June). It
is thought that this annual plant can survive the
warm dry summer without frequent tidal
submergence because it is hemiparasitic. Its roots
develop haustoria that penetrate a variety of other
species to gain water and nutrients.
Subpopulations of bird's beak are highly dynamic,
sometimes spreading, sometimes disappearing for
a year or more. A little disturbance appears to
open habitat for seediing estabiishrnent
(Vanderweir 19831, and the activities of mammals
may be an important part of the plant's ecology.
However. too much disturbance (e.g., repeated
trampling, soil compaction) prevents surv~val, and
habitat destruction near urban development is Figure 21. The San Diego horned iizard. Mclntire
probably a major cause of its endangered status. collection, copyright 1986 by Zedler.
21