Vascular Plant and Vertebrate Inventory of Saguaro ... - USGS

Cumulative number of species
70
60
50
40
30
20
10
0 5 10 15 20
Creek where many of the large riparian trees
are in poor condition (Powell 2004); some
loss of riparian bird species may have already
occurred. For example, the yellow-billed cuckoo
and song sparrow, both riparian obligate birds
are common in nearby Cienega Creek (Corman
and Magill 2000), and there is no reason to
believe that with healthier riparian vegetation
these species would not be found along Rincon
Creek as well. The current drought has certainly
affected the health of the riparian system. The
decline in the amount and timing of surface water
availability is also likely affected by the recent
increase in groundwater pumping supplying the
explosive growth of housing and commercial
development in the Rincon Valley (see Chapter
2). Because birds are so closely tied to vegetation
characteristics, the loss and degradation of large
riparian trees will mean a reduction in the number
of species and abundance of some riparianobligate
birds along the creek. The threat of
losing groundwater and (by extension) surface
water to development, recently prompted the park
to file in-stream flow water rights in an effort to
ensure the long-term viability of the riparian area.
They have also initiated studies of the plant and
Sample period
Figure 5.6. Species accumulation curve for line-transects for birds, Saguaro National
Park, Rincon Mountain District, 2002-2003. Each sample period is a randomized
combination of approximately 50 observations.
65
vertebrate communities of the area (e.g., Powell
2004).
Housing developments in the Rincon
Valley, in particular, will also likely affect the
bird community through an increase in nonnative
(rock pigeon, European starling, and house
sparrow) and human-adapted species (e.g., the
great-tailed grackle, mourning dove, house finch,
and brown-headed cowbird). The increase in
density of human-adapted species invariably
follows housing developments and these changes
usually lead to the decline in densities of nonhuman-adapted
species, especially in the areas
immediately adjacent to development (Mills et
al. 1989, Germaine et al. 1998). Mannan and
Bibles (1989) suggest a number of ways to reduce
the impact of non-native bird species on the
district’s wildlife including (1) limiting density of
housing near the district boundary, (2) reducing
the number of horses, (3) limiting sources of open
water, and (4) limiting landscaping with nonnative
plants, especially lawns. Many of these
measures are effective in reducing native, humanadapted
species as well.
An increase in nearby housing may
facilitate the spread of non-native plants, which