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

surveys (yellow-breasted chat and house sparrow;
Table 5.5). We observed only four species
(brown-crested flycatcher, mourning and whitewinged
doves, and western tanager) at > 50 of the
transects. This is in contrast to the repeat-visit
VCP surveys (Appendix G) and is likely because
by visiting a station only once, we missed species
that would probably be recorded on subsequent
surveys.
Line-transect Surveys
We found 63 species during line-transect surveys
in the winter of 2002 and 2003 including six
species that we did not record during VCP
surveys (Appendix C). We found the most
species along the Lower Rincon Creek transect
(n = 45) and fewest along the Douglas Springs
transect (n = 31; Table 5.6). The chipping
sparrow was the most abundant species on two
transects. All three of the most abundant species
on the Upper Loma Verde transect (chipping
sparrow, green-tailed towhee, and Brewer’s
sparrow) did not breed in the Sonoran Desert
region, whereas the three most abundant species
along the Lower Rincon Creek transect (blackthroated
sparrow, cactus wren, and Gambel’s
quail) did breed in the district. Two of the three
most abundant species along the Douglas Springs
transect (chipping sparrow and western bluebird)
did not breed in the district.
Nocturnal Surveys
We recorded nine species during nocturnal
surveys of nine transects (Table 5.7). We found
the most species along the Rincon Creek and
low-elevation transects combined, though survey
effort was greatest there (Table 5.2). The most
abundant species within a stratum was the elf owl
in the low-elevation stratum (Table 5.7). Only
two species were found only in a single stratum
and no species were found in all three. The
great-horned owl was found in the low- and high-
elevation strata and was certainly missed in the
middle-elevation stratum.
57
Incidental and Breeding Observations
We observed 154 species during incidental
observations, including 13 species that we did
not record during other surveys (Appendix C).
We made 288 observations of 78 species that
confirmed breeding in or near the district (Table
5.8). Of these we found 104 nests of 48 species
including a nest of the sulphur-bellied flycatcher
near Happy Valley Saddle. We found two
instances of brown-headed cowbird parasitism:
one blue-gray gnatcatcher feeding a fledgling
cowbird and one Bell’s vireo nest with a cowbird
egg.
Inventory Completeness
The bird survey effort at the Rincon Mountain
District of Saguaro National Park was the most
comprehensive of the eight park units surveyed
by the UA inventory group. We made over
15,000 observations and found 85% (n = 173)
of the species that had been found previously
in the district (Appendix C), and found 10 new
species. These results are unprecedented in the
Sonoran Desert Network, and are especially
important given the large size and diversity of
communities and difficult access issues in the
district. Considering all of the other research and
site-specific inventory efforts in the district (see
review at the beginning of the chapter), we are
confident in concluding that at least 90% of the
species that regularly occur in the district have
been recorded.
The species accumulation curve for our
research (from all surveys combined; Fig. 5.4)
shows the number of new species dropping off
significantly at approximately halfway through
the inventory. After the first half of the surveys,
we found only an additional 8% (n = 14 species)
of the species found in the entire effort. A closer
look at the species accumulation curve for repeatvisit
VCP surveys reveals that the Riparian
community had the most complete inventory,
though the other communities show signs of
reaching an asymptote, particularly the Conifer
Forest community (Fig. 5.5). There is a similar
pattern for the line-transect surveys (Figure 5.6).