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

Road Surveys
Road surveys involve driving slowly along a
road, typically after sunset, and watching for
animals. Such surveys are a common method
for estimating distribution and abundance
of herpetofauna and are recommended for
augmenting species lists (Shaffer and Juterbock
1994).
Field Methods
We focused mainly on the Cactus Forest Loop
Drive and also drove Speedway Boulevard from
Douglas Spring Trailhead to the intersection with
Tanque Verde Loop Road and Camino Loma
Alta from the trailhead to Old Spanish Trail. We
recorded each individual detected by species
and whether animals were alive or dead. We
surveyed 29 April – 18 August 2001 and 9 – 14
July 2002 during nights and occasionally during
evenings.
Effort
We conducted 55 road surveys totaling 46.3 hours
of effort (Table 4.2).
Analysis
Because survey routes varied in length and
included a number of different segments surveyed
in various orders, we combined results from
all routes and road segments. Total mileage
for each route was not recorded so we scaled
estimates of relative abundance by time. We
calculated relative abundance as the number
of individuals detected for each species (or all
species combined) per hour of effort. We also
compared relative abundance of species groups
across months using ANOVA and linear contrasts.
We log (x + 1) transformed relative abundance to
improve normality.
Incidental Observations
We noted sightings of rare or important species
by sex and age/size class (if known) and recorded
time of observations and UTM coordinates
for all detections. These incidental detections
were often recorded before or after more formal
surveys and we use these sightings to determine
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species presence and richness. We also used
incidental sightings from other field crews (e.g.,
birds).
Species Identification Challenges
Whiptail lizards (Cnemidophorus [Aspidoscelus
by some sources] spp.) are notoriously difficult
to identify in the field because of the similarity
in appearance for several sympatric species
(Stebbins 2003). Many parthenogenetic (nonsexually
reproducing) whiptails may have arisen
as hybrids from the same diploid, sexually
reproducing parent species (Degenhardt et al.
1996). Several undescribed “parthenospecies”
may exist in the desert Southwest (Wright and
Vitt 1993, Cole and Dessauer 1994). Some
individuals we identified as western (C. tigris) or
Sonoran spotted (C. sonorae) whiptails may be
undescribed “species” related to these recognized
species.
In the district we saw “classic” Sonoran
spotted whiptails (adults with six longitudinal
dorsal stripes, light spots in dark and occasionally
light dorsal areas; dorsal stripes more yellow
anteriorly; overall color brown dorsally and
unmarked white-cream ventrally; tail more
brownish-orange than bluish as seen in Gila
spotted whiptails; Degenhardt et al. 1996, Phil
Rosen pers. obs.). We also observed a variation
of this classic appearance that superficially
resembled Gila spotted whiptails, with some
captured individuals keying out to be this
species based on characteristics noted in field
guides, including number of pre-anal scales,
location of spots in light stripes, and greenish tail
(Stebbins 2003). Although the Rincon Mountains
are considered outside the range of the Gila
spotted whiptail, in this document we report
these individuals as this species, and report the
“classic” Sonoran whiptails described above as
Sonoran spotted whiptails.
Results
We detected 46 species of herpetofauna; seven
amphibians and 39 reptile species (Appendix