Details - CALS Networking Lab - University of Arizona

near intensive plots, but most were in areas we
thought would have high species richness, species
of special interest, or species suspected to be in
the district that had not previously been recorded
(e.g., the rock rattlesnake). Extensive surveys
were more flexible and allowed for variation in
survey time and area. For road and extensive
surveys, we surveyed in evenings and nights to
detect species with restricted activity periods
(Ivanyi et al. 2000). Although we designed
methods to detect both amphibians and reptiles,
we detected fewer amphibians because they
have more limited activity periods and are often
restricted to aquatic environments, which are rare
in the district.
Intensive Surveys
Field Methods
At focal-point transects (hereafter “transects”)
in 2001, we used plot-based visual encounter
surveys constrained by time and area (Crump
and Scott 1994) along 17 transects (Figs. 4.1,
4.2). Along each transect we surveyed within
the confines of three 1-ha (100 x 100 m) subplots
during spring (9 April - 24 May) or two subplots
during the summer monsoon (18–31 July) and
searched each subplot for one hour. We surveyed
only two subplots in summer because there
was not sufficient time during peak activity
periods to search all three subplots. Although
Focal
Point
Transect
line
1000 m
28
we surveyed all 17 transects in spring only seven
transects were surveyed in summer and these
were located only in low (n = 3) and middle (n
= 4) elevation strata. We selected survey times
that coincided with periods of peak diurnal
reptile activity because activity levels vary with
temperature (Rosen 2000). On cooler spring days
we began our surveys between 0718 and 1421
hours whereas on hotter, summer days we began
between 0642 and 1014 hours. To account for
within-day variation in detectability and to reduce
variation among observers, we surveyed each
subplot twice per day by a different observer. We
did not survey during evenings or nights.
We searched subplots visually and aurally
and worked systematically across each subplot
and used a Garmin E-map GPS to ensure we
stayed within subplot boundaries during surveys.
We also looked under rocks and litter and used
a mirror to illuminate cracks and crevices. For
each animal detected, we recorded species, sex
and age/size class (if known), and microhabitat
(ground, vegetation, rock, edifice, burrow, or
water). We marked subplot corners with rubbercapped
stakes and recorded UTM coordinates
with a Trimble GPS. We recorded temperature,
wind speed (km/h), percent relative humidity,
and percent cloud cover using hand-held Kestrel
3000 weather meters (Nielson-Kellerman Inc.,
Boothwyn, PA) before and after surveys. We also
described vegetation and soils.
Plot Number
1 2 3 4 5 6 7 8 9 10
Figure 4.1. Layout of herpetofauna survey plots along focal-point transects, Saguaro National Park,
Rincon Mountain District, 2001. We typically surveyed three, 100 x 100 m subplots (dotted boxes) in the
spring and two subplots (1 and 10) in the summer. When topography prevented surveys in a subplot, we
surveyed an adjacent subplot.
100 m
100 m