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

(2) Receiver
triggers
camera to
take picture
Camera
Receiver
white-tailed and mule deer) are difficult to
distinguish under poor light conditions or if
only part of the animal is visible; for these we
made the best possible attempt to distinguish
them, and sometimes identified the individual
to genus only.
We entered these and other data
(species, number of individuals, film number,
location, date, time if available, bait, etc.)
into an Access database. For each random
area and for each point we summarized the
number of species and number of individuals
photographed. To create species distribution
maps, we converted UTM coordinates to NAD
83 datum and imported them into ArcView.
Comparing species abundance and
presence among locations using infraredtriggered
photography is problematic. As
with all methods, animals may not be detected
because they are absent, or because they were
present and not detected. In addition, rates
of detection undoubtedly vary greatly among
species. Determining relative abundance can
also be difficult. Infrared-triggered camera
units often do not operate continuously
between the time they are set and when they
are next checked because the roll of film may
be entirely exposed, or because the unit may
fail due to technical problems or field errors.
To estimate rates of detection based on effort,
we used dates on photographs to determine as
closely as possible how many days a camera
unit was operating for each roll of film, then
summed the number of operational days at
each location. Where dates were not available
for a roll of film, we substituted the mean
number of days it took to fill a 36-exposure roll
of film (11.8 days).
We compared species richness among
the three elevation strata and between random
77
Infrared beam
Transmitter
(1) Animal blocks infrared
beam from getting to receiver
Figure 6.8. Typical configuration for an active infrared-triggered camera system. Image based on Swann
et al. (2004).
Table 6.2. Summary of infrared-triggered camera effort, Saguaro National Park, Rincon
Mountain District, 1999–2005. See Appendix K for more complete summary.
P= Number of camera nights
Location type Elevation stratum Number of cameras Sum Mean SD
Non‑random Low 58 2162 37 40.4
Middle 5 200 40 33.6
High 11 294 27 18.8
Random Low 36 515 14 5.9
Middle 44 523 12 8.2
High 21 201 10 6.1