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Figure 5.2. Diagram of infrared-triggered camera (Trailmaster) set-up. Image based on Swann et al. (2004).
Trailmaster Cameras
We used infrared-triggered cameras (herein
referred to as “Trailmaster”; Trailmaster®; model
1500, Goodman and Associates, Inc, Lenexa, KS;
Kucera and Barrett 1993) to record the presence of
medium and large mammals. Trailmasters have
three components: receiver, transmitter, and camera
(Fig. 5.2). The transmitter sends an infrared beam
to the receiver at a specified rate (5 times per
second for this study). The receiver then sends a
signal (via cable) to a camera mounted on a tripod
6–8 m away. When an animal blocks the infrared
beam the camera takes a picture.
We set the receiver and transmitter
approximately 8 m apart and 20 cm above the
ground so that medium and large mammals were
captured on film but smaller animals such as
rodents and birds were not. We set cameras to take
no more than one photograph every five minutes to
reduce the chances of recording the same
individual more than once (on the same occasion).
We placed cameras in three areas of the park (Fig.
6.1; UTM coordinates for Willow Gulch = 644390
N, 3558289 E; Apache Spring = 647101 N,
3557644 E; Visitor Center Road = 647729 N,
3557866 E) that we thought would record the
highest number of species; typically these were in
areas of dense vegetation. We baited camera sites
with a commercial scent lure (ingredients included
synthetic catnip oil, bobcat musk, beaver
castorium, and propylene glycol as a preservative)
or canned cat food. We checked cameras
approximately every two weeks to change film and
batteries and to ensure their proper function. We
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photographed a placard documenting the date and
camera location on the first exposure of every new
roll of film.
Spatial Sampling Design
We selectively placed cameras in areas that we felt
would have the most success, primarily near
Apache Spring.
Effort
We operated Trailmaster cameras at three locations
from May 2002 to May 2003 for a total of 278
days of camera operation (Table 5.1). Of the three
locations, Apache Spring had the most effort
(47%), followed by visitor center road (38%) and
Willow Gulch (15%).
Analysis
Trailmaster cameras are the most cost-effective
method for recording the presence of medium and
large mammal species (Kucera and Barrett 1993,
Cutler and Swann 1999). However, one drawback
to this method is an inability to differentiate
individuals, which precludes any estimates of
abundance (i.e., one must be able to determine
whether one animal has been photographed
repeatedly or whether more than one individual has
been photographed). In some cases, size or
physical abnormality may differentiate individuals
of any species, but this was not evident in our
photographs. Also, each species is more or less
likely to be attracted to the camera area. Therefore,
we report the number of times a species was
photographed to indicate species that may be
common, based on the number of photographs.