Amphibian Monitoring in the Canyon Country of the Colorado Plateau
February 2004
At least 13 amphibian species are found on the Colorado Plateau, although some have very limited
distributions in this bioregion. Amphibian declines have been documented in many parts of the world,
but knowledge of amphibians on the Colorado Plateau is inadequate to determine population status
or trends for most species. We have yet to even delineate distribution across the Colorado Plateau
for some species, much less be able to state whether a species is declining. At present, we do not
know of acute threats to most amphibians on the Colorado Plateau, however, habitat loss is a chronic
problem as it is in most places.
The central portion of the Colorado
Plateau was selected to be part of
the USGS Amphibian Research and
Monitoring Initiative, and we are now
developing monitoring methods that
will work in areas where amphibian
habitat is ephemeral in time and
space. Identifying breeding habitat
for amphibians on the Colorado
Plateau is difficult because most
breeding sites, even in cañons,
arroyos and washes, are not
permanent bodies of water, and the
animals are only active for brief
periods of the year. Thus, we have a
very small window of time in which to
survey a large and rugged area for
the presence of amphibians. We are
trying to streamline this effort by
identifying potential habitat in
advance (i.e., when neither water
nor amphibians are present) in order
to know where to conduct surveys
when conditions are right.
Our monitoring program is designed
to document the Proportion of
habitat Areas Occupied (PAO) by
amphibians. This is a metric being
tested by ARMI, and entails
surveying randomly selected habitat locations and recording where amphibian species are found. If
amphibians are not found, it may be because they are actually absent from the site, but can also be
because they were simply not detected by surveyors. Re-visiting sites provides additional data to help
estimate the detectability or probability of finding an amphibian if it is, indeed, present at a site.
By selecting our sites at random within a
monitoring area, we can extrapolate PAO
estimates across a larger landscape and assess
the status of each amphibian species for the
entire monitoring area. As data are collected over
years, trends in habitat occupation by amphibians
can be estimated as well. This information is
important for resource managers in the National
Park Service, Bureau of Land Management, and
U.S. Forest Service to effectively manage and
protect amphibian species on the Colorado
Plateau.
We have been working on protocols for
monitoring amphibians within the Canyonlands
National Park survey area since 2001. We began
with an area-based method of selecting survey
sites. The entire area (approx. 3050 km2) was
divided into 32 subareas (based on hydrologic
reporting units), and 12 were selected at random
for survey on a rotating basis (3 each year for four
years before the first three would be re-surveyed).
Each unit must be surveyed at least twice within
the activity period of the amphibians to determine
the detection rate for each species.
Surveying hydrologic units
involves covering large areas
of non-habitat. Since most
amphibian habitat on the
Colorado Plateau occurs in
drainages, we are now
concentrating survey efforts
along drainage courses (i.e.,
solid or dashed blue lines), as
depicted on USGS 7.5'
quadrangle maps. We use a
Geographic Information System
to partition all drainage courses
into 500-meter segments, then
randomly select about 10% of
the segments for surveying.
The advantages of this
approach are that field efforts
are oriented toward the areas
of the landscape where most
amphibian habitat occurs,
drainage segments take less
time to locate in the field than
points away from drainages,
and traveling up and down
drainages (e.g. canyons,
arroyos, etc.) is usually easier
than trying to move across the
rugged landscape (i.e., we gain
increased efficiency for surveys
and re-visits). There are
disadvantages to this
technique. Because the
"blue-line" approach limits
surveys to drainages, the
statistical universe to which our
data apply is also limited to the
drainages of the Canyonlands
survey unit.
Breeding habitats outside of drainages (e.g., potholes, rock pools, stock ponds, swales in undulating
topography, and wet meadow pools) are not included as potential habitat to be surveyed. Not all
drainages contain habitat (e.g., 22% of segments surveyed in 2003 contained no amphibian habitat),
so we still lose time surveying non-habitat, but less than before. We are still working on the temporal
dynamics of amphibians on the Colorado Plateau relative to requirements of using PAO. We may
have to exclude the summer monsoon activity period in order to meet constraints on repeat visits for
PAO. We are working to resolve these issues as we continue in the protocol development phase of
the project. Full implementation of a Colorado Plateau monitoring program is anticipated to begin in
2005 or 2006.
In 2003, we surveyed 94 drainage segments in the Canyonlands survey area. We also surveyed a
few segments in Arches National Park (12) and Natural Bridges National Monument (8) to evaluate
whether the sampling approach worked equally well in smaller parks. We found amphibians in only
23 segments (15 in Canyonlands, 1 in Arches, and 7 in Natural Bridges). We re-visited 43 of the
segments to determine species detection rates. There were no cases of finding amphibians on the
second visit that were not already detected on the first visit.
The National Park Service Northern Colorado Plateau Network (NCPN) has provided additional
funding for us to refine these survey protocols, after which we will expand our monitoring area to
include core parks of the NCPN: Canyonlands, Arches and Capitol Reef National Parks, and
Natural Bridges National Monument. In addition, we are exploring the possibility of expanding our
efforts to include Glen Canyon National Recreation Area, as well as the Grand Staircase-Escalante
National Monument and other lands administered by the Bureau of Land Management.
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