December 2010
(Frequently Asked Questions)
Florida panthers (Puma concolor coryi)
have been listed as an endangered species since 1967 in recognition
of its small population size and geographic isolation (USFWS 2008).
References to panther numbers have appeared in scientific
literature, agency outreach materials, and popular media for years.
Historically, most statements regarding Florida panther numbers
have resulted from expert opinion, informed by field observations
of those most closely engaged in panther research. Various figures
have been used throughout the years, including 20-30 throughout the
1970s and early 1980s; 30-50 in the late 1980s through the
mid-1990s; 50-70 for a few years following genetic restoration in
1995; and since 2000, 90-120 panthers.
This "Clarification Document" is intended to:
- provide a better understanding of the difficulties in
developing a rigorous population estimate with statistical
confidence;
- describe the methods currently used by the Florida Fish and
Wildlife Conservation Commission (FWC) to provide an indication of
approximate population size; and
- provide an estimated upper bound for the number of adult
panthers in south Florida.
Rigorous capture-mark-recapture methods (CMR) used
to develop population estimates, including DNA hair snares and
trail cameras, have been effective for bears or felids with
uniquely identifiable fur coloration patterns, respectively.
Unfortunately, preliminary testing has shown that panthers are not
consistently attracted to hair snares to make this a dependable
method to obtain a robust population estimate, and it is not
possible to reliably identify individual panthers via their fur
(they are not spotted or striped). In addition, CMR sampling
techniques are labor intensive and expensive when implemented for
carnivore populations that occupy large areas. This includes
panthers, which occupy a breeding range of 2.2 million acres. These
issues have similarly affected how managers attempt to estimate
puma population sizes in the western United States. Population
estimates are determined using a mix of educated guesses, hunter
take, or in some cases, they are not estimated at all (e.g.,
Wyoming uses trend data to inform management). Nevertheless,
discussions regarding CMR methods and panther population estimates
warrant additional dialogue as we move forward.
There are two methods that have been developed that
provide a structured approach to informing expert opinion:
- Annual Counts - This method was developed by
Roy McBride and was published in the Southeastern Naturalist
(McBride et al. 2008). McBride, and staff of Ranchers Supply,
collect data on verified panther sign and conduct field surveys to
tally a minimum number of panthers detected by calendar year
(Figure 1). The technique provides an annual count based on panther
sign, tracks, panthers treed by dogs, and those outfitted with
radio transmitters. The method does not provide confidence
intervals associated with the count's precision, does not account
for annual variation of sampling effort, nor does it provide
estimates of the numbers of missed or double-counted panthers.
McBride et al. (2008) acknowledges that about one-quarter of
occupied panther range exists on private lands and that these
properties were not surveyed. Figure 2 tracks the most recent
annual counts compiled by Roy McBride of Ranchers Supply.
- Minimum Number of Panthers Known to be Alive -
This method was developed by Darrell Land and is compiled using
both live captured panthers as well as panthers discovered at
time-of-death (primarily roadkills). Each panther is aged at first
encounter and then that individual is counted as a member of the
population back in time to when the cat was estimated to be at
least 1 year-of-age. For example, if a panther estimated to be 5
years old is encountered in 2010, it was born in 2005. That panther
is tallied for the years 2006, 2007, 2008, 2009 and 2010. This is
repeated for all panthers and then summed by year (Figure 3).
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Because it is retrospective and the most recent
years' tallies increase as new animals are discovered, this method
does not provide a good measure of current minimum panther numbers;
therefore, we only show data through 2008. It is important to
remember that this methodology only tallies panthers that were
known or estimated to be more than 1 year of age and alive at some
point in the respective calendar year. The number should not be
reported as a population estimate but rather the minimum known
number of panthers. The actual number of panthers is undoubtedly
higher because not all panthers are captured or found dead.
Neither of these two methodologies provides a true
population estimate and neither provides an estimate of variance.
Additional research is necessary to determine the most robust and
repeatable method of estimating the size of the panther population.
The U.S. Fish and Wildlife Service and the FWC are contracting with
biometricians and wildlife biologists to further explore the use of
camera trap data. Camera trapping shows some promise for providing
a statistically robust way to monitor population trends using
panther occurrence data and occupancy models; whether these models
will yield true population estimates remains to be determined.
The Ranchers Supply annual panther count and the
FWC's minimum number of panthers count both indicate that panther
numbers have increased since 1995. Both counts suggest that we
currently have a minimum of at least 100 panthers.
However, we can calculate an upper bound for the
number of panthers based upon a combination of data from the 2009
Ranchers Supply annual count and the size of occupied panther
habitat in South Florida.
We started by calculating the total area of four of
the nine sampling units utilized by Ranchers Supply, Inc.
(2009):
- Big Cypress National Preserve (BCNP) south of I-75 and north of
US 41;
- Fakahatchee Strand Preserve State Park and Picayune Strand
State Forest;
- Florida Panther National Wildlife Refuge; and
- BCNP north of I-75 and the Big Cypress Seminole Indian
Reservation.
These four units form a large, consolidated block
of panther habitat with shared borders. These units are adjacent
and similar in habitat composition to areas that were not surveyed
by McBride (2009). The combined area of these four units was 3283.7
km2. McBride (2009) counted a total of 58 adult panthers within
those units in 2009, thereby yielding a density estimate of 0.0177
panthers per square kilometer (1.77 panthers per 100 km2), a value
within a range of densities described by Logan and Sweanor (2001).
As stated earlier, McBride (2009) does not provide estimates of the
number of missed or double-counted panthers but this count does
constitute the best available information on panther numbers. We
believe our density estimate may represent a higher value relative
to other Ranchers Supply, Inc. (2009) units because it was
calculated within units that constitute the core of panther range.
Using a higher-than-average density estimate was deemed acceptable
because this exercise was intended only to provide an upper bound
for panther numbers.
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A paper published in 2006 by Kautz et al.
delineated an area, referred to as the Primary Zone that was
supporting the panther population at that time. Applying this
density estimate to the Primary Zone (9189 km2) yields an upper
estimate of 163 adult panthers. Therefore, (and rounding our
numbers to the nearest increment of 10), FWC staff believes that
the boundaries of the current adult panther population size is
approximately 100-160 within the Primary Zone. It is recognized
that there is considerable variability of habitat throughout the
range and actual panther density would be dependent upon habitat
type and habitat quality. The upper bound of 160 is based on the
idealized and unlikely premise that the high panther density found
in the core range would be found across the entire variable habitat
of the Primary Zone. Nevertheless, this provides reasonable
boundaries of a minimum and maximum population to provide some
insight into the possible magnitude of the adult population size in
this area of Florida. We are hopeful that future advances in
estimating panther numbers will allow us to provide a rigorous
population estimate with statistical confidence and improved
precision.
Literature Cited
Kautz, R., R,Kawula, T. Hoctor, J. Comiskey, D.
Jansen, D. Jennings, J. Kasbohm, F. Mazzotti, R. McBride, L.
Richardson and K. Root. 2006. How much is enough? Landscape-scale
conservation for the Florida panther. Biological Conservation
130:118-133.
Logan, K. A., and L. L. Sweanor. 2001. Desert puma:
evolutionary ecology and conservation of an enduring carnivore.
Island Press, Washington.
McBride, R.T., R.T. McBride, R.M. McBride and C.E.
McBride. 2008. Counting pumas by categorizing physical evidence.
Southeastern Naturalist 7:381-400.
Ranchers Supply, Inc. 2009. Florida panther annual
count 2009. 147pp.
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