Assessing the potential of habitat manipulations as a conservation strategy for eastern
massasauga rattlesnakes, Sistrurus catenatus catenatus
Brent D. Johnson, SUNY-ESF
Final Report to Edna Bailey Sussman Foundation, December 2012
Background
The eastern massasauga rattlesnake (EMR), Sistrurus catenatus catenatus, is listed as
threatened or endangered throughout most of its range. Along with draining and development of
their wetland habitats, reforestation through natural succession is now threatening EMR
populations in the northeastern United States by reducing essential basking opportunities.
Habitats that allow for thermoregulatory behavior are crucial for survival of EMRs, especially
pregnant females that require basking to ensure proper -development of their young.
At Cicero Swamp Wildlife Management Area, New York, an endangered population of EMRs
has faced rapid succession of open-canopy habitats to tall woody shrubs and forest. The New
York State Department of Environmental Conservation (DEC) recently carried out extensive
manipulations at the site in an effort to increase suitable basking habitats for pregnant female
EMRs. In 2011, their work entailed cutting of shrub vegetation to create 32 100-m2 basking plots
and forest to produce a 10-acre clear-cut and two 5-acre thinnings. In 2012, they added 12 28.3m2 basking plots. They sought to provide cuts that would not only be used by EMRs but would
offer optimal basking conditions. A previous study at Cicero Swamp found basking site selection
by EMRs to be a trade-off between exposure to high environmental temperatures and avoidance
of potential predators, or crypsis. Therefore, both environmental temperatures and crypis
potential measurements serve as an indicator of basking habitat quality. My graduate research
involves assessing the potential of habitat manipulations as a means of conserving EMRs at
Cicero Swamp. Implications of this research could extend to management of snake or reptile
populations elsewhere that are threatened by woody encroachment. I sought support of a
Sussman Foundation Internship to further evaluate the DEC’s manipulations through a second
season of examining use of cut areas and through assessing succession patterns and variables not
measured in my first season.
In order to suggest a plan for long-term maintenance of high-quality basking sites at Cicero
Swamp, my specific objectives have been to 1) assess changes in habitat use by EMRs in
response to habitat manipulations and 2) evaluate the quality of the manipulations over time. I
also intend to use mark/recapture data from 2006-2012 to 3) provide baseline estimates of
growth, survival, and reproduction for the Cicero Swamp population. These estimates could be
compared to future estimates in order to see if habitat manipulations have had a true impact on
the conservation status of the EMRs.
2012 Accomplishments
With the aid of two field assistants, I regularly surveyed plots of different cut dates – 2008, 2011,
2012, and uncut (control) – for EMRs from May 21 to August 27, 2012 to evaluate their use. We
used models to measure the variables indicating basking site quality – daytime environmental
temperatures and crypsis potential – among plots (Figure 1). Outside of the field, we used
ArcGIS 10 software to classify habitat types in the core range of EMRs at Cicero Swamp in a
series of past aerial images (Figure 2). The nine images used ranged from years 1938-2011.
Since the end of the field season, I have computed probabilities of change among the classified
images to understand past succession at the site and estimate future succession of basking
habitats under various management scenarios. We caught all EMRs we found throughout the
field season and marked new individuals for permanent identification via injection with a Passive
Integrated Transponder (PIT) tag (Figure 3). All previously marked and newly marked female
individuals found contributed to the established mark/recapture data set.
A
B
Figure 1. (A) Temperature models, constructed from painted copper pipes containing dataloggers,
recorded hourly environmental temperatures of plots throughout the summer. (B) We examined a PVC
model from standing height within random locations of plots to measure their crypsis potential.
A
B
Figure 2. Two examples of aerial image classifications of the core range of EMRs at Cicero Swamp
representing years (A) 2009 and (B) 2011. Dark green (5) represents coniferous trees, green (4) signifies
deciduous trees, light green (3) is high shrub areas, and off-white (0) shows DEC manipulations. The
white diamond shape and larger ovals near the bottom are ponds removed from each image.
B
A
C
Figure 3. (A) We found EMRs among the hummocks and hollows of the wetland habitat. (B) We caught
each new EMR to obtain measurements of length, mass, etc. and (C) to injected it with a PIT tag for
permanent identification.
Preliminary Results
Statistical analyses suggest that EMRs used 2012 plots significantly more than 2011 cut plots
and used each of these more than 2008 or control plots under warmer temperatures. No specific
cut date of plot was preferred when temperatures were cool. Forest clear-cut plot surveys
resulted in a single EMR sighting. Average daily environmental temperatures and crypsis
potential measurements indicate the quality of the plots of different cut dates, with ones cut
2012, 2011, and 2008 being suitable basking sites (Figure 4). I have used classified images to
provide a visual representation of past succession at Cicero Swamp (Figure 5) and to calculate
transitions probabilities which I have used to project future succession under 20 or more habitat
manipulation scenarios. Estimates associated with survival, growth, and reproduction of the
EMR population at Cicero Swamp are still forthcoming.
Figure 4. Average daily environmental temperature and crypsis potential of plots
of different cut dates. Dotted lines indicate the lowest of each variable preferred
by EMRs. Bars on points show 95% confidence intervals.
Figure 5. Proportions of habitat types over time in the core range of EMRs
at Cicero Swamp, indicating rapid succession in the past half century.
Preliminary Conclusions
EMRs select recently cut habitats over other areas for basking when air temperatures are optimal.
EMRs did not readily move from established basking areas into adjacent forest clear-cut or
thinnings. The quality of cut plots as cryptic basking sites persists through at least three years of
vegetation re-growth. Continued manipulation of basking habitats may be a suitable conservation
strategy for EMRs of Cicero Swamp in the future as cut plots provide suitable habitat that
pregnant females use, potentially allowing for more proper development of their young.
Implications of this work could be extended to the management of snake or other reptile
populations elsewhere faced with succession of their crucial habitats.
Acknowledgments
Thanks to the Edna Bailey Sussman Foundation for providing me support to conduct a second
field season at Cicero Swamp to acquire much more data necessary for completing my Master’s
research project. Thomas Bell of the Department of Environmental Conservation has given
valuable recommendations and other assistance, helping me to conduct my research in the best
way possible for providing useful information back to the DEC. I appreciate the opportunity the
DEC as a whole has given me to work on this fulfilling project. James Gibbs, my advisor, has
given me great guidance and encouragement throughout all of our time spent working on the
project thus far.