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Effects of Prescribed Fire on Montane
Rattlesnakes: Endangered Species and
Ecosystem Restoration
Andrew T. Holycross, Senior Research Associate, Biology Department,
Arizona State University, Tempe, AZ; L. J. Smith, Research Assistant,
Biology Department, Arizona State University, Tempe, AZ;
C. W. Painter, Herpetologist, New Mexico Department of Game and
Fish, Santa Fe, NM; and M. E. Douglas, Curator, Biology Department,
Arizona State University, Tempe, AZ
U
sing radio telemetry, we evaluated the effects of the Maverick Prescribed
Fire on mortality and behavior of three montane rattlesnake species (One
Crotalus molossus, five C. lepidus, and three C. willardi obscurus) in the Peloncillo
Mountains of Arizona and New Mexico. Of particular concern were effects on
federally threatened C. w. obscurus or its habitat. The Peloncillo population of C.
w. obscurus is one of three island populations [the Sierra San Luis (Sonora and
Chihuahua) and Anirnas Mountains (New Mexico) contain the other two populations]. Before this study, 11 C. w. obscurus had been documented in the Peloncillo
Mountains-eight of these within the primary fire perimeter and three within the
secondary perimeter.
Radiotelemetry was performed between 5 May and 30 July 1997 within the
primary perimeter at two locations approximately 3 km apart. Following surgical
in1plantation of transmitters, snakes were released at point of capture and located
once every day for a total of 483 observations. Observations were brief( <10 min.)
to minimize disturbance. Location was recorded using a handheld Global Positioning System (GPS) receiver (Trimble Geo Explorer II). Data were stored as
GPS files and mapped from differentially corrected Universal Transverse Mercator
(U.T.M.) coordinates. Each snake's milieu was categorized as:
(a) subterranean (deep within a refuge, may or may not be visible);
(b) cavity/crevice (near the surface, <50% ofbody exposed); and
(c) above ground (>50% ofbody exposed).
Observations were divided into three periods: A = initiation of telemetry to
time fire affected each snake; B = post-fire to onset of monsoon ( 17 July 1997);
and C =onset of monsoon to end of study (30 July 1997).
The north site burned 24-25 June. The fire was particularly intense on slopes
and ridges where high fuel load and prevailing winds enhanced pre-heating and
convection. On the plateau, where fuel load was reduced due to recent grazing
and previous fires, a less-intense fire left some areas unburned. At the south site,
fire on 27 June was of lower intensity and resulted in a mosaic of burned and
unburned areas. At each site, all snakes were located <18 hours pre-fire and <24
hours post-fire. Eight snakes exposed to low-intensity fire survived, while a snake
exposed to intense fire died. Pooled data on spatial descriptors of snake activity
(daily activity area, movement rate, movement magnitude) showed no significant
differences in pair-wise comparisons of activity before and after the fire (Wilcoxon's
USDA Forest Service Proceedings RMRS-P-10. 1999.
109
Effects of Prescribed Fire on Montane Rattlesnakes: Endangered Species and Ecosystem Restoration
Holycross, Smith, Painter, and Douglas
Signed-Rank Test, P>O.OS). However, snakes moved significantly less frequently
after the fire (Wilcoxon's Signed-Rank Test, N=8, P=0.04) and were found in
subterranean retreats more frequently after the fire than before the fire (Figure l ).
Wooded canyons and wooded steep slopes burned intensely because of high fuel
accumulation, resulting in habitat loss for C. w. obscurus. This snake is exceptionally scarce in the Peloncillo Mountains, with habitat naturally fragmented into
isolated canyons. This form may thus represent a metapopulation, with low levels
of interdemic migration and gene flow. If isolated demes are extirpated,
recolonization from adjacent canyons may take decades, even if vegetative recovery is rapid. The fate of each habitat patch is thus critical to conservation of this
threatened rattlesnake. While reintroduction of fire is essential in maintaining a
mosaic of habitats and ecosystem function, fires intense enough to effect type
conversion may have severe long-term consequences for C. w. obscurus populations. Prior to reintroduction oflarge-scale summer fires, consideration should be
given to reducing unnaturally high fuel loads to preserve C. w. obscurus habitat
and reduce mortality.
Figure 1. Milieu of nine radio
tagged rattlesnakes during each
of three periods of observation:
A=before fire; B=between fire
and monsoon season; C=after
onset of monsoon season. For
periods A, B, and C, n = 289,
125, and 69 observations respectively.
100
80
60
%
40
20
0
Period A
D
Above ground
•
Subterranean
Period B
Period C
Cavity
Acknowledgments
We thank Holly Blankenship, Geoff Cook, Tom Devitt, Brian Fedorko, Andy
Holland, Eric Koeck, Richard Phillips, James Sifert, Jesus Sigala, and Bryan Starrett
for assistance in the field. Linda Allison, Larry Clark, Jim Hatton, Jeff Howland,
Sally Lanier, Sharon Lohr, Pu Shen, and Bob Reed provided help with GIS, software, and analysis. Financial support was provided by the Malpais Borderlands
Group, Wallace Foundation, Nongame Branch of Arizona Game and Fish Department, Endangered Species Program of New Mexico Department of Game
and Fish, Coronado National Forest, and USDA Forest Service Rocky Mountain
Research Station. Specimens were collected and radio tagged under permits to
ATH: AGFD-SP7ll300, NMGFD-2824, and USFVVS-PRT6768ll. Surgical implantation of transmitters was approved by ASU Institutional Animal Care and
Use Committee (IACUC) protocol no. 93-280R.
110
USDA Forest Service Proceedings RMRS-P-10. 1999.