Site by Bennett Web & Design Co.
Proceedings of the 4th Big Thicket Science Conference
2009 Southeastern Naturalist 8(Special Issue 2):41–46
Texas Ratsnake Predation on Southern Flying Squirrels in
Red-cockaded Woodpecker Cavities
D. Craig Rudolph1,*, Richard R. Schaefer1, Josh B. Pierce1, Dan Saenz1,
and Richard N. Conner1
Abstract - Elaphe spp. (ratsnakes) are frequent predators on cavity-nesting birds
and other vertebrates, including Glaucomys volans (Southern Flying Squirrels).
They are known predators of Picoides borealis (Red-cockaded Woodpeckers), especially
during the nestling phase. Picoides borealis cavities are frequently occupied
by Southern Flying Squirrels, often several squirrels per cavity. Behavioral aspects
of ratsnake predation on fl ying squirrels in woodpecker cavities is an important
component required for a full understanding of the potentially complex interaction
between Red-cockaded Woodpeckers, Southern Flying Squirrels, and ratsnakes. We
induced previously captured Elaphe obsoleta (Texas Ratsnake) to climb boles of
pine trees and gain access to Red-cockaded Woodpecker cavities known to contain
Southern Flying Squirrels, and observed the resulting predatory interactions. Eight
of nine ratsnakes successfully captured 14 of 22 Southern Flying Squirrels present
in the cavities.
Picoides borealis (Vieillot) (Red-cockaded Woodpecker), Glaucomys
volans L. (Southern Flying Squirrel), and Elaphe spp. (ratsnakes) have a
close interacting relationship involving cavity use and predator-prey interactions
in the fire-maintained pine forests of the southeastern United States
(Conner et al. 1996; Kappes 2004, 2008; Laves and Loeb 1999; Mitchell et
al. 1999; Rudolph et al. 1990a, b). Red-cockaded Woodpeckers excavate
cavities used by all three taxa, and Southern Flying Squirrels are competitors
for Red-cockaded Woodpeckers cavities. In turn, ratsnakes are predators on
both woodpeckers and squirrels. However, the impact of these interactions
at the population level and appropriate management responses in relation to
the endangered Red-cockaded Woodpeckers are subject to debate (Conner
et al. 2001; Kappes 2004, 2008; Rudolph et al. 1990b, 2004; Walters 1990;
Withgott et al. 1995).
Elaphe spp. frequently attempt to climb trees containing Red-cockaded
Woodpeckers cavities, especially during the nesting season (Jackson 1974,
1978; Neal et al. 1993). Elaphe spp. are also potential predators on secondary
cavity users of Red-cockaded Woodpecker cavities. Based on frequency
of use, Southern Flying Squirrels would presumably be the most important
1Wildlife Habitat and Silviculture Laboratory (maintained in cooperation with College
of Forestry, Stephen F. Austin State University), USDA Forest Service, Southern
Research Station, 506 Hayter Street, Nacogdoches, TX 75962. *Corresponding author
42 Southeastern Naturalist Vol. 8, Special Issue 2
potential prey species. Given the importance of the interaction between
Red-cockaded Woodpeckers, Southern Flying Squirrels, and ratsnakes, additional
information on specific aspects of this interaction is desirable. Here
we report the results of climbing trials of Elaphe obsoleta (Say) (Texas
Ratsnake) on trees containing Red-cockaded Woodpecker cavities occupied
by Southern Flying Squirrels and the resulting predation attempts.
Materials and Methods
The study was conducted in Red-cockaded Woodpecker cavity tree clusters
on the Angelina and Davy Crocket National Forests in eastern Texas.
The habitat was Pinus palustris Mill. (Longleaf Pine) or P. taeda L. (Loblolly
Pine)/P. elliotii Engelm. (Shortleaf Pine) forest with a variable mixture
of hardwoods. We selected Red-cockaded Woodpecker cavities that were
not recently used by the woodpeckers and in which the resin barrier was
sufficiently degraded to allow snakes to climb to cavity entrances. Selected
cavity trees were climbed using sectional climbing ladders. The contents,
including number of Southern Flying Squirrels, were determined using a
mechanics mirror and fl ashlight. Cavities containing Southern Flying Squirrels
were used for trials. Elapsed time between climbing of tree to determine
number of squirrels and initiation of snake climbing ranged from 20–90 min.
All trials were conducted between March and August of 1991–92. Trials
were conducted during daylight hours, when temperatures were 24–30 °C.
Elaphe obsoleta of sufficient size (>105 cm total length [TL]) to easily
consume an adult fl ying squirrel were obtained opportunistically or
by trapping. Nine snakes were used in 9 independent climbing trials.
Snakes were held in the laboratory for periods up to two weeks prior to trials.
Snakes were provided with water, but not fed, during captivity. Snakes
were transported to cavity trees in cloth bags, removed from the bags, and
placed in a vertical orientation on the bole of the pine directly below the
cavity entrance. The snake’s head was initially placed approximately 2 m
above ground level. The typical response of snakes was to initiate climbing,
although it was occasionally necessary to initially steer the snake with an
aluminum pole to insure that it continued to climb vertically and remained
on the side of the bole with the cavity. Date, time, cavity height (m), entrance
diameter (mm), elapsed time to reach cavity, and outcome of the predation
event were recorded.
Nine individual E. obsoleta (TL 105–165 cm) were placed on boles of
Red-cockaded Woodpecker cavity trees, each containing a cavity known
to be occupied by 1–4 adult Southern Flying Squirrels. In all instances, the
snakes proceeded to climb to the vicinity of the cavity entrance and orient
toward the entrance. After climbing sufficiently to have an anterior segment
of the body in position, the snakes rapidly thrust the anterior portion
2009 D.C. Rudolph, R.R. Schaefer, J.B. Pierce, D. Saenz, and R.N. Conner 43
of their bodies into the cavity. This thrust into the cavity frequently elicited
vocalizations from the squirrel(s), followed by a period of relative quiescence
during which the snake ingested the squirrel. If additional squirrels
were present, this period was followed by additional movements by the
snake as it captured another squirrel. Elapsed time to climb to cavities
ranged from 7 to 38 min. In 8 of the 9 instances, the snakes were successful
in capturing at least one squirrel, and ultimately captured 14 of the 22
squirrels present in the cavities (Table 1). After all squirrels were consumed,
or escaped, the snakes completely entered the cavities, where they
presumably remained to digest their meal. Two cavities were checked the
next day and the snakes were still present.
Five of the snakes captured and consumed all squirrels (n = 1–3) present
in the cavities. If multiple squirrels were present in the cavities, the snake’s
body, approximately 50% of which remained outside the cavity, blocked the
entrance sufficiently to prevent escape of the additional squirrels. In one cavity
containing 3 squirrels, one squirrel was able to squeeze out of the cavity
past the snake’s body after considerable effort. However, the snake pinned the
squirrel to the bole of the tree using the mid-portion of its body. After consuming
the two squirrels remaining in the cavity, the snake brought the anterior
portion of its body out of the cavity and consumed the third squirrel.
In four cases, one or more of the squirrels were able to escape (Table 1).
One cavity had two entrances, and 2 squirrels escaped out the second entrance
while the snake was capturing and consuming the third squirrel. In
another instance, one of two squirrels present in a cavity with a slightly
enlarged entrance was able to escape past the snake’s body while the snake
was consuming the remaining squirrel. In a third case, the snake experienced
considerable difficulty during the final approach to the cavity entrance due
to smooth bark and the presence of resin. Consequently, its initial thrust
into the cavity was not sufficient to allow it to capture a squirrel before both
squirrels were able to escape past the snake’s head and neck. In the fourth instance,
the smallest of the 9 snakes (TL = 105 cm) totally entered the cavity,
allowing 3 of the 4 squirrels present to escape out the unblocked entrance.
Table 1. Outcomes of Elaphe obsoleta (Texas Ratsnake) predation on Glaucomys volans (Southern
Flying Squirrel) in Picoides borealis (Red-cockaded Woodpecker) cavities in eastern Texas
Snake Cavity Cavity # of #
TL height diameter G.v. predated Comments
117 9.2 47 2 2
139 5.8 46 1 1
147 6.0 46 3 3
161 8.1 50 3 3
165 7.0 49 2 2
105 6.7 51 4 1 3 escaped after snake completely entered cavity
129 6.8 43/47 3 1 2 escaped out second entrance
136 7.7 61 2 1 Cavity enlarged and 1 escaped past snake
141 7.3 45 2 0 Difficult climb and snake's initial strike ineffective
44 Southeastern Naturalist Vol. 8, Special Issue 2
In at least two cases, one or more of the squirrels detected disturbance
outside the cavity, either that of the researchers or of the climbing snake.
In both cases, a squirrel peered out of the cavity entrance and observed the
snake climbing. When the snake was within approximately 0.5 m of the cavity
entrance each squirrel retreated back into the cavity. Both were ultimately
consumed by the snakes.
Southern Flying Squirrels are abundant in southeastern US forests and
are frequent occupants of Red-cockaded Woodpecker cavities (Conner
et al. 1996, Dennis 1971, Harlow and Lennartz 1983, Loeb 1993, Rudolph
et al. 1990a). Red-cockaded Woodpeckers excavate cavities with an entrance
tube diameter of approximately 40–50 mm, and these are frequently enlarged
by secondary cavity users, especially other species of woodpeckers (Loeb
1993, Rudolph et al. 1990a). Southern Flying Squirrels prefer un-enlarged
Red-cockaded Woodpecker cavities, presumably due to the increased protection
from larger predators (Loeb 1993, Rudolph et al.1990a). However,
the preference of Southern Flying Squirrels for cavities with un-enlarged
entrances makes them vulnerable to snake predation as they are frequently
unable to exit the cavities due to the presence of the snake’s body.
These trials were artificial in the sense that the snakes did not select trees
to climb. They were initially attempting to escape from a potential predator,
the researcher, by climbing up the bole of the pine. However, at some point
they detected the presence of the cavity or squirrels, presumably using visual
and/or olfactory cues, and commenced predatory behavior. Consequently,
these data do not address search behavior of E. obsoleta, only their behavior
at the cavity.
Available data suggests that Southern Flying Squirrels do not select or
avoid cavities with an actively maintained resin barrier (Loeb 1993, Rudolph
et al. 1990a). There is some evidence that Southern Flying Squirrels seek
to avoid direct contact with the resin barrier (Schaefer and Saenz 1998);
however, they are able to land directly at the cavity entrance and thus utilize
cavities with an actively maintained resin barrier. Presumably however,
Southern Flying Squirrels have not evolved the behavioral mechanisms to
maximize the potential benefits of the presence of resin barriers in reducing
In two instances, Southern Flying Squirrels observed the approach of
the snakes from the cavity entrance, and then retreated back into the cavity.
This behavior exposes the squirrels to almost certain predation, whereas exiting
the cavity would provide almost certain escape from the approaching
snake. However, Southern Flying Squirrels exiting cavities during daylight
are potentially exposed to a variety of diurnal predators. Saenz and Schaefer
(1995) observed the capture of a Southern Flying Squirrel that they disturbed
from a cavity while they were climbing the tree, by a waiting Buteo
platypterus (Vieillot) (Broad-winged Hawk). It is also possible that Southern
2009 D.C. Rudolph, R.R. Schaefer, J.B. Pierce, D. Saenz, and R.N. Conner 45
Flying Squirrel behavior was still infl uenced by the prior disturbance due to
Ratsnakes are diurnally and nocturnally active predators with marked
arboreal tendencies. Ratsnakes frequently target Red-cockaded Woodpecker
cavities, especially during the nestling period (Neal et al. 1993). However,
based on surveys of occupants of Red-cockaded Woodpecker cavities,
Southern Flying Squirrels potentially represent a larger prey resource available
to ratsnakes than Red-cockaded Woodpecker nestlings (Harlow and
Lennartz 1983, Loeb 1993, Mitchell et al. 1999, Rudolph et al. 1990a). In
eastern Texas, surveys found that Southern Flying Squirrels, often more than
one individual, were present in 19.3 to 29.5% of Red-cockaded Woodpecker
cavities (Conner et al. 1997, Rudolph et al.1990a). In addition, Pierce et al.
(2008), also working in eastern Texas, found that Texas Ratsnake arboreal
behavior occurred throughout the active season. There was no evidence of
a peak in arboreal activity during the avian nesting season, and much of the
arboreal behavior may have been directed at non-avian prey.
The interactions between Red-cockaded Woodpeckers, Southern Flying
Squirrels, and Texas Ratsnakes are complex. Texas Ratsnakes are
efficient predators on Southern Flying Squirrels occupying Red-cockaded
Woodpecker cavities, and this fact suggests that the complex interactions
hypothesized by Kappes (2004) deserve more investigation.
We thank M.A. Kwiatkowski, R.R. Fleet, and two anonymous reviewers for
helpful comments on an earlier draft of this manuscript. S.J. Burgdorf provided field
assistance. Handling and care of animals were in accordance with ASIH Animal
Care Guidelines (see Guidelines for Use of Live Amphibians and Reptiles in Field
Research, American Society of Ichthyologists and Herpetologists at http://www.asih.
Conner, R.N., D.C. Rudolph, D. Saenz, and R.R. Schaefer. 1996. Red-cockaded Woodpecker
nesting success, forest structure, and Southern Flying Squirrels in Texas.
Wilson Bulletin 108:697−711.
Conner, R.N., D.C. Rudolph, D. Saenz, and R.R. Schaefer. 1997. Species using Redcockaded
Woodpecker cavities in eastern Texas. Bulletin of the Texas Ornithological
Conner, R.N., D.C. Rudolph, and J.R. Walters. 2001. The Red-cockaded Woodpecker:
Surviving in a Fire-maintained Ecosystem. University of Texas Press, Austin, TX.
Dennis, J.V. 1971. Species using Red-cockaded Woodpecker holes in northeastern
South Carolina. Bird-banding 42:79–87.
Harlow, R.F., and M.R. Lennartz. 1983. Interspecific competition for Red-cockaded
Woodpecker cavities during the nesting season in South Carolina. Pp. 41–43, In
D.A. Wood (Ed.). Red-cockaded Woodpecker Symposium II Proceedings. Florida
Game and Fresh Water Fish Commission, Tallahassee, FL. 112 pp.
46 Southeastern Naturalist Vol. 8, Special Issue 2
Jackson, J.A. 1974. Gray Ratsnakes versus Red-cockaded Woodpeckers: Predatorprey
adaptations. Auk 91:342–347.
Jackson, J.A. 1978. Predation by a Gray Ratsnake on Red-cockaded Woodpecker nestlings.
Kappes, J.J. 2004. Community interactions associated with Red-cockaded Woodpecker
cavities. Pp. 458–467, In R. Costa and S.J. Daniels (Eds.). Red-cockaded Woodpecker:
The Road to Recovery. Hancock House Publishers, Blaine, WA. 744 pp.
Kappes, J.J. 2008. Cavity number and use by other species as correlates of group size
in Red-cockaded Woodpeckers. Wilson Bulletin 120:181–189.
Laves, K.S., and S.C. Loeb. 1999. Effects of Southern Flying Squirrels (Glaucomys
volans) on Red-cockaded Woodpecker (Picoides borealis) reproductive success.
Animal Conservation 2:295–303.
Loeb, S.C. 1993. Use and selection of Red-cockaded Woodpecker cavities by Southern
Flying Squirrels. Journal of Wildlife Management 57:329–335.
Mitchell, L.R., L.D. Carlile, and C.R. Chandler. 1999. Effects of Southern Flying
Squirrels on nest success of Red-cockaded Woodpeckers. Journal of Wildlife
Neal, J.C., W.G. Montague, and D.A. James. 1993. Climbing by Black Ratsnakes on
cavity trees of Red-cockaded Woodpeckers. Wildlife Society Bulletin 21:160–165.
Pierce, J.B., R.R. Fleet, L. McBrayer, and D.C. Rudolph. 2008. Winter dormancy
periods and seasonal arboreal activity of the Texas Ratsnake (Elaphe obsolete) in
eastern Texas. Southeastern Naturalist 7:359–366.
Rudolph, D.C., R.N. Conner, and J. Turner. 1990a. Competition for Red-cockaded
Woodpecker roost and nest cavities: Effects of resin age and entrance diameter.
Wilson Bulletin 102:23–36.
Rudolph, D.C., H. Kyle, and R.N. Conner. 1990b. Red-cockaded Woodpeckers vs.
ratsnakes: The effectiveness of the resin barrier. Wilson Bulletin 102:14–22.
Rudolph, D.C., R.N. Conner, and J.R. Walters. 2004. Red-cockaded Woodpecker
recovery: An integrated strategy. Pp. 70–76, In R. Costa and S.J. Daniels (Eds.).
Red-cockaded Woodpecker: The Road to Recovery. Hancock House Publishers,
Blaine, WA. 744 pp.
Saenz, D, R.N. Conner, C.E. Shackelford, and D.C. Rudolph. 1998. Pileated Woodpecker
damage to Red-cockaded Woodpecker cavity trees in eastern Texas. Wilson
Saenz, D., and R.R. Schaefer. 1995. Opportunistic predation by a Broad-winged
Hawk on a Southern Flying Squirrel. Bulletin of the Texas Ornithological Society
Schaefer, R.R., and D. Saenz. 1998. Red-cockaded Woodpecker cavity-tree resin
avoidance by Southern Flying Squirrels. Wilson Bulletin 110:291–292.
Walters, J.R. 1990. The Red-cockaded Woodpecker: A “primitive” cooperative
breeder. Pp. 67–101, In P.B. Stacey and W.D. Koenig (Eds.). Cooperative Breeding
in Birds: Long-term Studies of Ecology and Behavior. Cambridge University
Press, Cambridge, UK. 615 pp.
Withgott, J.H., J.C. Neal, and W.G. Montague. 1995. A technique to deter climbing
by ratsnakes on cavity trees of Red-cockaded Woodpeckers. Pp. 294–300, In D.L.
Kulhavy, R.G. Hooper, and R. Costa (Eds.). Red-cockaded Woodpecker: Recovery,
Ecology, and Management. Center for Applied Studies in Forestry, College
of Forestry, Stephen F. Austin State University, Nacogdoches, TX. 551 pp.