The gluttonous king: the effects of prey size and repeated feeding on predatory performance in kingsnakes

Abstract

Constriction is an evolutionarily and functionally important behavior that many snakes use to subdue a variety of prey. However, little work has examined the effects of prey size on constriction performance. Furthermore, many snakes are known to feed even while previously consumed prey remain in the stomach. This temporary increase in mass may place constraints on subsequent performance. To test these effects, I investigated constriction performance in eastern kingsnakes Lampropeltis getula handling different sizes and quantities of rodent prey in two experiments by measuring coil length and peak constriction pressure. In the first experiment, constriction coil length and peak constriction pressure did not differ significantly between snakes feeding on either ‘small’ (5% relative prey mass, RPM) or ‘large’ (15% RPM) rodent prey. However, there was a significant interaction between prey size and repeated feeding. Snakes that had previously consumed large meals had significantly shorter coil lengths and lower peak constriction pressures when fed for a second time (reductions of 60 and 51%, respectively). In Experiment 2, snakes offered five sequential, similarly sized prey (@ 7% RPM), showed a regular decrease in coil length and peak constriction pressure across sequential feeding trials. During the final (fifth) trials, snakes used 45.7% shorter coils and exerted 50.1% lower peak constriction pressures. Thus, prey size alone did not affect constriction performance, but predation performance was significantly affected by the prior consumption of prey ≥7% RPM, and performance was further reduced during additional feeding trials.

Full text

The gluttonous king: the effects of prey size and repeated
feeding on predatory performance in kingsnakes
D. A. Penning
1,2
1 Department of Biology and Environmental Health, Missouri Southern State University, Joplin, MO, USA
2 Department of Biology, University of Louisiana at Lafayette, Lafayette, LA, USA
Keywords
constriction; constriction performance;
constriction pressure; feeding; Lampropeltis;
predation; snakes; prey size.
Correspondence
David A. Penning, Department of Biology and
Environmental Health, Missouri Southern State
University, Joplin, MO 64801, USA.
Email: davidapenning@gmail.com
Editor: Mark-Oliver R€
odel
Received 27 July 2016; revised 30 November
2016; accepted 1 December 2016
doi:10.1111/jzo.12437
Abstract
Constriction is an evolutionarily and functionally important behavior that many
snakes use to subdue a variety of prey. However, little work has examined the
effects of prey size on constriction performance. Furthermore, many snakes are
known to feed even while previously consumed prey remain in the stomach. This
temporary increase in mass may place constraints on subsequent performance. To
test these effects, I investigated constriction performance in eastern kingsnakes
Lampropeltis getula handling different sizes and quantities of rodent prey in two
experiments by measuring coil length and peak constriction pressure. In the first
experiment, constriction coil length and peak constriction pressure did not differ
significantly between snakes feeding on either ‘small’(5% relative prey mass,
RPM) or ‘large’(15% RPM) rodent prey. However, there was a significant interac-
tion between prey size and repeated feeding. Snakes that had previously consumed
large meals had significantly shorter coil lengths and lower peak constriction pres-
sures when fed for a second time (reductions of 60 and 51%, respectively). In
Experiment 2, snakes offered five sequential, similarly sized prey (@ 7% RPM),
showed a regular decrease in coil length and peak constriction pressure across
sequential feeding trials. During the final (fifth) trials, snakes used 45.7% shorter
coils and exerted 50.1% lower peak constriction pressures. Thus, prey size alone
did not affect constriction performance, but predation performance was significantly
affected by the prior consumption of prey ≥7% RPM, and performance was further
reduced during additional feeding trials.
Introduction
Both predators and prey have morphological, physiological,
and behavioral mechanisms for increasing their predation or
escape success (Darwin, 1859; Dawkins & Krebs, 1979; Herrel
& Gibb, 2006). However, these mechanisms are subject to
trade-offs (Zera & Harshman, 2001; Ings & Chittka, 2008) and
constraints (Wainwright, 1988; Undheim et al., 2015). For
example, increased cranial kinesis in snakes allowed for the
ingestion of large prey (Gans, 1961), while likely reducing bite
force (Frazzetta, 1970; Greene, 1983; Penning, 2016). There-
fore, snakes required additional means to subdue large prey
such as constriction or venom (Greene, 1997; Cundall &
Greene, 2000; Lillywhite, 2014). Constriction is a behavioral
pattern that immobilizes prey with two or more points on the
snake’s body (Greene & Burghardt, 1978), typically involving
fully encircling body loops around the prey (Mehta, 2003;
Moon & Mehta, 2007; Penning, Dartez & Moon, 2015). Con-
striction behavior is a key innovation in the evolution and radi-
ation of snakes (Greene & Burghardt, 1978; Lillywhite, 2014),
is integral to their feeding biology (Moon, 2000), and is
therefore an evolutionarily and functionally important predation
mechanism (Greene & Burghardt, 1978; Penning & Dartez,
2016).
Many constricting snakes feed on a wide range of prey sizes
(relative prey mass [RPM] range =0.004–1.36; Greene, 1997;
King, 2002; Rodr
ıguez-Robles, 2002; Jackson, Kley & Brain-
erd, 2004) and are known to modify their prey-handling behav-
iors in response to different prey sizes and activity levels (de
Queiroz, 1984; Mehta, 2003). For example, smaller prey are
often seized and eaten alive (de Queiroz, 1984; Mehta, 2003,
2009), without the use of constriction. It is possible that some
prey are so small that a snake could not form an effective coil
around it. However, to my knowledge, the functional limita-
tions of constriction on small prey have not been tested. Con-
striction is an energetically expensive behavior (Canjani et al.,
2003; Penning & Dartez, 2016) and snakes can modulate their
efforts in response to prey cues (Moon, 2000; Boback et al.,
2012), so seizing and eating small prey alive likely reduces the
energy demands on the snake without high risks of injury from
small prey. While smaller prey may be eaten alive, larger and
more active prey are typically constricted (de Queiroz, 1984;
Journal of Zoology  (2016) – ª2016 The Zoological Society of London 1
Journal of Zoology. Print ISSN 0952-8369

Mehta, 2003, 2009; Penning & Cairns, 2016). It is currently
hypothesized that larger prey may require more strength to
subdue (Moon, 2000), and require more of the body to be
used during constriction (Hisaw & Gloyd, 1926). Moreover,
larger prey may be less susceptible to being subdued by con-
striction mechanisms (Hardy, 1994). Relatively large prey are
presumed to be less susceptible to cardiovascular interference
during constriction (Hardy, 1994), but this hypothesis has yet
to be tested.
In addition to variations in prey size, snakes can encounter
variations in prey quantity. Both terrestrial (Hisaw & Gloyd,
1926; Taylor, 2001; Clark, 2002; Rodr
ıguez-Robles, 2002) and
aquatic snakes (Lillywhite, 2014) are known to consume multi-
ple prey in a single feeding. Feeding may have a large and
immediate impact on body mass (Cundall & Greene, 2000;
Jackson et al., 2004). Added body mass can leave a snake
more vulnerable to predators by potentially reducing predator
evasion (Shine, 1980; Mehta, 2006), sprint speed (Ford &
Shuttlesworth, 1986; Mehta, 2006), endurance (Ford & Shut-
tlesworth, 1986; Herzog & Bailey, 1987), and can also alter
antipredator displays (Herzog & Bailey, 1987; Mehta, 2006).
In addition to these consequences, the presence of extra mass
in a snake’s digestive tract is likely to affect subsequent preda-
tion performance. The previously ingested food may cause
changes in mobility and possibly interfere with, and limit, axial
bending. Limitations in axial bending would likely reduce con-
striction performance because the coil could not properly form.
A snake that cannot form a tight coil cannot effectively trans-
fer the contractile forces from their axial muscles to the surface
area of the prey inside a circumferential coil. Despite the wide
range of relative prey sizes taken by constricting snakes, and
the importance of constriction in the evolution of snakes
(Greene & Burghardt, 1978; Greene, 1983), investigations on
the effects of prey size, and repeated prey encounters on con-
striction performance are lacking. I conducted two experiments
using eastern kingsnakes Lampropeltis getula. Experiment 1
combined the effects of prey size, repeated feeding, and their
interaction on constriction performance. Experiment 2 was an
experimental test based on field observations of snakes that
had fed on multiple prey items (Hisaw & Gloyd, 1926; Cun-
ningham, 1959; Lillywhite, 2014) and quantified the effects of
five sequential feeding trials of similarly sized prey on con-
striction performance.
Materials and methods
In Experiments 1 and 2, each snake was housed individually
and was provided water ad libitum, with light provided on a
12:12-h cycle. All enclosures were clear or semi-opaque
plastic enclosures measuring either 45 930 916 cm or
55 939 913 cm with recycled paper substrate. Snakes were
fasted for 2 weeks before trials, but were otherwise fed pre-
killed rodents weekly. Snakes were purchased from private
breeders.
For Experiment 1 (see below), I used 20 kingsnakes (L. getula;
mass =240.3 46.7 g [mean SE], mass range =102–810 g;
snout-vent length [SVL] =76.2 5.0 cm, SVL range =
50.4–120.4 cm). Maximum body diameters (the primary
predictor of constriction performance; Moon & Mehta, 2007;
Penning et al., 2015; Penning & Dartez, 2016) varied by less
than 2 cm. All snakes were at least 2 years old and the sample
consisted largely of one sex (19 females, 1 male). Data from the
male fell within the data collected from the entire sample. Experi-
ment 1 tested the effects of prey size, repeated feeding, and their
interaction on constriction performance. I randomly divided the
20 snakes into two groups and assigned them to either the ‘small’
prey category (5% relative prey mass, RPM) or the ‘large’prey
category (15% RPM). Body mass was not significantly different
between the two groups of snakes (t
18
=0.12, P>0.9). I offered
each snake its first prey item (pre-killed Mus musculus or Rattus
norvegicus purchased frozen from a commercial supplier) with an
attached pressure sensor (0.5 or 2.0 ml, fluid-filled bulb) con-
nected to a digital pressure transducer (Harvard Apparatus Pres-
sure Transducer, Model 60-3002). Prey of an appropriate RPM
were chosen for each snake, depending on their body mass, and
ranged from juvenile mice to juvenile rats (small
RMP =12.5 2.5 g; large RPM =34.9 6.4 g). I attached
the sensor to the prey with wax-coated string. Upon presentation,
all snakes readily struck at and constricted the prey. During con-
striction, I systematically shook the prey with forceps to elicit
maximum constriction effort (Moon, 2000; Penning & Dartez,
2016) for 5 min (body twitches at @ 10-s intervals). I recorded
the peak constriction pressure exerted on the prey. All snakes
experienced similar simulated prey struggling. I did not record
the durations of feeding bouts because the simulated prey move-
ments directly affected the prey-handling durations. When prey
struggling stopped, all snakes responded by downregulating their
pressure exertion and began ingestion. Once exertion began to
decline (indicated by a gradual drop in pressure), I marked the
beginning and end of the constriction coil with small pieces of
tape (in order to measure coil length).
Previous work has measured coil size by counting the num-
ber of loops used in a coil (Moon & Mehta, 2007; Penning
et al., 2015; Penning & Dartez, 2016). Using loop number
allows for the quantification of constriction coil size without
the unwanted variation caused by snake body size. For exam-
ple, both a hatchling and giant snake can use three loops in a
coil even though the absolute coil length would vary consider-
ably. Loop number is independent of body size and can be
incorporated into models with other size-dependent variables
without the issue of multicollinearity between predictor vari-
ables. Previous research using loop number as a quantification
of coil size has investigated constriction performance of snakes
varying by orders of magnitude in size (Moon & Mehta, 2007;
Penning et al., 2015; Penning & Dartez, 2016). Here, the east-
ern kingsnakes are similar in size, so I measured coil length
instead of loop number.
After marking the coil length, I clipped the string that held
the pressure sensor to the prey and pulled the sensor out of
the coil. When the snake loosened its coil and straightened its
body, I took an overhead photo with a scale grid in view. I
measured coil lengths using the program ImageJ (Schneider,
Rasband & Eliceiri, 2012). Immediately after the first feeding
trial, I offered each snake a second prey item (of the same
approximate mass as the first one) and repeated the procedure
described above. There was no rest period between repeated
2Journal of Zoology  (2016) – ª2016 The Zoological Society of London
Constriction performance in kingsnakes D. A. Penning

prey encounters. Because I had to physically handle snakes to
remove the sensor (and disturb their feeding), I did not mea-
sure the duration of the ingestion period.
For Experiment 2, I used 10 medium-sized, female east-
ern kingsnakes L. getula (mass =123.4 7.8 g, mass
range =105.3–171.4 g; SVL =64.0 1.7 cm, SVL range =
57.1–73.9 cm). I used snakes and mice of specific sizes to
measure changes in constriction performance during a preda-
tory event. If a wild snake finds a mammal nest, it will likely
feed on multiple prey; documented cases of 1–35 rodents
within a snake’s stomach have been reported previously (Pack,
1919; Hisaw & Gloyd, 1926; Cunningham, 1959; Rodr
ıguez-
Robles, 2002). I sequentially presented each snake with six
mice of a size that would naturally be found in nesting groups
(6.1–11.5 g; Schwartz & Schwartz, 1981). Each meal was
approximately 7% RPM (range =5.7–8.9%). Based on average
prey length (snout–tail base) and average snake length (SVL),
each prey spanned @ 9% of each snake’s SVL. I controlled
prey mass to within 1 g for each snake across all sequential
trials, and later confirmed that there was no significant differ-
ence in prey mass across trials (grand mean =8.6 0.25 g;
range =6.1–11.5 g; F
4,6
=1.4, P>0.26). For every sequential
prey item, I recorded coil length and maximum constriction
pressure following the methods described for Experiment 1.
Statistical analyses
I log-transformed all data for all models. For Experiment 1, I
used a repeated measures ANOVA (multivariate approach;
Vasey & Thayer, 1987). For each dependent variable (coil
length and peak constriction pressure), I treated the feeding tri-
als (1st or 2nd) as the repeated measures independent variable.
Prey size was treated as the between-subjects independent vari-
able. I also tested for a significant interaction between the two
independent variables. If an interaction between factors was
significant, I reported Tukey’spost hoc tests for simple main
effects (Nieuwenhuis, Forstmann & Wagenmakers, 2011) with
P-values based on the studentized range statistic (Hammer,
Harper & Ryan, 2001). For Experiment 2, I used a one-way
repeated measures ANOVA for each dependent variable, with
feeding trial (first through fifth) as the repeated measure. If the
main effect was significant, I reported Tukey’spost hoc tests
between each pair of feeding trials. I used Past (version 3.08;
Hammer et al., 2001) and JMP Pro (version 11.00.0; Statistical
Analysis System, Cary, NC, USA) software for analyses and
considered the results significant at P<0.05.
Results
For Experiment 1, all snakes constricted and consumed both
prey items, showing no signs of reduced interest during the
second feeding trial. The kingsnakes quickly struck at and con-
stricted their prey using 1–3 loops in their coils, resulting in
coil lengths of 10.7–84.2 cm and peak constriction pressures
of 6.5–32.7 kPa (kilopascals). There was a significant interac-
tion effect between prey size (5 and 15% RPM) and repeated
feeding trials (1st and 2nd prey) on coil length used
(F
1,18
=4.6, P<0.047; Fig. 1a). During the first feeding trial,
there was no significant difference in coil length between the
two prey-size groups (Tukey’sq=0.53, P>0.98). Addition-
ally, for snakes feeding on smaller prey, there was no signifi-
cant difference between coil lengths used during the first
(45.7 7.2 cm) and second (32.9 3.9 cm) feeding trials
(q=3.0, P>0.17). However, for snakes feeding on large
prey, there was a significant difference between the coil
lengths used during the first (46.6 7.3 cm) and second
(18.6 2.8 cm) feeding trials (q=10.13, P<0.001; Figs 1a
and 2). In most feeding events involving a second large prey
item, new constriction coils stopped where a prey bulge was
visible (Fig. 2). This large reduction in coil length is the cause
of the significant interaction between prey size and repeated
prey encounters.
Peak constriction pressures followed the same pattern as coil
lengths (Fig. 1) in Experiment 1. There was a significant inter-
action effect between prey size and repeated feedings on peak
constriction pressure (F
1,18
=18.1, P<0.001; Fig. 1b). On the
first feeding, there was no significant difference in peak con-
striction pressure between the two prey-size groups (Tukey’s
q=1.15, P>0.84) or between the first (23.7 1.8 kPa) and
Figure 1 Coil length (a) and peak constriction pressures (b) for first
and second feeding trials on large and small prey by Lampropeltis
getula. Bars and lines indicate means SE. Different letters above
bars denote pairwise significant differences based on Tukey’s post
hoc tests.
Journal of Zoology  (2016) – ª2016 The Zoological Society of London 3
D. A. Penning Constriction performance in kingsnakes

second (18.42 1.1 kPa) feeding trials involving small prey
(q=3.72, P>0.06). However, for snakes feeding on large
prey, there was a significant difference between the peak con-
striction pressures during the first (22.5 2.3 kPa) and second
(11.0 1.1 kPa) feeding trials (q=10.82, P<0.001). The
peak constriction pressures used by snakes constricting their
second large meal were significantly lower than those used in
both the first (q=11.97, P<0.001) and second (q=8.25,
P<0.001) feeding trials involving small prey. Similar to the
results for coil length used, the significant reduction in peak
constriction pressure by snakes feeding on large prey for the
second time is the cause of the significant interaction between
prey size and repeated prey encounters.
For Experiment 2, all snakes constricted and consumed only
five prey items. Across the five sequential feeding trials,
snakes showed signs of reduced interest in prey and no snake
accepted the sixth prey item when offered. Coil length was
significantly different across the five sequential feeding trials
(F
4,6
=16.0, P<0.01; Fig. 3a), with more of the body being
used in the first feeding trial (29.9 3.1 cm) compared to all
others (all post hoc comparisons P<0.05). Coil length was
also significantly shorter in feeding trials four (17.4 1.6 cm;
q=4.06, P<0.048) and five (14.7 1.2 cm; q=6.43,
P<0.001) compared to the second feeding trial
(22.3 1.8 cm). Coil lengths used in feeding trials three, four,
and five were not significantly different from one another (all
P>0.05). During the third feeding trial, snakes used 35%
shorter coils compared to the first trial and during their fifth
trial, they used less than half their initial coil lengths (49.2%).
Repeated feeding trials affected peak constriction pressure in
the same manner as coil length. Peak constriction pressure was
significantly different across five sequential feeding trials
(F
4,6
=19.8, P<0.01; Fig. 3b), with pressures being highest
during the first feeding trial (24.7 2.3 kPa) compared to all
others (all post hoc comparisons P<0.05). Peak constriction
pressure was also significantly lower in feeding trials four
(12.5 1.5 kPa; q=4.27, P<0.036) and five
(13.4 1.5 kPa; q=4.25, P<0.037) compared to the second
feeding trial (17.5 1.9 kPa). Peak constriction pressures in
feeding trials three, four, and five were not significantly differ-
ent from one another (all P>0.05). By feeding trial three,
snakes were exerting 36% lower peak constriction pressures
compared to their first prey, and during their fifth feeding trial,
peak constriction pressure was reduced by 46% compared to
their initial performance.
In Experiments 1 and 2, most of the body loops were char-
acterized by the snake’s ventral region, rather than the dorsum,
facing the head (Fig. 2). Regardless of the coil posture, many
of the trials involved high peak constriction pressures. In
Experiment 1, peak constriction pressures were similar to those
shown to cause circulatory arrest in rodents (20.8 kPa; Boback
Figure 2 ALampropeltis getula (eastern kingsnake, 198 g) constricting
its first (a) and second (b) mouse (15% relative prey mass each). Peak
constriction pressure during the first trial was 30.9 kPa with a coil
length of 63.9 cm. During the second trial, peak pressure was 13.3 kPa
with a coil length of 23.5 cm; the coil stopped at the portion of the body
where the previous prey was contained within the stomach. [Color
figure can be viewed at wileyonlinelibrary.com]
Figure 3 Coil length (a) and peak constriction pressure (b) for 10
Lampropeltis getula constricting mice during five sequential feeding
trials (@ 7% RPM). Bars and lines indicate means SE. Letters
above bars denote pairwise significant differences based on Tukey’s
post hoc tests.
4Journal of Zoology  (2016) – ª2016 The Zoological Society of London
Constriction performance in kingsnakes D. A. Penning

et al., 2015) for snakes handling their first (23.7 1.8 kPa,
1-sample t
9
=1.62, P>0.13) and second (18.4 1.1 kPa,
t
9
=2.0, P>0.06) small prey, as well as for snakes handling
their first large prey (22.5 2.3 kPa, t
9
=0.72, P>0.47). In
Experiment 2, kingsnakes exerted similarly high pressures dur-
ing the first two sequential prey encounters (24.0 2.2 kPa,
t
9
=1.5, P>0.17; 17.4 1.7 kPa, t
9
=2.0, P>0.08, respec-
tively), but constriction performance steadily dropped thereafter
(Fig. 3).
Discussion
Constriction is a key behavioral innovation in the evolution of
snakes (Greene & Burghardt, 1978) that may be affected by
aspects of prey size and repeated prey encounters. The results
of these experiments are some of the first quantitative tests of
several assumptions of predator–prey dynamics involving con-
stricting snakes, variations in prey size, and repeated encoun-
ters with prey.
Almost a century has passed since Hisaw & Gloyd (1926)
stated that constricting snakes increase the size of the coil in
proportion to prey size. Subsequent work has not addressed
this observation, or has been unable to systematically control
relative prey size (Moon & Mehta, 2007; Penning et al., 2015;
Penning & Dartez, 2016). In contrast to the statement of
Hisaw & Gloyd (1926), kingsnakes used similar coil lengths
on both small and large prey. Previous work has shown that
the number of loops used in a coil (e.g., coil size) may (Moon
& Mehta, 2007) or may not (Penning et al., 2015; Penning &
Dartez, 2016) affect peak constriction performance in a variety
of snakes (mainly pythons). Kingsnakes in both of my experi-
ments showed the same patterns of variation in both coil
length and peak constriction pressure. Constriction events
involving significantly shorter coils had significantly lower
peak constriction pressures (Figs 1 and 3). For kingsnakes,
using more of the body in a constriction coil results in higher
peak constriction pressure.
When snakes fed on a second large prey item (Experiment
1), they showed decreases in predation performance. Snakes
are likely experiencing fatigue during sequential feeding trials.
However, for Experiment 1, fatigue was likely not the cause of
the reduced performance in snakes feeding on large prey over
two feeding trials. In Experiment 1, the only difference
between feeding trials was prey size. Prey struggling and con-
striction duration were constant across trials (because snakes
only constricted as long as the prey continued to struggle). If
fatigue from constriction behavior was playing a role in Exper-
iment 1, it should have affected snakes feeding on small and
large prey similarly. In Experiment 1, the only reduction in
maximum constriction pressure came from snakes using shorter
coils (the second large prey trial). When coils remained similar
in length, constriction pressures were similar (both small prey
trials), suggesting that fatigue did not contribute significantly
to the reduction in constriction pressures used during the sec-
ond, large prey trial. However, to better assess the potential
importance of fatigue, future experiments should vary the rest-
ing length between meals and account for the potential differ-
ences in energy required to ingest prey of different sizes.
Snakes in Experiment 2 constricted five sequential prey
items and showed a steady decrease in constriction perfor-
mance across trials. However, based on my experimental
design, I am unable to separate the effects of fatigue from
sequential feeding trials. Future experiments could test for the
effects of fatigue by implanting prey within each snake’s stom-
ach and test for a reduction in performance without the snakes
having to exert any energy prior to the feeding event of inter-
est. Those results could then be compared to the data presented
here.
Reductions in mobility likely played an important role in
snakes with reduced constriction performance. The previously
ingested prey may physically constrain axial flexion, coil
length, and peak constriction pressure. Prey are somewhat
compliant and malleable, but their presence within a snake’s
stomach probably makes movement more difficult. In most
cases, the constriction coil stopped where a prey bulge was
visible (Fig. 2) and sequentially adding new prey to the stom-
ach increased the length of body that was not being used dur-
ing subsequent constriction events. This constraint on coil
length led to significant decreases in peak constriction pressure
and the performance patterns were similar between coil length
and peak constriction pressure in both experiments.
Relative prey mass is known to affect aspects of prey han-
dling (Mehta, 2003, 2009) and the way the coil is applied/
formed in snakes (Greenwald, 1978; Moon, 2000). Moon &
Mehta (2007) stated that constriction performance was also
likely to vary with relative prey size. Furthermore, Hardy
(1994) stated that relative prey size may play an important role
in determining the proximate mechanism of death during con-
striction, with larger prey being killed by suffocation rather
than circulatory arrest. However, on the first encounter with
prey, kingsnakes exerted similar pressures on both small and
large prey, regardless of RPM (Fig. 1b). These pressures were
similar to the pressures shown to cause rapid incapacitation via
circulatory arrest on prey of much larger absolute size
(@ 400 g Rattus rattus; Boback et al., 2015).
When variation in prey size was coupled with the effects of
repeated feeding, subsequent constriction performance was
greatly reduced. The peak constriction pressures for several tri-
als were significantly lower than those shown to cause rapid
incapacitation via circulatory arrest (Boback et al., 2015).
However, the lowest constriction pressures (mean
range =11.0–15.36 kPa) were similar to the arterial blood
pressure of rodents (10.0–16.7 kPa; Turney & Lockwood,
1986), and circulatory arrest can be caused by pressures high
enough to interfere with venous blood flow (Moon & Mehta,
2007; Boback et al., 2015), which is much lower than arterial
blood pressure (Hardy, 1994; Moon, 2000). Therefore, while
constriction performance was reduced, these reduced constric-
tion pressures are likely still high enough to significantly
impair circulatory function by stopping venous return (Moon,
2000; Moon & Mehta, 2007; Boback et al., 2015).
Acknowledgments
I thank M. Fulbright, I. Moberly, B. Moon, M. Perkins, and L.
Jones for their helpful discussions and support. I also thank J.
Journal of Zoology  (2016) – ª2016 The Zoological Society of London 5
D. A. Penning Constriction performance in kingsnakes

Albert, A. Herrel, P. Leberg, B. Moon, and D. Povinelli and
two anonymous reviewers for providing comments on earlier
drafts that helped improve the quality of the paper. I thank
BhB Reptiles, the Kansas Herpetological Society, the Louisiana
Board of Regents (Doctoral Fellowship), and the National Geo-
graphic Society (Grant 7933-05 to Brad Moon) for partial
funding. This work was also made possible by the Herpetolo-
gists’League Graduate Research Award.
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D. A. Penning Constriction performance in kingsnakes

Graphical Abstract
The contents of this page will be used as part of the graphical abstract of html only. It will not be
published as part of main article.
Many snakes are known to feed on a variety of different sizes and quantities of prey. Successful predation may place constraints
on subsequent predation performance. Using eastern kingsnakes Lampropeltis getula, I show that prey size alone does not affect
constriction performance, but snakes show reductions in predation performance when feeding on multiple prey of ≥7% relative prey
mass.