Herpetologica, 60(4), 2004, 420–429
Ó 2004 by The Herpetologists’ League, Inc.
HOW, WHEN, AND WHERE TO PERFORM VISUAL DISPLAYS:
THE CASE OF THE AMAZONIAN FROG HYLA PARVICEPS
ADOLFO AMÉZQUITA1,3 AND WALTER HÖDL2
1
Depto. de Ciencias Biológicas, Universidad de los Andes, A.A. 4976, Bogotá, Colombia
2
Institute of Zoology, University of Vienna, Althanstraße 14, A-1090, Vienna, Austria
ABSTRACT: We performed intrusion experiments and observed the course of 13 male-male agonistic
interactions to gather information on the communicative role of visual signaling in the Amazonian tree frog
Hyla parviceps. To obtain information on the ecological context potentially associated with visual signaling, we
performed nightly censuses of calling activity and tested whether males differentially used microhabitats in
relation to properties that affect both acoustic and visual communication. Among seven behaviors performed
by males, two were visual displays. Foot-flagging displays and advertisement calls were used at a similar rate
and at similar distances between interactants. Arm-waving displays were less common and used at a closer
range than foot-flagging displays. The analysis of a dyadic transition matrix revealed that foot flagging
significantly elicited foot-flagging displays by the opponent frog. Furthermore, resident males produced more
arm wavings and calls than intruders, although the latter difference was not significant. We conclude that male
H. parviceps respond to intruders by combining advertisement calls and visual displays, and that visual signals
may serve functionally as a spacing mechanism. Comparing the properties of perches used by calling males
with a random sample of available perches indicates that males prefer perches surrounded by denser and
higher vegetation. Furthermore, calling activity occurred during or shortly after heavy rains and coincided with
calling activity of several co-occurring species of hylid frogs, which probably decreases the locatability of
calling males. We suggest that, under these conditions, the simultaneous production of auditory and visual
signals may momentarily increase a sender’s locatability when a conspecific receiver is detected.
Key words: Agonistic interactions; Anura; Communication; Habitat selection; Visual signaling
ALTHOUGH anurans are well known to use
auditory signals as the primary mode of intraspecific communication (Gerhardt, 1994;
Rand, 1988; Wells, 1977), individuals of some
species perform remarkable visual displays in
variable social contexts (Davison, 1984; Haddad and Giaretta, 1999; Harding, 1982; Lindquist and Hetherington, 1996; Richards and
James, 1992). Reviews on the use of visual
displays by anuran amphibians (Hödl and
Amézquita, 2001), reveal that all species
performing visual displays perform acoustic
displays as well, which makes it difficult to
separate the functional role of each mode of
communication. Moreover, most reports on
visual displays in anurans remain anecdotal,
and controlled experiments have been performed only recently in an attempt to elucidate
their communicative role (Lindquist and
Hetherington, 1996). Visual signaling can be
hypothesized as either an alternative or complementary communication mode in anurans,
the prevalence of which depends on the social
3
CORRESPONDENCE: e-mail, aamezqui@uniandes.edu.co
420
context and the environmental conditions under which it occurs.
Several environmental conditions may have
favored the evolution of visual displays in
anurans (Hödl and Amézquita, 2001). Breeding in noisy environments, such as near fast
streams or waterfalls, may require that acoustic signals be emphasized by visual displays
(Haddad and Giaretta, 1999; Hödl et al., 1997;
Lindquist and Hetherington, 1996). In arboreal hylids, calling from elevated perches in
dense vegetation may reduce an emitter’s
locatability (Passmore et al., 1984) or attractiveness (Penna and Solı́s, 1998) and, thus,
favor the use of complementary visual displays.
The consequences of habitat use for acoustic
communication in a single anuran species have
been discussed to some extent (Etges, 1987;
Wells and Schwartz, 1982). Visual signals,
however, differ from auditory signals in both
propagation distance and sender’s locatability
(Bradbury and Vehrencamp, 1998). Thus,
species that perform both acoustic and visual
displays may differ in the ecological correlates
of communication. An understanding of the
evolution of visual displays in anurans requires
accurate descriptions of the behaviors and
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the social context in which these acts are
performed.
The Amazonian tree frog Hyla parviceps is
considered an opportunistic breeder because
its calling activity, mainly nocturnal, seems to
be associated with occasional heavy rains
(Crump, 1974; Weygoldt, 1986). We incidentally observed males of this species extending
both arms and legs during one breeding night,
when the density of conspecific and heterospecific calling males was very high. The probability of auditory interference suggested that
H. parviceps might have aggressive or courtship visual signals redundant with acoustic
signals. The observation that males call mainly
at night and from dense vegetation suggested
that visual signals might be correlated with
environmental conditions that favor signal
propagation. Therefore, our aims in this study
are (1) to describe the visual displays of H.
parviceps as well as some ecological conditions
under which they are performed, (2) to perform intrusion experiments to obtain information about the social context associated with
visual signaling, and (3) to test whether males
differentially use microhabitats for signaling
activity.
MATERIALS AND METHODS
Study Site, Study Species, and
Breeding Activity
From 8 April–5 May of 1997, we studied
a population of H. parviceps occurring at about
150 m elevation at the Surumoni River
(Venezuela) within the Orinoco drainage (38
109 N, 658 409 W). The rainy season there
extends from April–November, with a rainfall
peak during the months of May–July (about 400
mm/mo). Annual precipitation is near 3000 mm
but year-to-year fluctuations of about 500 mm
are common. Mean annual temperature is
25.5–26.5 C, and average diurnal temperature
range (5–10 C) exceeds among-years variation
(,4 C). The vegetation at the study site consists
primarily of a relatively old, secondary growth
forest with a canopy at about 30 m.
At the study site, H. parviceps was found at
streamside ponds that were formed during
water-level rise of Surumoni river at the beginning of the rainy season. Ponds formed in this
way existed for only a few weeks before
becoming fully connected to the river. Calling
421
males, as well as amplectant pairs, of H.
parviceps were found in the vegetation above
or beside the ponds. Eggs are laid on the water
surface, and larvae probably complete their
development in a short time interval under temporal restrictions that are imposed by pond
flooding. We conducted our study with frogs
displaying from two ponds that measured 18 3
630.3 m (length3width3depth) and 12353
0.2 m. Both ponds were completely surrounded by forest. Other anuran species calling
at the site during this study included Allophryne ruthveni, Osteocephalus taurinus, Scinax sp., Hyla granosa, and Leptodactylus
knudseni.
On 37 consecutive days at the onset of the
rainy season, we performed daily censuses
of the number of calling males at the study
ponds. During this time period, water levels in
the ponds rose from ,2 cm to the level at
which they became completely flooded by the
Surumoni river. We visited ponds between
2000 h and 0100 h, walking slowly to spot all
calling males. When no calls were heard,
we waited at least 1 h at each pond before
declaring no calling activity. To test for
association between rainfall and calling activity, we used data on daily rainfall above the
forest canopy from a weather station at less
than 200 m from the furthest pond (Szarzynski, J; Surumoni-Project: Climate Monitoring,
1997; Forest-Atmosphere Interaction Research; Department of Geography, University
of Mannheim).
Behavioral Observations and
Intrusion Experiments
We observed 17 male-male interactions to
describe visual signaling behavior and the associated social context. Because most of the
spontaneous visual signals occurred during the
few hours when the density of calling individuals was highest, only 4 observations were
made of spontaneous interactions and 13 observations were of intrusion experiments. The
procedure consisted of displacing a calling
male from its perch to a new perch located at
least 50 cm from a calling male. The displaced
male was never one of the closest neighbors of
the resident (i.e., calling) male. We then
waited until one of the males either started
to call or made visual contact. Afterwards, one
of us dictated sequentially all observed behav-
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ioral patterns into a tape recorder (Fagen and
Young, 1978; Lehner, 1979). We also noted
inter-individual distances (initially expressed
in body-length units) at which behaviors were
performed. An interaction was considered terminated when one of the individuals jumped
away from the other so that visual contact was
interrupted.
In the course of inter-individual interactions,
we observed two kinds of behaviors that can be
classified as visual displays. We name them foot
flagging and arm waving, following Hödl and
Amézquita (2001). During a foot-flagging
display, a male raised one or both hind legs by
extending it/them into an arc above the substrate level. The leg was then returned to the
body side. At maximum extension, toes were
outstretched, spread, and sometimes vibrated
(Fig. 1). At maximum extension, hind legs revealed contrasting orange spots, visible only
from behind the frog. Hind legs were either simultaneously or alternatively extended. Foot
flagging was by far the most frequently
observed display during both intrusion experiments and occasional observations. In H. parviceps, arm waving consisted of lifting an arm and
waving it up and down in an arc above the head.
A maximum of five waving movements were
performed consecutively without contacting
the substrate. The movements were not performed in any recognizable temporal pattern.
Other behaviors observed during agonistic
interactions include approaching, jumping
away, turning, and uttering advertisement
calls. Approaching and jumping away are
defined according to the position of the interacting individual, i.e., approaching means
walking so that the inter-individual distance is
reduced and jumping away means jumping
(rarely walking) so that the interacting individual is left behind. Turning describes
a group of behaviors in which the observed
individual reorients the body without displacing. Turning is characterized by sequential
lifting of every foot.
Perch Use and Perch Availability
To sample the characteristics of perches
used by displaying frogs, the exact place was
marked where each calling male was located
during the census. In most cases, males that
had been momentarily displaced resumed
calling within a few minutes at a nearby perch.
[Vol. 60, No. 4
FIG. 1.—Foot-flagging male of Hyla parviceps (Hylidae)
during call interval. Photograph taken by W. Hödl at
Surumoni river near La Esmeralda, Amazonas, Venezuela.
The perch properties measured were chosen
from the literature (Arak and Eiriksson, 1992;
Etges, 1987) according to the potential value
for increasing the propagation of the signals
and for reducing locatability of senders to
potential predators. Measured properties included perch height, height of calling site
above water level; perch size, leaf area (estimated as an ellipse based on the length of the
leaf’s orthogonal axes) or branch thickness
(horizontal diameter of trunk at the place
where the frog was located); vegetation density, measured as the number of leaves that
intersect a vertical cylinder (5 cm width 3 70
cm height) centered at the frog’s location;
upper cover, as the approximate distance from
the frog to the top of the bush or tree where it
was perched; and distance to the pond edge,
expressed as positive if perches were directly
above water and as negative if they were
outside the pond. All perch variables were
measured the following day to avoid disturbing
the animals excessively. When water level rose
throughout the night, perch height and distance to pond edge were estimated, based on
marks left during the previous night.
To estimate perch availability, we measured
the same properties on all potential perches
(leaves as well as branches) intersecting vertical
planes of two transect lines per pond. The
azimuth direction of the first transect plane at
each pond was randomly chosen; the second
plane was orthogonal to it (in order to reduce
the potential effect of environmental gradients). Transect planes extended up to 2 m
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423
To test whether visual displays were significantly preceded by any other behavior, we
performed binomial tests between observed
and expected behavioral transitions (Baker and
Gillingham, 1983; Bels and Crama, 1994).
To test whether perches are selected
according to the properties we measured, we
compared each property between used and
available perches with a Kolmogorov-Smirnov
test. Since the null hypothesis is that no
selection of perches occurs, we used a Bonferroni procedure to adjust significance levels
for the number of variables tested (Scheiner,
1993).
FIG. 2.—Observed (open circles) occurrence of calling
activity by males of Hyla parviceps in a given night as
a function of daily rainfall. Data were collected during 37
consecutive days at the beginning of the rainy season at
Surumoni river near La Esmeralda, Amazonas, Venezuela.
Filled circles denote the corresponding expected probabilities according to a logistic regression model.
outside the pond edge, which represents the
maximum distance at which a calling frog was
detected.
Statistical analyses
To compare the prevalence of behaviors,
the inter-individual distance at which they
were performed, and their frequency in relation to the status of the individual at the
beginning (resident versus intruder) and at the
end (winner versus loser) of the interaction, we
used the experimentally induced behavioral
interactions as the statistical units of analysis
(i.e., we calculated one value of each variable
for each behavioral interaction). Nonparametric analyses were used because of nonnormal
distribution of data.
To analyze behavioral transitions within the
same subset of data, behavioral sequences
were displayed in the form of a first-order
contingency table. Rows represent preceding
behaviors and columns represent succeeding
behaviors that were performed by another
individual (Fagen and Young, 1978). Given the
prevalence of low frequency values within the
cells, a randomization test was used to evaluate
the independence between rows and columns.
RESULTS
Calling and breeding activities are opportunistic in H. parviceps. Most breeding activity
occurred between 0–2 d of a heavy rainfall. We
used daily rainfall and daily temperature
(minimum, average, maximum) as predictor
variables of presence (1) or absence (0) of
nightly calling activity in a logistic regression
model. Only daily rainfall was a significant predictor of calling activity (Log likelihood if term
removed 5 19.13, P 5 0.001, n 5 31 d; P .
0.354 for other variables), and calling activity
most probably occurred when rainfall exceeded
30 mm/d (Fig. 2).
In the course of 13 male–male behavioral
interactions, we observed 309 behaviors performed by 27 different males. Sixty-seven of
these acts (21.7%) were foot-flagging displays,
and 18 (5.8%) were arm-waving displays. Foot
flagging was performed in 9 and arm waving in
8 of 13 male-male interactions. Within a single
interaction, foot-flagging displays were as common as acoustic signals (Fig. 3), whereas armwaving displays were less common than
acoustic signals.
When Are Visual Displays Performed?
To know whether visual displays are preferentially performed when males approach
each other beyond a threshold distance, we
compared the inter-individual distance at
which behaviors were performed. For each
single interaction, we calculated the minimum,
median, and maximum distance at which each
category of behavior was performed. Footflagging distance (average minimum average
maximum; 8–21 cm) was slightly shorter than
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[Vol. 60, No. 4
FIG. 4.—Minimum (left extreme), median (filled circle),
and maximum (right extreme) distance between opponents
at which visual displays (arm waving and foot flagging) and
other behaviors are performed in the course of agonistic
interactions between males of Hyla parviceps (n 5 13
behavioral interactions).
FIG. 3.—Number of occurrences of visual displays (arm
waving and foot flagging) compared to other behaviors
performed by males of Hyla parviceps (Hylidae) in the
course of agonistic interactions. Bars indicate median
values, upper and lower end of the boxes denote upper and
lower quartiles; open circles represent outliers and points
represent extremes from each distribution (n 5 13
behavioral interactions).
calling distance (15–26 cm). Arm waving was
performed at shorter distances (11–13 cm)
than calling (Fig. 4).
Resident males performed more arm-waving displays (Fig. 5a; Wilcoxon signed ranks
test; Z 5 2.23, P 5 0.026; n 5 13
interactions) and tended to produce more calls
(Z 5 1.75, P 5 0.081; n 5 13 interactions)
than intruders. There was no difference in the
number of arm-waving displays between males
that remained at the calling perches at the end
of the interactions (winning males) and fleeing
(losing) males (Fig. 5a; Wilcoxon signed ranks
test; Z 5 0.21, P 5 0.832; n 5 13
interactions). Likewise, the number of foot
flagging displays did not differ between
resident and intruder (Fig. 5a; Wilcoxon
signed ranks test; Z 5 0.85, P 5 0.397; n 5
13 interactions), and between winner and loser
(Fig. 5a; Wilcoxon signed ranks test; Z 5
1.19, P 5 0.236; n 5 13 interactions) males.
The first-order sequential analysis on a dyadic matrix (Table 1) revealed that the
probability of one individual performing a be-
havior was associated with the preceding act
performed by another individual (Monte Carlo
Test on a 7 3 7 contingency table: number of
trials 5 100,000, P 5 0.0013 6 0.0001, n 5
161 transitions). To know the potential role of
any behavior in eliciting a visual display, we
performed binomial tests between those behavioral transitions that presented the largest
differences between observed and expected
frequencies according to the dyadic matrix
(Baker and Gillingham, 1983; Bels and Crama,
1994). We corrected the significance levels for
the tests performed using a sequential Bonferroni adjustment (Scheiner, 1993). Footflagging displays were significantly preceded
by foot flagging of the interacting individual
(Binomial randomization test; one-tailed P 5
0.0001, critical P-value 5 0.0500) and turning
movements were significantly preceded by
turning movements of the interacting individual (Binomial randomization test; one-tailed
P 5 0.0046, critical P-value 5 0.0250).
Otherwise, calling tended to follow approaching (Binomial randomization test; one-tailed
test P 5 0.0302, critical P-value 5 0.0125); and
approaching tended to follow moving away
(Binomial randomization test; one-tailed test
P 5 0.0201, critical P-value 5 0.0063). Arm
waving was not significantly preceded by any
behavior (one-tailed test P . 0.1769 in all
cases).
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425
Where Are Visual Displays Performed?
Male H. parviceps differentially used
perches in relation to vegetation density and
cover height (Fig. 6). More males were found
at perches that were surrounded by dense
vegetation (Kolmogorov-Smirnov test; Z 5
3.30, P , 0.001) and that were part of high
trees (Z 5 2.75, P , 0.001). Males, however,
did not differentially use perches in relation to
their height (Z 5 1.15, P 5 0.141), their
distance to pond edge (Z 5 0.73, P 5 0.670),
their area (for leaf perches; Z 5 1.31, P 5
0.066), or their thickness (for branch perches;
Z 5 1.00, P 5 0.273).
DISCUSSION
In the course of male-male agonistic interactions in H. parviceps, visual signals are at
least as frequently used as acoustic signals.
Both types of signals were observed in most
interactions and were produced at similar rates
during a single interaction. The extensive use
of visual signals suggests that they are functional components of the communication
system and poses interesting questions about
their communicative role and the evolutionary
scenario under which they evolved. Below we
discuss our results from two perspectives: (1)
the probable communicative role of the visual
signals and (2) the possible ecological correlates of the visual signaling in H. parviceps.
FIG. 5.—Number of occurrences of visual displays (arm
waving and foot flagging) and other behaviors performed
by males of Hyla parviceps in the course of agonistic
interactions. Occurrences are separated according to the
status of the individual at the beginning (A; white: resident,
oblique lines: intruder) and at the end (B; white: winner,
oblique lines: loser) of each trial. Bars indicate median
values; upper and lower end of the boxes denote upper and
lower quartiles; open circles represent outliers and points
represent extreme values from each distribution. See text
for details of the statistical analyses (n 5 13 behavioral
interactions).
The Communicative Role of Visual Signals
Social interactions have favored the evolution of 2–3 across-species categories of signals
in anurans (Bogert, 1960; Duellman and Trueb,
1986; Kluge, 1981; Rand, 1988): advertisement
calls, aggressive/territorial calls, and, in some
species, courtship calls. Spontaneous (i.e., in
the absence of other individuals) performance
of visual signals has been reported for some
anuran species that evolved visual communication (Hödl et al., 1997; Pavan et al., 2001),
suggesting a communicative role comparable to
the role of advertisement calls: to indicate
a male’s reproductive disposition to potential
receivers of either sex (Grafe, 1995; Harrison
and Littlejohn, 1985; Ryan and Rand, 1998;
Schwartz and Wells, 1985). We believe, however, that visual signaling in H. parviceps does
not serve advertisement purposes, because we
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HERPETOLOGICA
[Vol. 60, No. 4
TABLE 1.—Dyadic matrix summing up behavioral transitions during male-male agonistic interactions in the Amazonian
tree frog Hyla parviceps. Asterisks denote behavioral transitions that occurred at frequencies higher than expected
according to binomial tests. See text for details of analyses.
Successive behavioral unit
Approach
Arm waving
Assault
Call
Foot flagging
Move away
Turn
Total
Count
Expected count
Count
Expected count
Count
Expected count
Count
Expected count
Count
Expected count
Count
Expected count
Count
Expected count
Count
Expected count
Approach
Arm waving
Assault
Call
Foot flagging
Move away
Turn
Total
5.0
3.6
1.0
0.4
0.0
1.4
7.0
5.4
0.0
3.1
7.0
3.1
3.0
5.4
23.0
23.0
1.0
1.1
0.0
0.1
0.0
0.4
0.0
1.7
1.0
1.1
2.0
1.0
3.0
1.7
7.0
7.0
1.0
0.9
0.0
0.1
0.0
0.4
3.0
1.4
1.0
0.9
1.0
0.8
0.0
1.4
6.0
6.0
9.0
4.7
0.0
0.6
3.0
1.9
7.0
7.1
5.0
4.7
1.0
4.1
5.0
7.1
33.0
33.0
2.0
4.8
0.0
0.6
3.0
1.9
8.0
7.3
**12.0**
4.8
3.0
4.2
3.0
7.3
31.0
31.0
3.0
4.0
1.0
0.5
4.0
1.6
4.0
6.1
3.0
4.0
3.0
3.6
8.0
6.1
26.0
26.0
4.0
5.9
1.0
0.7
0.0
2.4
9.0
9.0
3.0
5.9
5.0
5.2
**16.0**
9.0
38.0
38.0
25.0
25.0
3.0
3.0
10.0
10.0
38.0
38.0
25.0
25.0
22.0
22.0
38.0
38.0
161.0
161.0
never observed visual displays performed by
individuals that were not approached by
a second male. There is still a good possibility
that visual displays play a role as courtship
signals that allow, for example, sex recognition
between males and females (Rand, 1988; Wells,
1977; Zimmermann and Zimmermann, 1988).
In addition to the male-male interactions
described in this paper, we observed two
male-female encounters that involved 21
behaviors, six of them consisting of arm-waving
displays that were performed by a single male in
one of the interactions. This interaction did not
lead to amplexus and oviposition.
From our data, the functional role of visual
signals in H. parviceps can be compared to the
role of aggressive calls. Because males in
almost all intrusion experiments performed
some kind of visual displays, we interpret arm
waving and foot flagging as behaviors that
signal aggressive motivational states. Furthermore, foot flagging significantly elicited foot
flagging by interacting males. Advertisement
calls were also produced after the intrusion of
a second male, but we did not find any evidence
of a distinctive aggressive call in H. parviceps.
Instead, most males responded to intruders by
combining advertisement calls and visual displays, suggesting that visual signals may function as aggressive calls (mediating spacing) in
other species.
Most visual displays occurred at interindividual distances below 30 cm, which may
be partly attributed to an experimental artifact,
i.e., experimental observations were initiated
by placing a male within 50 cm of a focal male.
However, during both registered and nonregistered spontaneous interactions that involved visual displays, we always estimated
inter-individual distances shorter than 50 cm.
In other anuran species (Grafe, 1995;
Schwartz and Wells, 1985; Wells and
Schwartz, 1984), focal males produced more,
more complex, or longer aggressive calls when
experimental stimuli simulated one individual
excessively approaching the calling male. In
this study, resident males tended to perform
more arm waving (significant differences) and
to call more (nonsignificant differences) than
intruders (Fig. 5). In our opinion, the sum of
our results strongly suggests that visual signals
play a role in the evolution of agonistic
interactions.
Ecological Correlates of Visual Signaling
In another study, we have explored several
hypotheses about ecological correlates for the
evolution of visual communication: diurnality,
aposematism, signaling from acoustically complex environments, and signaling from noisy
environments (Hödl and Amézquita, 2001).
December 2004]
HERPETOLOGICA
FIG. 6.—Features of perches used by males of Hyla
parviceps to call and perform visual displays (oblique lines)
as compared with features of available (white) perches (see
text for sampling procedure). Asterisks denote perch
features in which used perches differed from available
perches at P , 0.008 (after Bonferroni’s correction). Bars
indicate median values, upper and lower end of the boxes
denote upper and lower quartiles, and open circles
represent outliers from each distribution.
The repertoire of visual signals is relatively low
in H. parviceps, which agrees with previous
predictions on the relative importance of
diurnality in the evolution of anuran visual
communication. Whereas the frog species
exhibiting the largest repertoires of visual
displays are diurnal, H. parviceps is primarily
nocturnal and only occasionally extends its
breeding activity to the first hours of the
daytime. Furthermore, the coloration pattern
of H. parviceps in the resting position does not
seem to contrast against natural backgrounds.
We, therefore, discuss below the possible
importance of visual signaling for communication in environments where the locatability of
sender is reduced.
427
Calling males were disproportionally found
at perches with high vegetation density. From
the acoustic point of view, this result is
unexpected since sound propagation may be
diminished under these conditions (Ellinger
and Hödl, 2003; Penna and Solı́s, 1998;
Richards and Wiley, 1980). One can speculate
that perches within dense vegetation reduce
locatability of senders to aerial predators such
as bats. Calling male Physalaemus pustulosus
(Ryan, 1985; Tuttle and Ryan, 1981) and
Smilisca sila (Da Silva Nunes, 1988) change
their behavior in the presence of bats. Indeed,
during the course of this study, we observed
bats preying upon frogs such as Osteocephalus
taurinus that were calling from elevated
perches. In spite of the potential benefits as
antipredator strategy, calling from relatively
hidden perches reduces the locatability of
males to potential conspecific receivers, which
could in turn reduce mating opportunities or
increase the costs (time, energy, predation
risk) of repelling other males. Under this
scenario, the simultaneous production of
auditory and visual signals may momentarily
increase a sender’s locatability when a conspecific receiver is detected. Moreover, calling
activity of males of H. parviceps is strongly
associated with heavy rains (this study; Crump,
1974; Weygoldt, 1986), when the cacophony
produced by other breeding species may
negatively affect acoustic communication
(Narins and Zelick, 1988; Schwartz and Wells,
1983). Visual signaling may thus favor species
recognition in species breeding within large
assemblages, when acoustic and visual environments become too complex. These hypotheses deserve further testing by comparing, for
example, phylogenetically close species that
vary in signal stereotipicity, signal repertoire,
and microhabitat used for displaying.
Acknowledgments.—This research was funded by the
Austrian Science Foundation (FWF) grant to W. Hödl (P
11565-Bio). We thank I. Strausz for invaluable field assistance and personal support; B. Rojas, V. Flechas, and L.
Castellanos for help in data organization; and J. Szarzynski
and N. Ellinger for providing data on the local weather.
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Accepted: 3 June 2004
Associate Editor: Edmond Brodie
Herpetologica, 60(4), 2004, 429–437
Ó 2004 by The Herpetologists’ League, Inc.
A REPATRIATION STUDY OF THE EASTERN MASSASAUGA
(SISTRURUS CATENATUS CATENATUS) IN WISCONSIN
RICHARD KING1,4, CRAIG BERG2,
AND
BOB HAY3
1
Necedah National Wildlife Refuge, Necedah, WI 54646, USA
2
Milwaukee County Zoo, Milwaukee, WI 53226, USA
3
Wisconsin Department of Natural Resources, Madison, WI 53703, USA
The use of relocations, repatriations, and translocations as amphibian and reptile conservation strategies has
received much debate. In the case of endangered species, their use may outweigh the potential negative
consequences. We performed an experimental repatriation of the eastern massasauga (Sistrurus catenatus
catenatus), which has experienced range-wide population declines and extirpations. The experiment included
measures to minimize negative conspecific effects to the donor populations as well as inter-species effects on
the release and donor sites. Snakes released during late July had lower mortality rates, larger home ranges, and
gained more mass than snakes released in early September. The July release cohort also successfully
reproduced, while no breeding activity was observed with September release snakes. Results of this study
suggest that repatriation may be a viable method of restoring eastern massasauga populations. We hope the
methods and conservation measures used in this experiment will serve as a template for future repatriations.
Key words: ecology; recovery; repatriation; Sistrurus; snakes
ALTHOUGH herpetologists undoubtedly have
been conducting transplants for decades, only
recently has the efficacy of transplanting or
repatriating individuals received rigorous debate (Burke, 1991; Dodd and Seigel, 1991;
Grifith et al., 1989; Plummer and Mills, 2000;
Reinert, 1991; Sealy, 1997). Ultimately, the
need for repatriation (Dodd and Seigel, 1991)
involves balancing two opposing issues: (1) the
need to recover a species, which often includes
expanding populations into formerly occupied
habitats and (2) the obligation to do no harm
to the individuals being released as well as
resident animals.
4
CORRESPONDENCE: e-mail, richard_s_king@fws.gov
The purpose of this study was development
of an ethical repatriation method for a species
that clearly warrants it, the eastern massasauga
(Sistrurus catenatus catenatus), in the hope
that it will serve as a template for future repatriations. We chose a study design that minimizes impacts on the founder and resident
snake populations. To achieve this, the study
sites had to meet the following criteria: (1) sites
had to be void of eastern massasaugas, which
by definition eliminated any impacts on
resident massasaugas; (2) the sites had to have
harbored eastern massasaugas in the past,
which demonstrates the sites’ ability to harbor
massasaugas if habitat conditions are right; and
(3) the cause of extirpation, in this case habitat
degradation, must have been reversed prior to
the study (Dodd and Seigel, 1991).