Calls of all five taxa were compared in several characteristics, of
which three are deemed most significant systematically. These are
1) the pattern and duration of the notes of a call-group, 2) the
fundamental frequency, and 3) the dominant frequency. Air temperatures
were noted at the time the calls were recorded, but no valid
correlation could be determined between this factor and any of the
parameters of the calls; consequently recordings made at all
temperatures (21-29 deg. C.) were grouped together.
_Pattern and duration of notes._--In all five taxa the basic pattern
consists of a call-group made up of one primary note followed by a
series of shorter secondary notes. In some species the secondary notes
differ from the primary in other characteristics. Both subspecies of
_Hyla microcephala_ have a long, unpaired primary note followed by 0
to 18 (usually about 4) somewhat shorter paired secondary notes. In
calls of _Hyla m. microcephala_ the mean duration of the primary is
0.131 (0.10-0.16) second and that of the secondaries is 0.101
(0.05-0.14) second, whereas in _H. m. underwoodi_ the mean duration of
the primary is 0.018 (0.05-0.15) second and that of the secondaries is
0.086 (0.06-0.11) second.
_Hyla robertmertensi_ has a reverse of this pattern in that the primary
note is paired and the secondaries are unpaired. In the sample studied
a call-group contains 0-28 secondary notes (generally about 3). The
mean duration of the primary is 0.091 (0.07-0.11) second and that of
the secondaries is 0.040 (0.025-0.06) second.
_Hyla phlebodes_ and _sartori_ have call-groups composed of a rather
short, unpaired primary and several short, unpaired secondaries
(0-28 in _phlebodes_, 0-23 in _sartori_). The mean duration of the
primary of _phlebodes_ is 0.105 (0.07-0.16) second and that of the
secondaries is 0.067 (0.035-0.12) second. The mean duration of the
primary of _sartori_ is 0.080 (0.07-0.09) second and that of the
secondaries is 0.053 (0.035-0.07) second.
The two subspecies of _H. microcephala_ are identical in call pattern
and agree closely in duration of notes, although those of the nominate
subspecies tend to be slightly longer. _Hyla robertmertensi_ is
distinctive in call pattern in that it is the only species having a
paired primary; the duration of the primary is completely overlapped by
that in the other species, but the secondaries tend to be the shortest
in the group. The call patterns of _H. phlebodes_ and _H. sartori_ are
identical and the range of duration of notes of _phlebodes_ completely
overlaps that of _sartori_, although both the primary and secondary
notes of the latter tend to be somewhat shorter (Table 5, Pl. 16).
_Fundamental frequency._--This parameter was analyzed for the primary
notes. It was measured for the secondaries as well and was found to
differ in magnitude in the same way as the primary note. In a few
examples of both subspecies of _H. microcephala_ a high primary note,
in which the fundamental frequency is exceptionally high, is sometimes
emitted (Fouquette, 1960b). None of these notes was used in this
analysis; only the fundamental frequencies of normal primary notes are
compared (Table 5, Fig. 7).
Table 5.--Comparison of Normal Mating Calls in the Hyla microcephala
Group. (Observed Range Given in Parentheses Below Mean;
Unless Otherwise Noted Data Are for Primary Notes.).
----------------+--+---------+---------+-------------------+--------------
| |Dominant | Funda- |Duration of notes | Repetition
| | | mental| (seconds) | rate of
Species |N |frequency|frequency+---------+---------+ secondaries
| | (cps) | (cps) | Primary |Secondary|(notes/minute)
----------------+--+---------+---------+---------+---------+--------------
_H. m. |44| 5637 | 205 | 0.13 | 0.10 | 268
microcephala_ | |(5150 |(184-244)|(0.11 |(0.05 | (192-353)
| | -5962)| | -0.16)| -0.14)|
| | | | | |
_H. m. |47| 5772 | 220 | 0.11 | 0.09 | 283
underwoodi_ | |(5177 |(192-275)|(0.05 |(0.06 | (197-384)
| | -6200)| | -0.15)| -0.11)|
| | | | | |
_H. |25| 5388 | 162 | 0.09 | 0.04 | 418
robertmertensi_| |(5150 |(140-178)|(0.07 |(0.03 | (368-570)
| | -5785)| | -0.11)| -0.06)|
| | | | | |
_H. phlebodes_ |34| 3578 | 148 | 0.11 | 0.07 | 284
| |(3220 |(125-158)|(0.07 |(0.04 | (210-350)
| | -4067)| | -0.16)| -0.12)|
| | | | | |
_H. sartori_ |10| 3217 | 126 | 0.08 | 0.05 | 434
| |(2950 |(116-135)|(0.07 |(0.04 | (396-477)
| | -3600)| | -0.09)| -0.07)|
----------------+--+---------+---------+---------+---------+--------------
The two subspecies of _H. microcephala_ agree closely in fundamental
frequency. There is considerable overlap, but the difference
between the means is significant at the 0.001 level of probability
(t = 4.2406). The call of _H. robertmertensi_ does not overlap that
of _H. sartori_ or either subspecies of _H. microcephala_ in this
parameter; but it does overlap that of _H. phlebodes_, although again
the difference between the means is significant at the 0.001 level
(t = 9.360). _Hyla phlebodes_ and _sartori_ have the lowest fundamental
frequencies, and there is some overlap, but here too the difference
between the means is significant at the 0.001 level (t = 4.923).
_Dominant frequency._--A dominant band of frequencies cuts across
the harmonics of the fundamental, obscuring the harmonic pattern and
generally shifting upward in frequency. The midpoint of this band is
measured at the terminal border as the dominant frequency. As with the
fundamental frequency, only the normal primary notes were utilized in
the comparisons (Table 5, Fig 8).
[Illustration: Fig. 7. Variation in the fundamental frequency of the
normal primary notes in the _Hyla microcephala_ group. The
horizontal lines = range of variation, vertical lines = mean,
solid bars = twice the standard error of the mean, and open
bars = one standard deviation. The number of specimens in each
sample is indicated in parentheses after the name of the taxon.]
The two subspecies of _H. microcephala_ agree more closely in this
parameter than in fundamental frequency. The overlap is great, but the
difference between the means is significant at the 0.001 level
(t = 3.658). The calls of both subspecies completely overlap that of
_robertmertensi_ in this parameter, but the difference between the
means is significant at the 0.001 level. The calls of _H. phlebodes_
and _H. sartori_ overlap considerably in this characteristic, although
the difference between the means is significant at the 0.001 level
(t = 7.504) (Fig. 9). The call of neither species overlaps those of
_H. microcephala_ and _robertmertensi_.
[Illustration: Fig. 8. Variation in the mid-point of the dominant
frequency band of the normal primary notes in the _Hyla
microcephala_ group. The horizontal lines = range of variation,
vertical lines = mean, solid bars = twice the standard error of
the mean, and open bars = one standard deviation. The number of
specimens in each sample is indicated in parentheses after the
name of the taxon.]
[Illustration: Fig. 9. Scatter diagram relating the dominant and
fundamental frequencies of the normal primary notes in the
_Hyla microcephala_ group. Each symbol represents a different
individual.]
_Repetition rate._--The repetition rate of the secondary notes, in
calls consisting of more than one secondary, was measured for each
form. A considerable amount of variation in this parameter was found
in all of the taxa (Table 5). This variation probably is due in part
to the effect of temperature differences. Repetition rate is the only
parameter analyzed for which there is a correlation with the
air-temperature, but even here the correlation is weak, probably due
to the microenvironmental effects of humidity, air-movement, and other
factors in addition to the ambient air temperature that influences the
body temperature of the frogs. These rates are nearly alike in both
subspecies of _H. microcephala_ and in _phlebodes_. The repetition
rates in _H. robertmertensi_ and _H. sartori_ are considerably faster
than in the other three taxa. _Hyla sartori_ has the fastest
repetition rate of the group.
In all characteristics of the mating calls the two subspecies of
_H. microcephala_ agree closely, as might be expected, although the
differences are statistically significant. _Hyla robertmertensi_ is
distinctive in call pattern and seems to be closer to _microcephala_
in dominant frequency but closer to _H. phlebodes_ in fundamental
frequency. Thus, it is somewhat intermediate between _microcephala_
and _phlebodes_. The identical pattern and similarity in fundamental
and dominant frequencies of the calls of _H. phlebodes_ and _H. sartori_
possibly indicate close relationship.
_Geographic variation in call._--_Hyla m. microcephala_ has higher
fundamental and dominant frequencies in Costa Rica than in Panama. In
Costa Rican _H. m. underwoodi_ the fundamental and dominant frequencies
are lower than in other parts of the range. Frogs of this subspecies
recorded in Nicaragua and Honduras have slightly lower dominant
frequencies and higher fundamental frequencies than those recorded in
Guatemala or Oaxaca. The duration of both primary and secondary notes
decreases to the south; samples from Nicaragua and Costa Rica have the
shortest notes. Comparison of duration of notes in the two subspecies
shows that the Panamanian _H. m. microcephala_ have slightly longer
notes than do any _H. m. underwoodi_; the more northern populations of
_H. m. underwoodi_ from Mexico most closely approach _H. m.
microcephala_ in this characteristic.
The calls of _H. robertmertensi_ in Oaxaca have higher dominant and
fundamental frequencies and longer secondary notes than do those in
Chiapas.
The calls of _H. phlebodes_ recorded at Puerto Viejo, Costa Rica,
have slightly lower dominant frequencies than do those recorded at
Turrialba, Costa Rica, and in Panama, whereas those recorded at
Turrialba have lower fundamental frequencies than in other samples.
The duration of notes is slightly shorter in both Costa Rican samples
than in those recorded in Panama.