Many observers have noted that breeding activity is initiated by heavy
rains in summer. In my experience precipitation of at least two inches
within a few days is necessary to bring forth large breeding choruses.
With smaller amounts of precipitation only stragglers or small
aggregations are present at the breeding ponds. Tanner (1950: 48) stated
that in three years of observation, near Lawrence, Kansas, the first
storms to bring large numbers of males to the breeding ponds occurred on
June 20, 1947, June 18, 1948, and May 1, 1949.
In 1954 the frogs were recorded first on April 25, but these were under
massive boulders, and were still semi-torpid. Frogs were found fully
active, in numbers, under small flat rocks on May 7. They were found
frequently thereafter. On the afternoon of May 13, the third consecutive
day with temperature slightly above 21 deg. C., low croaking of a frog
was heard among rocks at an old abandoned quarry. Throughout the
remainder of May, calling was heard frequently at the quarry on warm,
sunny afternoons. Often several were calling within an area of a few
square yards, answering each other and maintaining a regular sequence.
In the last week of May rains were frequent, and the precipitation
totalled 2.09 inches. On June 1 and 2 also, there were heavy rains
totalling 2.26 inches. On the evening of June 2 many frogs were calling
at a pond 1/2 mile south of the Reservation, and one was heard at the
pond on the Reservation. By the evening of June 4, dozens were calling
in shallow water along the edge of this pond in dense _Polygonum_ and
other weeds. There was sporadic calling even in daylight and there was a
great chorus each evening for the next few days, but its volume rapidly
diminished.
In mid-June a system of drift fences and funnel traps was installed 200
yards west of the pond in the dry bottom of an old diversion ditch
leading from the pond. The ditch constituted the boundary between
bottomland pasture and a wooded slope, and therefore was a natural
travelway. The object of the installation was to intercept and catch
small animals travelling along the ditch bottom. The drift fence was
W-shaped, with a funnel trap at the apex of each cone so that the
animals travelling in either direction would be caught. The numbers of
frogs caught from time to time during the summer provided information as
to their responses to weather in migrating to the pond.
TABLE 1. NUMBERS OF FROGS CAUGHT WITHIN TWO DAYS AFTER RAIN IN FUNNEL
TRAPS IN 1954, FROM MID-JUNE, TO THE TIME OF FIRST FROST.
Date Precipitation No. of
in inches caught frogs
July 1 2.02 8
July 10 .11 none
July 16 1.26 none
July 20-21 .94 3
July 24 .38 2
July 28 .29 none
August 1-2 3.22 31
August 6-7-8 2.43 none
August 12 .28 none
August 16 .29 none
August 19-22 .70 none
August 27-28 1.05 none
September 9 .50 none
September 29-30 .38 none
October 4 .74 none
October 12-14 3.51 none
From the positions of the traps and drift fences, it was obvious that
all of the frogs that were caught were travelling toward the pond.
Capture of an equal number moving away from the pond a few days
afterward might have been expected but none at all was caught while
making a return trip. Therefore it seems that the frogs returned by a
different route to their home ranges after breeding. Of necessity they
make the return trip under conditions drier than those that prevail on
the pondward trip, which is usually made in a downpour. Probably the
return travel is slower, more leisurely, and with more tendency to keep
to sheltered situations.
The call is a bleat, resembling that of a sheep, but higher, of lesser
volume, and is not unlike the loud rattling buzz of an angry bee. The
call is usually of three to four seconds duration, with an interval
several times as long. Calling males were floating, almost upright, in
the water within a few yards of shore, where there was dense vegetation.
The throat pouch when fully expanded is several times as large as the
entire head. When a person approached to within a few yards of frogs
they usually stopped calling, submerged, and swam to a place of
concealment.
Having heard the call of typical _G. carolinensis_ in Louisiana, I have
the impression that it is a little shorter, more sheeplike, and less
insectlike than that of _G. olivacea_. The call of _Gastrophryne_ is of
such peculiar quality that it is difficult to describe. Different
observers have described it in different terms. Stebbins (1951: 391) has
described the call in greatest detail, and also has quoted from the
descriptions of it previously published. These descriptions include the
following: "high, shrill buzz"; "buzz, harsh and metallic"; "like an
electric buzzer"; "like bees at close range but more like sheep at a
distance"; "bleating baa"; "shrill, long-drawn quaw quaw"; "whistled
wh[=e][=e] followed by a bleat."
Stebbins observed breeding choruses (_mazatlanensis_) at Pe[~n]a Blanca
Springs, Arizona, and stated that sometimes three or four called more or
less together, but that they seldom started simultaneously. Occasionally
many voices would be heard in unison followed by an interval of silence,
but this performance was erratic. At the pond on the Reservation I noted
this same tendency many times. After a lull the chorus would begin with
a few sporadic croaks, then four or five or even more frogs would be
calling simultaneously from an area of a few square yards. Anderson
(_op. cit._: 34) found that in small groups of calling _G. carolinensis_
there was a distinct tendency to maintain a definite pattern in the
sequence of the calls. One "dominant" individual would initiate a series
of calls, and others each in turn would take up the chorus.
Pairing takes place soon after the breeding aggregations are formed. On
the night of June 4, 1954, a clasping pair was captured and kept in the
laboratory in a large jar of water. This pair did not separate, and
spawning occurred between noon and 1:30 P. M. on June 5. When the newly
laid eggs were discovered at 1:30 P. M. most of them were in a surface
film. Some were attached to submerged leaves and a few rested on the
bottom. The pair was still joined, but the male was actually clasping
only part of the time, and as the frogs moved about in the water, it
became evident that they were adhering to each other by the areas of
skin contact, which were glued together by their dermal secretion. They
were unable to separate immediately, even when they struggled to do so.
They were observed for approximately 15 minutes before separation
occurred, and during this time they were moving about actively. As they
separated, the area of adhesion was discernible on the back of the
female. It was U-shaped, following the ridges of the ilia and the
sacrum.
On August 2, 1954, after a rain of 3.22 inches, the previously mentioned
funnel trap in the ditch had caught 31 ant-eating frogs. Water had
collected to a depth of several inches in the depression where the trap
was situated. A dozen of the trapped frogs were clasping pairs. These
frogs struggled vigorously as they were removed from the traps, handled
and marked. As a result most of the clasping males were separated from
the females. In handling those of each pair I noticed that they were
glued together by dermal secretions, as were those of the pair observed
on June 5. The areas of adhesion were of similar shape and location in
the different pairs, and included the U-shaped ridge of the female's
back and the male's belly, and the inner surfaces of the male's forelegs
with the corresponding surfaces of the female's sides where the male
clasped.
This adhesion of the members of a pair during mating may be a normal
occurrence. The copious secretion of the dermal glands is of especially
glutinous quality in _Gastrophryne_. The adhesion of members of a pair
may have survival value. These small frogs are especially shy, and in
the breeding ponds they respond to any disturbance with vigorous
attempts to escape and hide. Under such circumstances the adhesion may
prevent separation. Also, it may serve to prevent displacement of a
clasping male by a rival. Anderson (_op. cit._) who observed many
details of the mating behavior of _G. carolinensis_, both in the
laboratory and under natural conditions, mentioned no such adhesion
between members of a pair.
Anderson (_op. cit._: 31) discussed the possibility that reproductive
isolation might arise in sympatric populations, such as those of _G.
carolinensis_ in southern Louisiana, through inherent differences in
time of spawning. However, in _G. olivacea_ at least, such isolation
would be prevented by individual males returning to breed at different
times in the same season. Furthermore, individual differences in choice
of breeding time probably result from environmental factors rather than
genetic factors in most instances. In _G. olivacea_ in Kansas, time of
breeding is controlled by the distribution of heavy rainfall creating
favorable conditions. Onset of the breeding season may be hastened or
delayed, or an entire year may be missed because of summer drought. If
favorable heavy rains are well distributed throughout the summer, frogs
of age classes that are not yet sexually mature in the early part of
the breeding season, may comprise the bulk of the breeding population in
late summer.