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Pup's broadband vocalizations and maternal behavior in the rat
Behavioural Processes, 33 (1995) 257-272 0 1995 Elsevier Science B.V. All rights reserved 0376-6357/95/$09.50
BEPROC
257
00563
Pup’s broadband vocalizations and maternal behavior in the rat Richard Ihnat, Nicholas Department
of Biological
R. White and Ronald J. Barfield *
Sciences, Busch Campus,
Rutgers University,
Box 1059,
Piscata way NJ, 08855- 1059, USA
(Accepted
25 March
1994)
Abstract
Rat pups emit broadband the ultrasonic under
which
the calls are emitted,
female’s
behavior.
different
ways.
the horizontal Vocalizations into contact
vocalizations
range. Three experiments
undertaken
extending
Broadband plane.
calling
and the effects that they
when
occurred
In a second study, the mother
occurred
most often when
might
was observed engaged
moving
while
have on the maternal in several
up and moved
interacting
in behaviors
that brought
Key words:
to reduce
Contact;
rough handling
Maternal
behavior;
or inadvertent
contact
Pup; Broadband
her In
to controls, deafened only if the female was
during the first of two tests, when the pups were two days old. Broadband
may function
off
with her litter.
in the nest, and pup licking.
temporarily deafened. Relative contact with the pups, although
to
the circumstances
by the experimenter
the pup was picked
the mother
with the pups, such as nest entry,
from the audible
to determine
In the first study, pups were manipulated
another experiment, females were females engaged in more incidental deafened
with components were
calling
by the mother.
vocalization
Introduction Ultrasonic
vocalizations
are employed
ubiquitously
by rodents
during
social
behavior
such as sex and aggression (Barfield et al., 1979; Nyby and Whitney, 1977, Sales, 1972a,b; Sales and Pye, 1974). Rodent pups of a variety of species produce calls, often in the
* Corresponding author. SSDI 0376-6357(94)00028-F
258
ultrasonic
range,
but sometimes
Sales and Smith, associated
with
1978).
in the range audible
Two patterns
isolation
of calling
and the other with
One pup call, a pure tone of 40-50 rats and mice when Sales and when
Zippelius
the pups are developing
and Banks, 1971; Okon,
maternal
Schleidt,
homeothermy
1971;
and 4-65
and cold (Noirot,
and Oswalt
(Sales and Pye, 1974; extensively
1968;
1956).
ms duration
Oswalt
Maximal
occur in 1975;
and Meier,
ultrasonic
and are most susceptible
and Meier,
in rats, one
handling.
kHz in frequency
pups are isolated
Pye, 1974;
to humans
have been studied
calling
occurs
to cold stress (Allin
1975).
When rat pups are handled, they emit both audible and ultrasonic calls (Noirot, 1971; Okon, 1972). The audible calls were similar in structure to the broadband calls described below.
Okon
between both
(1972) and after
audibly
when
picked
up
characterized
levels
a broadband
Okon
mother
of the
‘wriggling’
bands
had frequencies
IO kHz with
behavior
Haack et al. (1983)
reported
few ultrasonic
when
components,
in response
to handling pups called
mouse
and
came
(rolled
Bernecker
unmodulated
into contact
and changing
harmoni-
with
the pup.
Another
pups pushed for mothers’
was at
associated
position
calls. One call, with handling.
over, (1986)
Most of the energy
These calls were
nest-building
when
Ehret
aged
that
numerous
components. broadband
in pups
by the experimenter
0.5 and 4 kHz.
rough maternal
occurred
emitted
recently,
the mother
between licking,
with
handled
More
in evidence
also observed
call in mice with
two similar
up to 80 kHz was associated
most
calls were
and
no ultrasonic
that included
were
(1970)
neck).
sweeps that was emitted
below
maternal
by the
scruff
ultrasounds
days; audible
this period.
retrieved
by the
cally related
that
days and 14-16
4-5
before
The lowest
observed
with
on the nest.
bands extending
broadband nipples
call, with or struggled
in the nest. Elwood and McCauley (1983) reported a broadband pups containing a low band of about 1 kHz in frequency reached
the ultrasonic
these broadband similar
range.
Elwood
vocalizations
during
aversive
maternal
contact.
by pups of other
species,
including
mice. The mouse
calls emitted
had components The current reliably elicited
in the ultrasonic
behavior.
A further
of the mother
Broadband
suggest that rat pups generally These authors
experiment
emit
describe
call, however,
range.
study was undertaken to determine whether broadband from rat pups and whether they occurred in conjunction
deafening
Experiment
and McCauley
‘audible call’ from 6-day-old rat with several harmonics that rarely
was performed
on maternal
to determine
calls could be with maternal
the effects
of temporary
behavior.
1 vocalizations
were tape recorded
tally. In addition, pups were handled calls could be elicited reliably.
from rat pups and analyzed
in specific
ways to determine
spectrographi-
whether
broadband
Subjects Eighteen pups were drawn from the litters of three Long-Evans female rats. About two weeks after their arrival in the laboratory, each female was inseminated by a vigorous stud male. Until the final week of pregnancy, females were individually housed in the rat colony. They were then transferred to 48 x 25 X 30 cm glass aquaria in a separate room. Each mother remained in her aquarium with her litter until the end of the experiment.
259 Food, water and nesting materials on a reverse
were continually
12 : 12 light cycle with
available.
lights out at IO:00
The animals were maintained
h.
Apparatus Pups were tested in a 68 X 32 X 32 cm polyethylene monitored
through
converts
ultrasounds
Vocalizations located
35
recorded
over
the
pass filter,
center
equipment
spectrographically
receiver
tub.
The
Kjaer 4135
Hz and 100 ktiz.
cm)
per second
had a flat response analyzed
with
detector’),
condenser
mic:rophone,
to a Bruel and Kjaer 2160 measuring
(76.2
vocalizations
(‘bat
were which
range.
a Bruel and
of the
tub. Ultrasonic
heterodyne
audible
through
set to 2000
at 30 inches
recording
a QMC
into the humanly
was coupled
band
running
with
were
cm
preamplifier, 3550
earphones
which
amplifier
A Lockheed
and
tape
recorder
the vocalizations.
to at least 100 kHz. Taped Sonagraph
in
and a Krone-Hite
Store-4
was used to record
a Kay Digital
microphone
has a built
All
vocalizations
a Uniscan
were
II continuous
sound spectrograph. Design Each pup was tested once only, There were
either
9 pups in each age group:
litters. Each pup was given 4 handling pick up, back and forth preliminary
on day 2, 5 or 10 (the day of birth was day 0).
3 pups were treatments
and rotation,
drawn
in a random
randomly
from each of the 3
order:
based on the procedures
no handling
of Okon
(control),
(1972)
and our
observations.
Procedure Pups were undisturbed interval ink,
removed
of about
so that
recorded
from
for 5 min
the
litter
would
not
taken
to a testing
Each test lasted
3 min. After testing,
they
and
acclimatization.
pups returned
be tested
again.
room.
pup was gently
to the litter,
Vocalizations
left
by an
after being marked
from
the
with
pups were
tape
test, pups were simply
left on the floor of the tub. In the ‘pick up’ test, the
lifted 3 cm from the floor of the tub by the nape of the neck and put down
at the end of the 15-s interval.
In the ‘back and forth’
condition,
the pups were
3 cm from the floor of the tub by the nape of the neck and moved on
a horizontal
movement
plane
for
a distance
of 10 cm.
were made over the 15-s test period.
lifted between was rotated
two fingers by the nape of the neck and rotated
A spectrograph
of a typical
pup audible
5 to
7 back
condition,
picked
up
back and and
forth
the pups were
to an angle of 45”. The pup
call is shown
in Fig. 2. For statistical to an analysis
purposes,
of variance.
on Fig. 1. It contains
from 2 to 64 kHz, thus with components
The mean number of ultrasonic and broadband subjected
About
In the ‘rotation’
rhythmically
5 to 7 times in each test.
slightly modulated sweeps extending sonic and ultrasonic ranges. shown
were
in all tests.
In the control
forth
They
15 s, and was separated
all data
a series of in both the
calls in each age and test condition were
Post hoc orthoganal
transformed contrasts
logarithmically were
performed
is and as
TIME IN MSEC
Fig. 1. Sound spectrograph
of a typical
BROADBAND
pup broadband
call.
PUP VOCALIZATIONS
DAY 2
IJ
CONTROL
E
PICK UP
q
BACK AND FORTH
DAY 10
DAY 5 DAY OF TESTING
ULTRASONIC
PUP VOCALIZATIONS
DAY 2
DAY 5
DAY 10
DAY OF TESTING
Fig. 2. Frequency
of occurrence
of audible
handling
broadband
condition
r
calls and
ultrasonic
and at each age level.
vocalizations
in each
261 necessary.
There
was
a reliable
x test
handling
interaction
for
both
ultrasonic
calling
(F(6,70) = 7.27; P < 0.001) and broadband calling (F(6,70) = 23.48; P < 0.001). On day 2, ultrasonic calls occurred much more often in the control condition any other condition
(F(1,70)
= 49.34;
P < 0.001).
At age 5 days, there were
than
in
no significant
differences across handling conditions (F(1,70)= 2.59; NS). On day 10, pups emitted more ultrasonic calls in the rotation condition than in any other condition (F(1,70)= 5.11; P<
0.05). Broadband
(F(1,69)
calling
day
calling
was higher
broadband
generally
2 = 229.74;
when the pup was rotated
occurred
day
5 = 148.60;
P’s < 0.001).
on day 2 than day 5 (F(1,69)
calls were
negatively
correlated
= 17.00;
with
on test days 2 and 5
During
rotation,
P < 0.001).
ultrasonic
broadband
The occurrence
calls (r(l05)
= -0.32;
of P <
0.001).
In general, reported Bernecker range
the vocalizations
by Elwood (1986) ultrasonic
!&day-old
bands.
components
pups. Broadband
day 5 or the characteristics Broadband
whether Noirot
up
and
the broadband (1972)
Okon
occurred
(1972)
5 and ultrasonic consistent
structurally
and McCauley
from 6 day old pups, whereas
similar
calls may contain
fewer
ultrasonic
to those
and Ehret and
reports on the upper
reported
broadband
calls
we taped
calls from 2- and
frequency
components
after
of the call may differ across strains.
calls can be reliably
picked
were
in rats and Haack et al. (1983)
In rats, Elwood
elicited
up by the nape of the neck and rotated; merely
in this study
(1983)
in mice. In both rats and mice, there are conflicting
of the harmonic
without
recorded
and McCauley
moved
from pups aged 2 and 5 days old when
horizontally.
These
calls reported
by Elwood
when
mothers
rodent
noted that audible calls occurred
with those of Okon,
picked
it does not occur if the pup is left undisturbed observations
and McCauley
moved
calls occurred
their
raise the
question
(19831, Okon
of
(1972) and
pups off the horizontal
in response to handling
or
plane.
prior to day 4 or
at a later age. The results of the present study are relatively in that broadband
calls occur at higher levels on day 2 than
on day 5, and not at all on day 10. Our that
results are not entirely
only
broadband
broadband
calls occur
ultrasounds handling.
are emitted,
Experiment A detailed tions occur
consistent
calls are elicited in response whereas
with
Elwood
by handling,
to handling.
on day 10, only
On
and McCauley’s
(1983)
not
ultrasounds.
day
5, both
ultrasounds
On
suggestion day
broadband
are emitted
2, only calls and
in response
to
2 ethological in relation
analysis was undertaken to maternal
behavior
to determine
when
broadband
vocaliza-
patterns.
Subjects Thirteen experiment.
females
were
mated
and
On the first day, postpartum
maintained
in the
litters were culled
manner
described
to 10 pups.
in the
first
262
Apparatus Mothers
and litters were
the tape recording a 20 channel
observed
equipment
in their
home
aquaria.
was not used; instead,
Esterline Angus event
Unlike
behavioral
the first experiment,
events were recorded
with
recorder.
Design and procedure At least 2 h prior to testing, the aquarium an adjoining
testing room.
and litter was observed ‘control’
condition,
for three
5-min
third control
the mother
was maintained
for 15 min under three conditions.
the nest was left undisturbed
periods,
separated
during
by an interval
and litter was moved
the nest material
During
the first observation,
observation.
for 15 min without
interruption.
from
and the pups were
the aquarium
(‘scatter’
condition).
returned
to the aquarium,
interruption.
After
another
condition). 15 min
scattered
evenly
The nest was also moderately and the mother
Testing occurred
Fifteen
min after the
the pups within
the
The litter was then observed
break,
the mother
over the floor
disturbed.
and litter
the
Litters were observed
of IO to 15 min.
(the ‘disturb’
to
at 22°C _t 2°C. Each female
test, the nest was stirred up with a long metal rod, moving
nest and disturbing
Behavior
containing
Room temperature
The female
were
observed
was removed
of the aquarium was immediately
for 15 min without
when the pups were 2 days old (day of birth is day 0).
recorded
Retrieval:
The female
picks up a pup in her mouth
Licking:
The mother
licks the pup. Licking was often accompanied
Nest Building:
lation of the pup. The female transports nesting material
material
around
The female
licks or cleans herself.
Eating:
The female
chews food,
Locomotion:
The female engaging
by manipuor pushes
her nose or paws.
feces or nesting material.
or adjusts
in any other
it to the nest.
into the nest in her mouth,
the nest with
Grooming:
moves
and returns
her body
behavior
pattern
position. described
If the female
was
in this list, locomo-
tion was not scored. The
Immobility:
female
movements.
was
motionless,
While
the pups and appeared immobility behavior
observed
Emission of broadband
Vocalization:
purely
ultrasonic
for
breathing
or
frequently
minor
head
crouched
over
to be nursing. As in the case with ‘locomotion’,
was not scored pattern
except
in the nest, the female if the female
was engaging
in any other
in this study.
vocalizations
vocalizations
by the pups. The occurrence
of
was not recorded.
Results Statistical
analysis revealed
of the control observation
condition;
no significant
difference
thus the results were
totalled
between
the 3 observation
and treated
as a single
periods 15min
period.
Frequencies of each behavior pattern are shown on Table 1. An analysis of variance (ANOVA) was performed for each behavioral measure; the F and P values are reported in Table 1. When appropriate, individual post hoc tests (orthogonal comparisons) were
263 TABLE 1 Mean
frequency
Experiment
of occurrence
of behavior
patterns
by the mother
and pups in each condition
Disturbance
condition
Control
P<
F
Scatter
Disturb
Move
39.72
(3.08)
31.36
(I ,431
33.54
(1.41)
Remain still
34.91
(4.13)
18.64
(2.74)
10.91
(I .85)
26.01
0.001
Retrieve
0.09
(0.18)
1.82
(0.57)
10.45
(0.72)
71.63
0.001
Lick pups
6.91
(1.98)
4.73
(1.58)
3.09
(0.90)
0.27
Nest-building
2.91
(I .28)
10.82
(2.35)
13.00
Eat
0.45
(0.24)
0.73
(0.38)
0.64
(0.31)
Enter nest
2.82
(0.04)
5.27
(0.96)
10.64
(0.70)
28.45
0.001
Exit nest
1.82
(0.51)
5.36
(0.97)
10.64
(0.68)
40.79
0.001
8.18
(1.27)
5.91
79.55 (15.75)
80.91
Self-groom Broadband
calls
4.27
(1.51)
87.00
(16.33)
are
in the text.
performed
and
performed
on the data prior to analysis.
reported
There were fewer to the control
the scatter O.OOl>,
incidences
condition
and disturb
and
= 10.62;
conditions
less likely
to be immobile
0.001
0.16
(I .I 2)
1.81 0.07
a logarithmic
transformation
and scatter conditions
NS). Mothers
than in the control
0.05
11.58
(11.20)
No difference
= 0.59;
3.75
(I .54)
in the disturb
P < 0.01).
(F(1,20)
condition again
If necessary,
of locomotion
(F(1,20)
in the disturb
immobile
of
error in parentheses)
3 (standard
condition
in the scatter
was detected were
relative between
less likely
(F(1,20)
condition
was
to be P <
= 16.41;
(F(1,20)
= 10.33;
P < 0.01). Retrieval, small
but
(F(1,20)
as might
be expected,
significant
= 4.35;
conditions
increase
P < 0.05).
(F(1,20)
increased
in retrieval
when
the pups were scattered.
between
the
There was a large difference
= 83.99;
Finally,
the
female
was more
likely
relative to the control
nest = 12.98;
P < 0.01).
condition
(F(1,20)
Location
of mother
Two-day-old broadband be expected broadband
enter
pups
calling when
generally
the mother were
(F(1,20)
= 26.53;
Correlations
between
broadband
whether
both
to enter
conditions
the disturb
and scatter
enter
increase
in both
measures
exit nest = 28.88;
remain with
in the
maternal
nest, contact
nest = 7.48; was seen
P < 0.05; in the
unless with
by the pups when
exit
scatter
P’s < 0.001).
removed
experimentally.
the pups, more calling
is in the nest. It can be seen in Fig. 3 that emitted
relative
exit the nest in the disturb
and
(F(1,20)
nest = 25.65;
than outside
To determine
There was a
disturb
or the pups were scattered,
condition
A further
is associated
vocalizations
between
and
P < 0.001).
Nest building increased when the nest was disturbed to the control condition (F(1,20) = 32.86; P < 0.001). condition
control
the mother
many
If
would more
was inside the nest
P < 0.001). calling
broadband
and other behaviors
calling
was associated
Pearson correlations were calculated between pattern, using scores from each test as a unit.
broadband
with other calling
behavioral
and each other
patterns, behavior
264
”
IN NEST
OUT OF NEST
LOCATION OF MOTHER
Fig. 3. Frequency of occurrence of broadband vocalizations emitted when the mother was either inside or outside of the nest.
Broadband calling was correlated significantly with locomotion (r(33) = 0.37; P < 0.05) and pup licking (433)
P < 0.001) P < 0.001)
= 0.66;
self-grooming (r(33) = - 0.55; Correlations
between
the frequency
behavior patterns were recalculated
but was negatively correlated with the mother’s and eating (r(33) = - 0.44; of broadband
P < 0.05).
calling and frequencies
those occurring outside. Pup calling was highly correlated with locomotion inside the nest (r(33) = 0.71;
P < 0.001);
to pup calling and locomotion
P < O.OOl), correlated 0.05).
of the mother
a smaller correlation was observed with respect
outside the nest (r(33) = 0.38;
calling correlated highly with immobility outside (r(33) = 0.05;
of other
to distinguish responses occurrjng in the nest from
P < 0.05).
Similarly, pup
inside the nest (r(33) = 0.58; P < O.OOl),
NS). Calling correlated
but not
with licking inside the nest, (r(33) = 0.72;
but not with licking outside (r(33) = 0.08; both inside and outside the nest (r(33)
NS). Nest building and calling were inside = 0.47;
outside = 0.42;
P’s <
The females used in this study appeared to display normal maternal behavior, retrieving pups, crouching on the pups and, apparently, nursing. Broadband calling occurred at about the same levels in all three observation conditions, and was not associated exclusively with one pattern of maternal activity, such as nursing or retrieval. Although
there
was no change
in the
number
of calls emitted
across the three
conditions, other evidence indicated that broadband vocalizations occurred when the mother interacted with her pups. Most broadband calls were recorded when the mother was in the nest. In addition, broadband calling correlated highly with locomotion, immobility, licking and nest-building by the mother. With the possible exception of nest-building,
265 these behaviors usually occurred when the mother was in close contact with the pups. It is likely that the mother steps on the pups, moves them and manipulates them during these activities.
Experiment 3 Broadband vocalizations seem to be associated with maternal contact with the pups or movement
on the pups. If broadband
vocalizations reduce the female’s incidental contact
with the pups, then they should be more likely to move or step on the pups when unable to hear the call. In this experiment, attenuated addition,
the ability of the female
by the use of earplugs. Some additjonal
to hear was temporarily
contact behaviors were analyzed.
ultrasonic vocalizations were monitored concurrently with broadband
In
calls, using
the bat detector. Subjects and apparatus The females used in the previous experiment way as the previous experiment,
were mated again and treated in the same
with one exception. On day 1, prior to testing, litters were
culled to 6 pups, to allow the experimenter
a better opportunity
to observe when the
mother was in contact with a pup. The test apparatus was identical to that used in the previous experiment. Ear p/u~ing Females received ear plugs that can attenuate sounds by about 45 dB in rats (Thomas et al., 1981).
Two to three hours before testing, the female
was lightly anesthetized
with
Metofane.
Each external acoustic meatus was filled with a medical ear mold compound
(Tru-Mold
Plastics, New York, NY). As the mold began to solidify, the pinnae were closed
with wound clips. Immediately under light Metofane
after the test was completed,
the ear plugs were removed
anesthesia. In control tests, females were anesthetized
prior to testing
but did not receive ear plugs. Prior to testing, females in both plug conditions were tested for their ability to hear broadband the aquarium
calls. A pup from another litter was held to the edge of
opposite the female and rotated (re: Experiment
calling for IO s. We observed whether the female approached
1) to induce broadband
the source of pup calls. This
procedure was repeated 5 times for each female. Design and pr~~dure All mothers and litters were tested twice, once on each of days 2 and 3 postpartum; the day of birth was day 0. Five of the 11 females received plugs on the first test; the remaining 6 received plugs on the second test. In both tests, each litter was tested in the control, disturb and scatter conditions. Behavior
recorded
In addition to the behavior patterns observed in Experiment
2, the following responses
were monitored: Wriggling:
wriggling movements of the pups.
Stepping:
The mother steps on one or more of the pups.
Adjust Crouch:
The mother changes her position while crouched over the pups. In the previous experiment, this response was included in the category ‘locomotion’.
266 TABLE 2 Mean frequency and control
of occurrence
conditions
of behavior
of Experiment
patterns
3, while
of the mother
the mother
and pup in the hearing attenuated
was inside
the nest (standard
errors
in
parentheses) Deafening
condition
Control Crouch
P<
F
Deafened (2.16) (0.14)
0.18 _ 2.38
*
(I ,291 (I .29)
4.10 0.43
0.05 *
70.18 0.42
8.88 (1.21) 7.73 (I .I 7)
12.09 8.81
Nest build
1.36 (0.33)
4.79
(0.95)
14.13
Push
0.61 (0.22)
1.63
(0.57)
2.66
Look at pups Step on pups Move Remain still
11.33 (2.06) 0.21 (0.08)
Lick pups
4.48 (0.90)
4.18
(0.60)
0.08
Self-groom
1.42 (0.28)
2.79
(0.66)
4.48
Eat
0.03 (0.03)
0.15
(0.10)
1.28
2.54 (0.62)
Retrieve
3.82
(I .I 8)
102.21
(15.74)
6.99
3.36 (0.94)
4.36
(7.70)
0.44
Enter nest Exit nest
4.61 (0.53) -
5.27
(0.65)
1.80 _
Wriggle
4.51 (5.94)
6.48 (1.33)
Ultrasonic
calls calls
59.15
0.05
1.65
(7.70)
Broadband
0.001
5.24
0.05 *
0.05 *
Push:
The mother pushes/manipulates
Orient:
While standing still outside the nest, the mother looks towards the
a pup with her snout.
Ultrasounds:
nest. Ultrasonic calls were monitored
in all tests, using the bat detector.
Results Pretests Plugging the female’s ears reduced her ability to hear broadband the pup emitted broadband
(median = 0) than if she was not (median = 2.5). a reliable difference
vocalizations.
When
calls, the female was less likely to approach if she was plugged
between
A Wilcoxon
test indicated that there was
the females in the plug and control tests (T = 0; n = 8;
P < 0.01).
Results of deafening There was little difference
in maternal
behavior observed in this experiment
and the
previous one. For this reason, only comparisons between the ear plug and control condition will be presented here. The difference between the ear plug and control condition for each behavioral measure are presented on Table 2 when the mother was inside the nest and on Table 3 when the mother was outside the nest. Also shown are the F and P values from the ANOVA comparing the plug and control conditions.
267 TABLE 3 Mean frequency
of occurrence of behavior patterns of the mother and pup in the hearing attenuated
and control conditions
of Experiment
3, while the mother was outside the nest (standard
errors in
parentheses) Deafening
condition
Control
Deafened
Crouch
0.03 (0.03)
Look at pups Step on pups
0.00
8.97 (1.23)
5.54 (I .05)
6.54
0.06 (0.06)
0.15 (0.11)
0.59
15.19 (1.87)
Move
7.12 (I .I 9)
Remain still
P<
F
0.03 (0.03)
0.05
10.76 (I .50)
7.15
0.01*
4.61 (1.06)
5.19
0.05
Nest build
6.88 (I .I 9)
6.88 (0.98)
0.00
Push
0.12 (0.12)
0.06 (0.04)
0.22
Lick pups
0.00 (0.00)
0.06 (0.04)
2.73
6.79 (1 .I 4)
0.011
Self-groom
17.27 (1.08)
Eat
0.81 (0.25)
1.06 (0.24)
0.57
Retrieve
1.33 (0.36)
0.91 (0.23)
2.56
Broadband calls Ultrasonic calls
5.76 (1 .lO) 6.21 (1.9-l)
6.76 (I ,311 4.39 (1.65)
0.50 0.73
Enter nest
_
_
Exit nest
4.45 (0.56)
4.64 (0.72)
0.07
Wriggle
7.88 (I .44)
7.30 (I .73)
0.14
* _
While inside the nest, the female showed increased locomotion deafened.
and nest-building
when
Outside the nest, the hearing impaired female was less likely to look at the nest
and she also had lower scores on both the immobility
and remain still measures, when
deafened. Statistical analyses revealed measures, deafened
presented
on Table
a significant deafening x test order interaction 4. In most cases, there
were
differences
for some
between
the
and control conditions on the first day of testing but not on the second. When
TABLE 4 Frequencies of occurrence
of behavior patterns in the control and deafened
groups on the first day of
testing Control
Deafened
P<
F
Female inside nest Look at pups
0.00 (0.13)
1.27
(0.63)
11.27
0.01
Step on pups
0.28 (0.13)
0.80
(0.28)
7.01
0.05
Nest build
1.44 (0.41)
4.86
(1.21)
6.40
0.05
Self-groom
1.72 (0.39)
4.67
(1.21)
10.37
0.01
74.22 (9.74)
155.53
(27.37)
45.34
0.001
Broadband calls female
outside nest
Look at pups
9.33 (I .85)
3.93
(I .74)
7.39
0.01
No move
7.00 (I .75)
2.87
(I .I41
6.39
0.05
268 there was a statistically reliable difference between the deaf and control conditions on the first day of testing, the means of the plug and control conditions are presented on Table 4, as is the result of a post hoc orthogonal contrast between the deafened and control groups. In the first test, it can be seen that pups emitted when the female was deafened.
many more broadband
In addition, the deafened
at the pups and step on the pups while she was in the nest. Nest-building ing also increased when the mother was deafened.
vocalizations
female was more likely to look and self-groom-
When the mother was outside the nest,
she was less likely to look at the pups when deafened. more likely to remain immobile than were the deafened
In addition,
control females were
animals.
Discussion Deafening
of the mother appears to affect behavior patterns associated with contact
with the pups. Locomotion
in the nest increased in the deafened condition on both test
days. Although mothers stepped on their pups somewhat infrequently, they were more likely to do so if they were deafened on the first day of testing. Outside the nest, the mothers were less attentive to the pups, looking at them less. In another study, White et al. (1992)
found that maternal females engaged in more incidental contact when pups were
rendered
unable
to vocalize.
However,
behavior patterns such as nest-building. cues originating associated with deafening,
deafened
from the nest rather than from broadband
mothers
performed
other
maternal
Perhaps these mothers were more responsive to the pups. Certain
calling, such as licking and retrieval,
behavior
were
patterns
not affected
by
perhaps because the females were responding to visual and olfactory cues.
The interaction of test order and deafening may reflect changes due to repeated testing. Possibly, mothers could
become
more sensitive to cues emitted
by the pups in other
modalities. On the other hand, pups emit fewer broadband vocalizations after the first few days of life (Okon, broadband
1972;
Experiment
2), and the mothers may become less responsive to
calls.
In the pretest, females were less likely to approach a source of broadband vocalizations when deafened,
attesting to the efficacy of the ear plugging procedure.
results indicate that the vocalizations
may evoke approach
possibility that should be investigated
in a larger cage.
In addition, these
behavior from the mother, a Broadband
calling
may have
contextually specific effects. Although it reduces incidental contact when the pup is in close proximity, it may attract the mother from a distance. During testing, the female was probably responding to broadband pure ultrasounds. Many more broadband more, broadband
pup calls rather than
calls were recorded than ultrasounds. Further-
calls tended to occur when the female was in the nest and therefore in
contact with the pups. It will be recalled from Experiment
1 that few ultrasonic vocaliza-
tions were emitted on day 2 in any of the conditions in which the pups were handled.
General
Discussion
Broadband pup vocalizations occurred when the female was in contact with the pups, especially when she moved on the pups or manipulated them. It was associated with locomotion of the female in the nest, stepping on the pups, licking the pups and nest entries. Deafening of the female increased these contact behaviors, at least on the first day
269
of testing. These findings
are consistent
(1986)
incidental
who
found
devocalized
with
with White
contact
et al. (I 992) and Ehret and Bernecker
by the
mother
increased
when
pups
were
in rats and mice respectively.
Okon
(I 972)
response
that
and
to rough
incidental
Elwood
handling
contact,
handling.
the
McCauley
care should
Pups may emit broadband Nonetheless,
and
by maternal
be taken
calls reflexively
pup
may
emit
terminate
in response
broadband
it) is loud
the aversive
to aversive
behavior.
that
pups
the broadband
may
such contact
vocalization
in response
position. to aversive
and has frequency
in both the sonic and ultrasonic
it could
startle the recipient
Should a pup be attacked
in
as rough handling.
and of long duration,
contact,
call
call is associated
they are not held in a horizontal
at the rat’s highest levels of sensitivity
If it is emitted
suggested
While
in defining
when
the
The call (as we observed
components
(1983)
females.
by a predator
ranges.
or otherwise
or an infanticidal
male in the mother’s absence, the mother could return to the nest to defend her litter. The results of the current vocalizations has suggested numerous call,
paper
and White
in rat pups affect incidental that
audible
with
few
there
are two
structurally
and ultrasonic
ultrasonic
bands,
components,
towards
the mother’s
nipples.
without
higher
frequency
situation
further,
Elwood
et al. (1992)
maternal
contact.
different
occurs
components
may
and McCauley
with
when
Haack et al. (1983) calls. One
maternal
handling;
pups struggle (1986),
affect
(1983)
show that broadband
broadband
is associated
Ehret and Bernecker
clearly However,
in the
however,
maternal
rat pup vocalizations ultrasonic
did not. In the current
broadband
bands. There are several possible explanations
the call examined potentially
in this study,
influences
nursing
between
littermates;
interactions
hear.) On the other may
study,
change
or other
maternal
however,
development.
behavior
distinct
patterns.
the
6-day-old
components,
vocalizations
pups emit broadband
but the
generally
had
In addition
broadband
to
call that
(It may also influence
calls long before they can
of the call may differ across species and strains, or
The apparent
of the pup relative
To confuse
for the discrepancy.
may be a structurally
hand, the structure
during
reflect the position
there
nest or push
by handling
rat and mouse pups. Calls from the mouse pups had high frequency
with
the other
show that the call
handling.
present calls evoked
call,
differences
to the microphone
in call structure
or the intensity
may
also
of the call; while
lying in the nest, or attempting to nurse, some components of the call may be muffled nest material or the bodies of the mother and/or littermates. Apart from the question in this study are generally al. (1983) base
broadband
in the
audible
calls are emitted
during
the age of weaning. are emitted occur during
harmonically
related
with the earlier
(Noirot,
to an audible
a structurally
1971; band
Okon,
related authors
in older reports:
Haack et
sweeps, with report
that
a
the
to handling,
pups approaching
only broadband
calls
calls and pure ultrasounds
were observed simpler
1972)
(Elmwood
calls, the calls
(1972),
days of life in response
calls reappear
on day 5, and only ultrasounds
may be a pure ultrasound
most
on day 2, both broadband
4 to 7 days, pups emit
by Okon
harmonically
In general,
the first few
Our results are consistent
handling
After about
range.
suggests that broadband
in response to handling
range of the broadband
to those reported
long, unmodulated
low
Okon (1972)
frequency
in structure
and others. All contain
frequency
although
of the upper similar
by
on day IO.
call when
handled.
This call
or it may consist of an ultrasound
and McCauley,
1983;
Haack
et al.,
1983). At any rate, this call has many fewer component than the broadband call. The broadband call does not have characteristics that facilitate localization (Marler, 1955,
1957;
and highly
Marler modulated.
and Hamilton,
1964).
The broadband
Calls that are easily localized
calls, however,
are generally
short
are of long duration and relatively
unmodulated;
they share some structural characteristics of alarm calls of some bird species
which emit alarm calls on encountering
predators (Marler,
1955,
1957).
These calls alert
conspecifics to the presence of a predator without providing information about the location of the caller. Some mammalian
calls that facilitate localization
by a conspecific differ in
structure from those that do not; female hamster calls are shorter and more modulated than some male calls. In hamsters, female calls attract a male from a distance whereas male calls are often emitted
in close proximity to the female and influence the female sexual
response (Floody and Pfaff, 1977). Taken together,
this study has shown that broadband
vocalizations
can be reliably
elicited from pups, especially during the first few days of life. In addition, it is clear that the calls are associated with maternal contact that regularly occurs during normal pup rearing: movement
on the pups, nest entries, stepping on pups, and after retrievals. There is some
evidence that the female is more likely to avoid contact with the pups if she is unable to hear the pup’s broadband
vocalization,
relationship of the pup’s broadband
especially in the first few days after birth. The
vocalization and pup age remains to be elaborated.
Acknowledgements This research was supported
by NIH and NSF grants to R.J.B. R.I., now a graduate of
Yale Medical School, received an award from the Henry Rutgers Thesis Committee senior research program. N.R.W.
Charles and Joanna Busch fund for Biological Research at Rutgers Universi~. with the Research Department
for his
received a portion of his post doctoral stipend from the
of the Metropolitan
He is now
Separate School Board (Toronto).
We
are grateful for the helpful suggestions of Alison Fleming concerning this project.
References Allin, J.T. and Banks, E.M., 1971.
Effects of temperature
on ultrasound production
by infant albino
rats. Dev. Psychobiol., 4: 149-156. Barfield,
RJ., Auerbach,
P., Ceyer,
sexual behavior. Am. Zool., Ehret, G. and Bernecker,
musccdis): Wri~ling Elwood,
R.W.
C., 1986.
Low frequency
calls release maternal
and McCauley,
Elwood (Editor),
L.A. and McIntosh,
T.K.,
1979.
Ultrasonic
vocalizations
in rat
19: 469-480.
P.]., 1983.
sound communication
behaviour.
Anim.
Communication
by
mouse pups (Mus
Behav., 34: 821-830.
in Rodents:
Parental Behavior of Rodents, Wiley, Chichester,
infants to adults.
In R.W.
England and New York, NY, pp.
127-149. Floody, O.R.
and Pfaff, D-W.,
1977.
Communication
among hamsters by high frequency
signals: 1. Physical characteristics of hamster calls. J. Comp. Haack,
B., Markl,
H. and Ehret, C. 1983.
J.F. Willott (Editor), The Auditory
Physiol. Psychol., 91
Sound communication
between
acoustic
: 794-806.
parents and offspring. In
Psychobiology of the Mouse. Charles C. Thomas, Springfield,
IL,
pp. 57-97. Marler,
P., 1955.
Marler,
P., 1957.
Characteristics of some animal calls. Nature, Specific distinctiveness
176: 6-8.
in the communication
signals of birds. Behaviour,
11:
13-39. Marler,
P. and Hamilton,
Noirot, E., 1968. 129-134.
W.J., 1964.
Mechanisms
of Animal
Behavior, Wiley,
NY.
Ultrasounds in young rodents. II. Changes with age in albino rats. Anim. Behav., 16:
271 Noirot,
E., 1972.
Ultrasounds
Nyby, J. and Whitney,
and maternal behavior in small rodents. Dev. Psychobiol,
G., 1977.
Ultrasonic
communication
of adult myomorph
5: 371-387.
rodents. Neurosci.
Biobehav. Rev., 2: l-14. Okon,
E.E.,
1970.
The ultrasonic
responses of albino mouse pups to tactile stimuli.
1971.
The temperature
J. Zool.,
162:
485-492. Okon,
E.E.,
rats. J. Zool, Okon,
164:
E.E., 1972.
Factors affecting ultrasound
Oswalt, G.L. and Meier, C.W., vocalizations Sales, C.D.,
1975.
Ultrasound
behavioural situations.
J. Zool.,
Dev. Psychobiol.,
N.R.,
149-l
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64.
Communication
by Animals,
Chapman and Hall, London.
Comparative studies of the ultrasonic calls of infant murid rodents.
V. and Barfield,
Bull.
Psychonom.
R.J., 1981. Sot.,
Behavioral and physiological habituation to
17: 297-282.
Adox, R., Reddy, A. and Bar-field, R.J., 1992.
H.-M.
senschaften,
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Ultrasonic
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8: 129-135.
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Haroutunian,
an ultrasonic stimulus. White,
139-148.
and aggressive behaviour in rats and other small animals. Anim.
Sales, C.D. and Pye, D., 1974.
D.A.,
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Sales, G.D. and Smith, J.L., 1978. Thomas,
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197213. Ultrasound
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Olfactory, thermal and tactual influences on infantile ultrasonic
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Naturwk
BEPROC
257
00563
Pup’s broadband vocalizations and maternal behavior in the rat Richard Ihnat, Nicholas Department
of Biological
R. White and Ronald J. Barfield *
Sciences, Busch Campus,
Rutgers University,
Box 1059,
Piscata way NJ, 08855- 1059, USA
(Accepted
25 March
1994)
Abstract
Rat pups emit broadband the ultrasonic under
which
the calls are emitted,
female’s
behavior.
different
ways.
the horizontal Vocalizations into contact
vocalizations
range. Three experiments
undertaken
extending
Broadband plane.
calling
and the effects that they
when
occurred
In a second study, the mother
occurred
most often when
might
was observed engaged
moving
while
have on the maternal in several
up and moved
interacting
in behaviors
that brought
Key words:
to reduce
Contact;
rough handling
Maternal
behavior;
or inadvertent
contact
Pup; Broadband
her In
to controls, deafened only if the female was
during the first of two tests, when the pups were two days old. Broadband
may function
off
with her litter.
in the nest, and pup licking.
temporarily deafened. Relative contact with the pups, although
to
the circumstances
by the experimenter
the pup was picked
the mother
with the pups, such as nest entry,
from the audible
to determine
In the first study, pups were manipulated
another experiment, females were females engaged in more incidental deafened
with components were
calling
by the mother.
vocalization
Introduction Ultrasonic
vocalizations
are employed
ubiquitously
by rodents
during
social
behavior
such as sex and aggression (Barfield et al., 1979; Nyby and Whitney, 1977, Sales, 1972a,b; Sales and Pye, 1974). Rodent pups of a variety of species produce calls, often in the
* Corresponding author. SSDI 0376-6357(94)00028-F
258
ultrasonic
range,
but sometimes
Sales and Smith, associated
with
1978).
in the range audible
Two patterns
isolation
of calling
and the other with
One pup call, a pure tone of 40-50 rats and mice when Sales and when
Zippelius
the pups are developing
and Banks, 1971; Okon,
maternal
Schleidt,
homeothermy
1971;
and 4-65
and cold (Noirot,
and Oswalt
(Sales and Pye, 1974; extensively
1968;
1956).
ms duration
Oswalt
Maximal
occur in 1975;
and Meier,
ultrasonic
and are most susceptible
and Meier,
in rats, one
handling.
kHz in frequency
pups are isolated
Pye, 1974;
to humans
have been studied
calling
occurs
to cold stress (Allin
1975).
When rat pups are handled, they emit both audible and ultrasonic calls (Noirot, 1971; Okon, 1972). The audible calls were similar in structure to the broadband calls described below.
Okon
between both
(1972) and after
audibly
when
picked
up
characterized
levels
a broadband
Okon
mother
of the
‘wriggling’
bands
had frequencies
IO kHz with
behavior
Haack et al. (1983)
reported
few ultrasonic
when
components,
in response
to handling pups called
mouse
and
came
(rolled
Bernecker
unmodulated
into contact
and changing
harmoni-
with
the pup.
Another
pups pushed for mothers’
was at
associated
position
calls. One call, with handling.
over, (1986)
Most of the energy
These calls were
nest-building
when
Ehret
aged
that
numerous
components. broadband
in pups
by the experimenter
0.5 and 4 kHz.
rough maternal
occurred
emitted
recently,
the mother
between licking,
with
handled
More
in evidence
also observed
call in mice with
two similar
up to 80 kHz was associated
most
calls were
and
no ultrasonic
that included
were
(1970)
neck).
sweeps that was emitted
below
maternal
by the
scruff
ultrasounds
days; audible
this period.
retrieved
by the
cally related
that
days and 14-16
4-5
before
The lowest
observed
with
on the nest.
bands extending
broadband nipples
call, with or struggled
in the nest. Elwood and McCauley (1983) reported a broadband pups containing a low band of about 1 kHz in frequency reached
the ultrasonic
these broadband similar
range.
Elwood
vocalizations
during
aversive
maternal
contact.
by pups of other
species,
including
mice. The mouse
calls emitted
had components The current reliably elicited
in the ultrasonic
behavior.
A further
of the mother
Broadband
suggest that rat pups generally These authors
experiment
emit
describe
call, however,
range.
study was undertaken to determine whether broadband from rat pups and whether they occurred in conjunction
deafening
Experiment
and McCauley
‘audible call’ from 6-day-old rat with several harmonics that rarely
was performed
on maternal
to determine
calls could be with maternal
the effects
of temporary
behavior.
1 vocalizations
were tape recorded
tally. In addition, pups were handled calls could be elicited reliably.
from rat pups and analyzed
in specific
ways to determine
spectrographi-
whether
broadband
Subjects Eighteen pups were drawn from the litters of three Long-Evans female rats. About two weeks after their arrival in the laboratory, each female was inseminated by a vigorous stud male. Until the final week of pregnancy, females were individually housed in the rat colony. They were then transferred to 48 x 25 X 30 cm glass aquaria in a separate room. Each mother remained in her aquarium with her litter until the end of the experiment.
259 Food, water and nesting materials on a reverse
were continually
12 : 12 light cycle with
available.
lights out at IO:00
The animals were maintained
h.
Apparatus Pups were tested in a 68 X 32 X 32 cm polyethylene monitored
through
converts
ultrasounds
Vocalizations located
35
recorded
over
the
pass filter,
center
equipment
spectrographically
receiver
tub.
The
Kjaer 4135
Hz and 100 ktiz.
cm)
per second
had a flat response analyzed
with
detector’),
condenser
mic:rophone,
to a Bruel and Kjaer 2160 measuring
(76.2
vocalizations
(‘bat
were which
range.
a Bruel and
of the
tub. Ultrasonic
heterodyne
audible
through
set to 2000
at 30 inches
recording
a QMC
into the humanly
was coupled
band
running
with
were
cm
preamplifier, 3550
earphones
which
amplifier
A Lockheed
and
tape
recorder
the vocalizations.
to at least 100 kHz. Taped Sonagraph
in
and a Krone-Hite
Store-4
was used to record
a Kay Digital
microphone
has a built
All
vocalizations
a Uniscan
were
II continuous
sound spectrograph. Design Each pup was tested once only, There were
either
9 pups in each age group:
litters. Each pup was given 4 handling pick up, back and forth preliminary
on day 2, 5 or 10 (the day of birth was day 0).
3 pups were treatments
and rotation,
drawn
in a random
randomly
from each of the 3
order:
based on the procedures
no handling
of Okon
(control),
(1972)
and our
observations.
Procedure Pups were undisturbed interval ink,
removed
of about
so that
recorded
from
for 5 min
the
litter
would
not
taken
to a testing
Each test lasted
3 min. After testing,
they
and
acclimatization.
pups returned
be tested
again.
room.
pup was gently
to the litter,
Vocalizations
left
by an
after being marked
from
the
with
pups were
tape
test, pups were simply
left on the floor of the tub. In the ‘pick up’ test, the
lifted 3 cm from the floor of the tub by the nape of the neck and put down
at the end of the 15-s interval.
In the ‘back and forth’
condition,
the pups were
3 cm from the floor of the tub by the nape of the neck and moved on
a horizontal
movement
plane
for
a distance
of 10 cm.
were made over the 15-s test period.
lifted between was rotated
two fingers by the nape of the neck and rotated
A spectrograph
of a typical
pup audible
5 to
7 back
condition,
picked
up
back and and
forth
the pups were
to an angle of 45”. The pup
call is shown
in Fig. 2. For statistical to an analysis
purposes,
of variance.
on Fig. 1. It contains
from 2 to 64 kHz, thus with components
The mean number of ultrasonic and broadband subjected
About
In the ‘rotation’
rhythmically
5 to 7 times in each test.
slightly modulated sweeps extending sonic and ultrasonic ranges. shown
were
in all tests.
In the control
forth
They
15 s, and was separated
all data
a series of in both the
calls in each age and test condition were
Post hoc orthoganal
transformed contrasts
logarithmically were
performed
is and as
TIME IN MSEC
Fig. 1. Sound spectrograph
of a typical
BROADBAND
pup broadband
call.
PUP VOCALIZATIONS
DAY 2
IJ
CONTROL
E
PICK UP
q
BACK AND FORTH
DAY 10
DAY 5 DAY OF TESTING
ULTRASONIC
PUP VOCALIZATIONS
DAY 2
DAY 5
DAY 10
DAY OF TESTING
Fig. 2. Frequency
of occurrence
of audible
handling
broadband
condition
r
calls and
ultrasonic
and at each age level.
vocalizations
in each
261 necessary.
There
was
a reliable
x test
handling
interaction
for
both
ultrasonic
calling
(F(6,70) = 7.27; P < 0.001) and broadband calling (F(6,70) = 23.48; P < 0.001). On day 2, ultrasonic calls occurred much more often in the control condition any other condition
(F(1,70)
= 49.34;
P < 0.001).
At age 5 days, there were
than
in
no significant
differences across handling conditions (F(1,70)= 2.59; NS). On day 10, pups emitted more ultrasonic calls in the rotation condition than in any other condition (F(1,70)= 5.11; P<
0.05). Broadband
(F(1,69)
calling
day
calling
was higher
broadband
generally
2 = 229.74;
when the pup was rotated
occurred
day
5 = 148.60;
P’s < 0.001).
on day 2 than day 5 (F(1,69)
calls were
negatively
correlated
= 17.00;
with
on test days 2 and 5
During
rotation,
P < 0.001).
ultrasonic
broadband
The occurrence
calls (r(l05)
= -0.32;
of P <
0.001).
In general, reported Bernecker range
the vocalizations
by Elwood (1986) ultrasonic
!&day-old
bands.
components
pups. Broadband
day 5 or the characteristics Broadband
whether Noirot
up
and
the broadband (1972)
Okon
occurred
(1972)
5 and ultrasonic consistent
structurally
and McCauley
from 6 day old pups, whereas
similar
calls may contain
fewer
ultrasonic
to those
and Ehret and
reports on the upper
reported
broadband
calls
we taped
calls from 2- and
frequency
components
after
of the call may differ across strains.
calls can be reliably
picked
were
in rats and Haack et al. (1983)
In rats, Elwood
elicited
up by the nape of the neck and rotated; merely
in this study
(1983)
in mice. In both rats and mice, there are conflicting
of the harmonic
without
recorded
and McCauley
moved
from pups aged 2 and 5 days old when
horizontally.
These
calls reported
by Elwood
when
mothers
rodent
noted that audible calls occurred
with those of Okon,
picked
it does not occur if the pup is left undisturbed observations
and McCauley
moved
calls occurred
their
raise the
question
(19831, Okon
of
(1972) and
pups off the horizontal
in response to handling
or
plane.
prior to day 4 or
at a later age. The results of the present study are relatively in that broadband
calls occur at higher levels on day 2 than
on day 5, and not at all on day 10. Our that
results are not entirely
only
broadband
broadband
calls occur
ultrasounds handling.
are emitted,
Experiment A detailed tions occur
consistent
calls are elicited in response whereas
with
Elwood
by handling,
to handling.
on day 10, only
On
and McCauley’s
(1983)
not
ultrasounds.
day
5, both
ultrasounds
On
suggestion day
broadband
are emitted
2, only calls and
in response
to
2 ethological in relation
analysis was undertaken to maternal
behavior
to determine
when
broadband
vocaliza-
patterns.
Subjects Thirteen experiment.
females
were
mated
and
On the first day, postpartum
maintained
in the
litters were culled
manner
described
to 10 pups.
in the
first
262
Apparatus Mothers
and litters were
the tape recording a 20 channel
observed
equipment
in their
home
aquaria.
was not used; instead,
Esterline Angus event
Unlike
behavioral
the first experiment,
events were recorded
with
recorder.
Design and procedure At least 2 h prior to testing, the aquarium an adjoining
testing room.
and litter was observed ‘control’
condition,
for three
5-min
third control
the mother
was maintained
for 15 min under three conditions.
the nest was left undisturbed
periods,
separated
during
by an interval
and litter was moved
the nest material
During
the first observation,
observation.
for 15 min without
interruption.
from
and the pups were
the aquarium
(‘scatter’
condition).
returned
to the aquarium,
interruption.
After
another
condition). 15 min
scattered
evenly
The nest was also moderately and the mother
Testing occurred
Fifteen
min after the
the pups within
the
The litter was then observed
break,
the mother
over the floor
disturbed.
and litter
the
Litters were observed
of IO to 15 min.
(the ‘disturb’
to
at 22°C _t 2°C. Each female
test, the nest was stirred up with a long metal rod, moving
nest and disturbing
Behavior
containing
Room temperature
The female
were
observed
was removed
of the aquarium was immediately
for 15 min without
when the pups were 2 days old (day of birth is day 0).
recorded
Retrieval:
The female
picks up a pup in her mouth
Licking:
The mother
licks the pup. Licking was often accompanied
Nest Building:
lation of the pup. The female transports nesting material
material
around
The female
licks or cleans herself.
Eating:
The female
chews food,
Locomotion:
The female engaging
by manipuor pushes
her nose or paws.
feces or nesting material.
or adjusts
in any other
it to the nest.
into the nest in her mouth,
the nest with
Grooming:
moves
and returns
her body
behavior
pattern
position. described
If the female
was
in this list, locomo-
tion was not scored. The
Immobility:
female
movements.
was
motionless,
While
the pups and appeared immobility behavior
observed
Emission of broadband
Vocalization:
purely
ultrasonic
for
breathing
or
frequently
minor
head
crouched
over
to be nursing. As in the case with ‘locomotion’,
was not scored pattern
except
in the nest, the female if the female
was engaging
in any other
in this study.
vocalizations
vocalizations
by the pups. The occurrence
of
was not recorded.
Results Statistical
analysis revealed
of the control observation
condition;
no significant
difference
thus the results were
totalled
between
the 3 observation
and treated
as a single
periods 15min
period.
Frequencies of each behavior pattern are shown on Table 1. An analysis of variance (ANOVA) was performed for each behavioral measure; the F and P values are reported in Table 1. When appropriate, individual post hoc tests (orthogonal comparisons) were
263 TABLE 1 Mean
frequency
Experiment
of occurrence
of behavior
patterns
by the mother
and pups in each condition
Disturbance
condition
Control
P<
F
Scatter
Disturb
Move
39.72
(3.08)
31.36
(I ,431
33.54
(1.41)
Remain still
34.91
(4.13)
18.64
(2.74)
10.91
(I .85)
26.01
0.001
Retrieve
0.09
(0.18)
1.82
(0.57)
10.45
(0.72)
71.63
0.001
Lick pups
6.91
(1.98)
4.73
(1.58)
3.09
(0.90)
0.27
Nest-building
2.91
(I .28)
10.82
(2.35)
13.00
Eat
0.45
(0.24)
0.73
(0.38)
0.64
(0.31)
Enter nest
2.82
(0.04)
5.27
(0.96)
10.64
(0.70)
28.45
0.001
Exit nest
1.82
(0.51)
5.36
(0.97)
10.64
(0.68)
40.79
0.001
8.18
(1.27)
5.91
79.55 (15.75)
80.91
Self-groom Broadband
calls
4.27
(1.51)
87.00
(16.33)
are
in the text.
performed
and
performed
on the data prior to analysis.
reported
There were fewer to the control
the scatter O.OOl>,
incidences
condition
and disturb
and
= 10.62;
conditions
less likely
to be immobile
0.001
0.16
(I .I 2)
1.81 0.07
a logarithmic
transformation
and scatter conditions
NS). Mothers
than in the control
0.05
11.58
(11.20)
No difference
= 0.59;
3.75
(I .54)
in the disturb
P < 0.01).
(F(1,20)
condition again
If necessary,
of locomotion
(F(1,20)
in the disturb
immobile
of
error in parentheses)
3 (standard
condition
in the scatter
was detected were
relative between
less likely
(F(1,20)
condition
was
to be P <
= 16.41;
(F(1,20)
= 10.33;
P < 0.01). Retrieval, small
but
(F(1,20)
as might
be expected,
significant
= 4.35;
conditions
increase
P < 0.05).
(F(1,20)
increased
in retrieval
when
the pups were scattered.
between
the
There was a large difference
= 83.99;
Finally,
the
female
was more
likely
relative to the control
nest = 12.98;
P < 0.01).
condition
(F(1,20)
Location
of mother
Two-day-old broadband be expected broadband
enter
pups
calling when
generally
the mother were
(F(1,20)
= 26.53;
Correlations
between
broadband
whether
both
to enter
conditions
the disturb
and scatter
enter
increase
in both
measures
exit nest = 28.88;
remain with
in the
maternal
nest, contact
nest = 7.48; was seen
P < 0.05; in the
unless with
by the pups when
exit
scatter
P’s < 0.001).
removed
experimentally.
the pups, more calling
is in the nest. It can be seen in Fig. 3 that emitted
relative
exit the nest in the disturb
and
(F(1,20)
nest = 25.65;
than outside
To determine
There was a
disturb
or the pups were scattered,
condition
A further
is associated
vocalizations
between
and
P < 0.001).
Nest building increased when the nest was disturbed to the control condition (F(1,20) = 32.86; P < 0.001). condition
control
the mother
many
If
would more
was inside the nest
P < 0.001). calling
broadband
and other behaviors
calling
was associated
Pearson correlations were calculated between pattern, using scores from each test as a unit.
broadband
with other calling
behavioral
and each other
patterns, behavior
264
”
IN NEST
OUT OF NEST
LOCATION OF MOTHER
Fig. 3. Frequency of occurrence of broadband vocalizations emitted when the mother was either inside or outside of the nest.
Broadband calling was correlated significantly with locomotion (r(33) = 0.37; P < 0.05) and pup licking (433)
P < 0.001) P < 0.001)
= 0.66;
self-grooming (r(33) = - 0.55; Correlations
between
the frequency
behavior patterns were recalculated
but was negatively correlated with the mother’s and eating (r(33) = - 0.44; of broadband
P < 0.05).
calling and frequencies
those occurring outside. Pup calling was highly correlated with locomotion inside the nest (r(33) = 0.71;
P < 0.001);
to pup calling and locomotion
P < O.OOl), correlated 0.05).
of the mother
a smaller correlation was observed with respect
outside the nest (r(33) = 0.38;
calling correlated highly with immobility outside (r(33) = 0.05;
of other
to distinguish responses occurrjng in the nest from
P < 0.05).
Similarly, pup
inside the nest (r(33) = 0.58; P < O.OOl),
NS). Calling correlated
but not
with licking inside the nest, (r(33) = 0.72;
but not with licking outside (r(33) = 0.08; both inside and outside the nest (r(33)
NS). Nest building and calling were inside = 0.47;
outside = 0.42;
P’s <
The females used in this study appeared to display normal maternal behavior, retrieving pups, crouching on the pups and, apparently, nursing. Broadband calling occurred at about the same levels in all three observation conditions, and was not associated exclusively with one pattern of maternal activity, such as nursing or retrieval. Although
there
was no change
in the
number
of calls emitted
across the three
conditions, other evidence indicated that broadband vocalizations occurred when the mother interacted with her pups. Most broadband calls were recorded when the mother was in the nest. In addition, broadband calling correlated highly with locomotion, immobility, licking and nest-building by the mother. With the possible exception of nest-building,
265 these behaviors usually occurred when the mother was in close contact with the pups. It is likely that the mother steps on the pups, moves them and manipulates them during these activities.
Experiment 3 Broadband vocalizations seem to be associated with maternal contact with the pups or movement
on the pups. If broadband
vocalizations reduce the female’s incidental contact
with the pups, then they should be more likely to move or step on the pups when unable to hear the call. In this experiment, attenuated addition,
the ability of the female
by the use of earplugs. Some additjonal
to hear was temporarily
contact behaviors were analyzed.
ultrasonic vocalizations were monitored concurrently with broadband
In
calls, using
the bat detector. Subjects and apparatus The females used in the previous experiment way as the previous experiment,
were mated again and treated in the same
with one exception. On day 1, prior to testing, litters were
culled to 6 pups, to allow the experimenter
a better opportunity
to observe when the
mother was in contact with a pup. The test apparatus was identical to that used in the previous experiment. Ear p/u~ing Females received ear plugs that can attenuate sounds by about 45 dB in rats (Thomas et al., 1981).
Two to three hours before testing, the female
was lightly anesthetized
with
Metofane.
Each external acoustic meatus was filled with a medical ear mold compound
(Tru-Mold
Plastics, New York, NY). As the mold began to solidify, the pinnae were closed
with wound clips. Immediately under light Metofane
after the test was completed,
the ear plugs were removed
anesthesia. In control tests, females were anesthetized
prior to testing
but did not receive ear plugs. Prior to testing, females in both plug conditions were tested for their ability to hear broadband the aquarium
calls. A pup from another litter was held to the edge of
opposite the female and rotated (re: Experiment
calling for IO s. We observed whether the female approached
1) to induce broadband
the source of pup calls. This
procedure was repeated 5 times for each female. Design and pr~~dure All mothers and litters were tested twice, once on each of days 2 and 3 postpartum; the day of birth was day 0. Five of the 11 females received plugs on the first test; the remaining 6 received plugs on the second test. In both tests, each litter was tested in the control, disturb and scatter conditions. Behavior
recorded
In addition to the behavior patterns observed in Experiment
2, the following responses
were monitored: Wriggling:
wriggling movements of the pups.
Stepping:
The mother steps on one or more of the pups.
Adjust Crouch:
The mother changes her position while crouched over the pups. In the previous experiment, this response was included in the category ‘locomotion’.
266 TABLE 2 Mean frequency and control
of occurrence
conditions
of behavior
of Experiment
patterns
3, while
of the mother
the mother
and pup in the hearing attenuated
was inside
the nest (standard
errors
in
parentheses) Deafening
condition
Control Crouch
P<
F
Deafened (2.16) (0.14)
0.18 _ 2.38
*
(I ,291 (I .29)
4.10 0.43
0.05 *
70.18 0.42
8.88 (1.21) 7.73 (I .I 7)
12.09 8.81
Nest build
1.36 (0.33)
4.79
(0.95)
14.13
Push
0.61 (0.22)
1.63
(0.57)
2.66
Look at pups Step on pups Move Remain still
11.33 (2.06) 0.21 (0.08)
Lick pups
4.48 (0.90)
4.18
(0.60)
0.08
Self-groom
1.42 (0.28)
2.79
(0.66)
4.48
Eat
0.03 (0.03)
0.15
(0.10)
1.28
2.54 (0.62)
Retrieve
3.82
(I .I 8)
102.21
(15.74)
6.99
3.36 (0.94)
4.36
(7.70)
0.44
Enter nest Exit nest
4.61 (0.53) -
5.27
(0.65)
1.80 _
Wriggle
4.51 (5.94)
6.48 (1.33)
Ultrasonic
calls calls
59.15
0.05
1.65
(7.70)
Broadband
0.001
5.24
0.05 *
0.05 *
Push:
The mother pushes/manipulates
Orient:
While standing still outside the nest, the mother looks towards the
a pup with her snout.
Ultrasounds:
nest. Ultrasonic calls were monitored
in all tests, using the bat detector.
Results Pretests Plugging the female’s ears reduced her ability to hear broadband the pup emitted broadband
(median = 0) than if she was not (median = 2.5). a reliable difference
vocalizations.
When
calls, the female was less likely to approach if she was plugged
between
A Wilcoxon
test indicated that there was
the females in the plug and control tests (T = 0; n = 8;
P < 0.01).
Results of deafening There was little difference
in maternal
behavior observed in this experiment
and the
previous one. For this reason, only comparisons between the ear plug and control condition will be presented here. The difference between the ear plug and control condition for each behavioral measure are presented on Table 2 when the mother was inside the nest and on Table 3 when the mother was outside the nest. Also shown are the F and P values from the ANOVA comparing the plug and control conditions.
267 TABLE 3 Mean frequency
of occurrence of behavior patterns of the mother and pup in the hearing attenuated
and control conditions
of Experiment
3, while the mother was outside the nest (standard
errors in
parentheses) Deafening
condition
Control
Deafened
Crouch
0.03 (0.03)
Look at pups Step on pups
0.00
8.97 (1.23)
5.54 (I .05)
6.54
0.06 (0.06)
0.15 (0.11)
0.59
15.19 (1.87)
Move
7.12 (I .I 9)
Remain still
P<
F
0.03 (0.03)
0.05
10.76 (I .50)
7.15
0.01*
4.61 (1.06)
5.19
0.05
Nest build
6.88 (I .I 9)
6.88 (0.98)
0.00
Push
0.12 (0.12)
0.06 (0.04)
0.22
Lick pups
0.00 (0.00)
0.06 (0.04)
2.73
6.79 (1 .I 4)
0.011
Self-groom
17.27 (1.08)
Eat
0.81 (0.25)
1.06 (0.24)
0.57
Retrieve
1.33 (0.36)
0.91 (0.23)
2.56
Broadband calls Ultrasonic calls
5.76 (1 .lO) 6.21 (1.9-l)
6.76 (I ,311 4.39 (1.65)
0.50 0.73
Enter nest
_
_
Exit nest
4.45 (0.56)
4.64 (0.72)
0.07
Wriggle
7.88 (I .44)
7.30 (I .73)
0.14
* _
While inside the nest, the female showed increased locomotion deafened.
and nest-building
when
Outside the nest, the hearing impaired female was less likely to look at the nest
and she also had lower scores on both the immobility
and remain still measures, when
deafened. Statistical analyses revealed measures, deafened
presented
on Table
a significant deafening x test order interaction 4. In most cases, there
were
differences
for some
between
the
and control conditions on the first day of testing but not on the second. When
TABLE 4 Frequencies of occurrence
of behavior patterns in the control and deafened
groups on the first day of
testing Control
Deafened
P<
F
Female inside nest Look at pups
0.00 (0.13)
1.27
(0.63)
11.27
0.01
Step on pups
0.28 (0.13)
0.80
(0.28)
7.01
0.05
Nest build
1.44 (0.41)
4.86
(1.21)
6.40
0.05
Self-groom
1.72 (0.39)
4.67
(1.21)
10.37
0.01
74.22 (9.74)
155.53
(27.37)
45.34
0.001
Broadband calls female
outside nest
Look at pups
9.33 (I .85)
3.93
(I .74)
7.39
0.01
No move
7.00 (I .75)
2.87
(I .I41
6.39
0.05
268 there was a statistically reliable difference between the deaf and control conditions on the first day of testing, the means of the plug and control conditions are presented on Table 4, as is the result of a post hoc orthogonal contrast between the deafened and control groups. In the first test, it can be seen that pups emitted when the female was deafened.
many more broadband
In addition, the deafened
at the pups and step on the pups while she was in the nest. Nest-building ing also increased when the mother was deafened.
vocalizations
female was more likely to look and self-groom-
When the mother was outside the nest,
she was less likely to look at the pups when deafened. more likely to remain immobile than were the deafened
In addition,
control females were
animals.
Discussion Deafening
of the mother appears to affect behavior patterns associated with contact
with the pups. Locomotion
in the nest increased in the deafened condition on both test
days. Although mothers stepped on their pups somewhat infrequently, they were more likely to do so if they were deafened on the first day of testing. Outside the nest, the mothers were less attentive to the pups, looking at them less. In another study, White et al. (1992)
found that maternal females engaged in more incidental contact when pups were
rendered
unable
to vocalize.
However,
behavior patterns such as nest-building. cues originating associated with deafening,
deafened
from the nest rather than from broadband
mothers
performed
other
maternal
Perhaps these mothers were more responsive to the pups. Certain
calling, such as licking and retrieval,
behavior
were
patterns
not affected
by
perhaps because the females were responding to visual and olfactory cues.
The interaction of test order and deafening may reflect changes due to repeated testing. Possibly, mothers could
become
more sensitive to cues emitted
by the pups in other
modalities. On the other hand, pups emit fewer broadband vocalizations after the first few days of life (Okon, broadband
1972;
Experiment
2), and the mothers may become less responsive to
calls.
In the pretest, females were less likely to approach a source of broadband vocalizations when deafened,
attesting to the efficacy of the ear plugging procedure.
results indicate that the vocalizations
may evoke approach
possibility that should be investigated
in a larger cage.
In addition, these
behavior from the mother, a Broadband
calling
may have
contextually specific effects. Although it reduces incidental contact when the pup is in close proximity, it may attract the mother from a distance. During testing, the female was probably responding to broadband pure ultrasounds. Many more broadband more, broadband
pup calls rather than
calls were recorded than ultrasounds. Further-
calls tended to occur when the female was in the nest and therefore in
contact with the pups. It will be recalled from Experiment
1 that few ultrasonic vocaliza-
tions were emitted on day 2 in any of the conditions in which the pups were handled.
General
Discussion
Broadband pup vocalizations occurred when the female was in contact with the pups, especially when she moved on the pups or manipulated them. It was associated with locomotion of the female in the nest, stepping on the pups, licking the pups and nest entries. Deafening of the female increased these contact behaviors, at least on the first day
269
of testing. These findings
are consistent
(1986)
incidental
who
found
devocalized
with
with White
contact
et al. (I 992) and Ehret and Bernecker
by the
mother
increased
when
pups
were
in rats and mice respectively.
Okon
(I 972)
response
that
and
to rough
incidental
Elwood
handling
contact,
handling.
the
McCauley
care should
Pups may emit broadband Nonetheless,
and
by maternal
be taken
calls reflexively
pup
may
emit
terminate
in response
broadband
it) is loud
the aversive
to aversive
behavior.
that
pups
the broadband
may
such contact
vocalization
in response
position. to aversive
and has frequency
in both the sonic and ultrasonic
it could
startle the recipient
Should a pup be attacked
in
as rough handling.
and of long duration,
contact,
call
call is associated
they are not held in a horizontal
at the rat’s highest levels of sensitivity
If it is emitted
suggested
While
in defining
when
the
The call (as we observed
components
(1983)
females.
by a predator
ranges.
or otherwise
or an infanticidal
male in the mother’s absence, the mother could return to the nest to defend her litter. The results of the current vocalizations has suggested numerous call,
paper
and White
in rat pups affect incidental that
audible
with
few
there
are two
structurally
and ultrasonic
ultrasonic
bands,
components,
towards
the mother’s
nipples.
without
higher
frequency
situation
further,
Elwood
et al. (1992)
maternal
contact.
different
occurs
components
may
and McCauley
with
when
Haack et al. (1983) calls. One
maternal
handling;
pups struggle (1986),
affect
(1983)
show that broadband
broadband
is associated
Ehret and Bernecker
clearly However,
in the
however,
maternal
rat pup vocalizations ultrasonic
did not. In the current
broadband
bands. There are several possible explanations
the call examined potentially
in this study,
influences
nursing
between
littermates;
interactions
hear.) On the other may
study,
change
or other
maternal
however,
development.
behavior
distinct
patterns.
the
6-day-old
components,
vocalizations
pups emit broadband
but the
generally
had
In addition
broadband
to
call that
(It may also influence
calls long before they can
of the call may differ across species and strains, or
The apparent
of the pup relative
To confuse
for the discrepancy.
may be a structurally
hand, the structure
during
reflect the position
there
nest or push
by handling
rat and mouse pups. Calls from the mouse pups had high frequency
with
the other
show that the call
handling.
present calls evoked
call,
differences
to the microphone
in call structure
or the intensity
may
also
of the call; while
lying in the nest, or attempting to nurse, some components of the call may be muffled nest material or the bodies of the mother and/or littermates. Apart from the question in this study are generally al. (1983) base
broadband
in the
audible
calls are emitted
during
the age of weaning. are emitted occur during
harmonically
related
with the earlier
(Noirot,
to an audible
a structurally
1971; band
Okon,
related authors
in older reports:
Haack et
sweeps, with report
that
a
the
to handling,
pups approaching
only broadband
calls
calls and pure ultrasounds
were observed simpler
1972)
(Elmwood
calls, the calls
(1972),
days of life in response
calls reappear
on day 5, and only ultrasounds
may be a pure ultrasound
most
on day 2, both broadband
4 to 7 days, pups emit
by Okon
harmonically
In general,
the first few
Our results are consistent
handling
After about
range.
suggests that broadband
in response to handling
range of the broadband
to those reported
long, unmodulated
low
Okon (1972)
frequency
in structure
and others. All contain
frequency
although
of the upper similar
by
on day IO.
call when
handled.
This call
or it may consist of an ultrasound
and McCauley,
1983;
Haack
et al.,
1983). At any rate, this call has many fewer component than the broadband call. The broadband call does not have characteristics that facilitate localization (Marler, 1955,
1957;
and highly
Marler modulated.
and Hamilton,
1964).
The broadband
Calls that are easily localized
calls, however,
are generally
short
are of long duration and relatively
unmodulated;
they share some structural characteristics of alarm calls of some bird species
which emit alarm calls on encountering
predators (Marler,
1955,
1957).
These calls alert
conspecifics to the presence of a predator without providing information about the location of the caller. Some mammalian
calls that facilitate localization
by a conspecific differ in
structure from those that do not; female hamster calls are shorter and more modulated than some male calls. In hamsters, female calls attract a male from a distance whereas male calls are often emitted
in close proximity to the female and influence the female sexual
response (Floody and Pfaff, 1977). Taken together,
this study has shown that broadband
vocalizations
can be reliably
elicited from pups, especially during the first few days of life. In addition, it is clear that the calls are associated with maternal contact that regularly occurs during normal pup rearing: movement
on the pups, nest entries, stepping on pups, and after retrievals. There is some
evidence that the female is more likely to avoid contact with the pups if she is unable to hear the pup’s broadband
vocalization,
relationship of the pup’s broadband
especially in the first few days after birth. The
vocalization and pup age remains to be elaborated.
Acknowledgements This research was supported
by NIH and NSF grants to R.J.B. R.I., now a graduate of
Yale Medical School, received an award from the Henry Rutgers Thesis Committee senior research program. N.R.W.
Charles and Joanna Busch fund for Biological Research at Rutgers Universi~. with the Research Department
for his
received a portion of his post doctoral stipend from the
of the Metropolitan
He is now
Separate School Board (Toronto).
We
are grateful for the helpful suggestions of Alison Fleming concerning this project.
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