The recognition process and the basis for that recognition, in brown bats, between mother and infant are analyzed. Two parameters, ultrasonic communication and olfactory stimuli, are investigated. The test animals were not allowed any visual contact. It was concluded that individual recognition between mother and infant occurred. However, it could not be determined if the recognition was based on ultrasonic signals or olfactory stimuli

Gould, E.

Shaughnessy, A.

Turner, D.

English

NASA Technical Reports Server

Individual Recognition 
Between Mother and Infant Bats 
(My 0 tis) 
DENNIS TURNER 
ANNA SHAUGHNESSY 
EDWIN GQULD 
The Johns Hopkins University 
NDIVIDUAL RECOGNITION AMONG BIRDS has I received a great deal of attention (refs. 1 
to 6) ,  while among mammals the literature 
on this subject is relatively sparse. Marler 
(ref. 7)  noted individual differences in a typ- 
ical call pattern of wild chimpanzees. Bartho- 
lomew (ref. 8) described individual recogni- 
tion between mother and infant Alaskan fur 
seals. Bowers and Alexander (ref. 9) demon- 
strated that olfactory cues were used by labo- 
ratory mice to discriminate between individu- 
als, Human mothers can identify their own 
infant’s hunger cry from those of other in- 
fants (ref. 10). 
Individual recognition is ultimately based 
on some form of communication; visual, ol- 
factory, auditory, tactile and/or gustatory sti- 
muli provide the cues for identification. Ani- 
mals tend to emphasize one avenue of com- 
munication more than others, and the kinds 
of stimuli utilized depend on the habitat and 
mode of life of the species (ref. 11). Thus 
with the nocturnal bats, one .might expect 
auditory and/or olfactory stimuli to take pre- 
cedence over visual cues. In  the few genera 
of bats that have been studied, the mother 
selectively nurses only her own young, i.e., 
Eptesicus (ref. 22), Pteropus (ref. 13), Nycti- 
ceius (ref. 14), and Tadarida (ref. 15). 
Selective nursing implies individual recogni- 
tion. Mohres (ref. 16) and Kulzer (ref. 15) 
have suggested that bat ultrasonics may func- 
tion in communicating as well as sensing. 
Several authors have described the continu- 
ous nature of calls emitted by infant bats and 
concluded that they serve to attract the 
mother to the infant (refs. 12, 14, 15, 17, and 
18). Ncvick (ref. 19) has suggested that the 
diverse echolocation sounds in different spe- 
cies of bats may be correlates of different 
sonar systems. But these differences in dura- 
tion, intensity, and frequency could also con- 
tribute to the uniqueness of the sounds as 
communicative signals. Marler and Hamilton 
(ref. 20) and Mohres (ref. 16) suggest that 
the pulse characteristics could serve as a cue 
for localization by the mother. Individual 
recognition based on auditory stimuli could 
prove very useful to the bat. When the 
mother returns to the nursery colony after 
her daily feeding excursion, she must locate 
her own infant. The colony is increasing in 
365 
https://ntrs.nasa.gov/search.jsp?R=19720017435 2020-03-17T03:52:03+00:00Z
366 A N I M A L  O R I E N T A T I O N  A N D  N A V I G A T I O N  
FIGURE 1. Diagram of Y maze apparatus. 
numbers daily, and her infant becomes more 
mobile with maturation. There is evidence1 
that the infant’s voice characteristics change 
as it grows, and this may provide the individ- 
uality necessary for recognition. This remains 
to be seen. In  this paper, the authors have 
attempted to determine whether individual 
recognition occurs in the little brown bat 
(Myotis lucifugus) , and if so, what the basis 
for that recognition is. 
METHODS 
Mother-infant pairs of Myotis lucifugus 
were captured from Baltimore nursery colo- 
nies and brought into the laboratory in June 
1970. When captured, infants ranged from 1 
to approximately 4 days old. Cornel1 mos- 
quito cages, 30Yz cm3, contained the bats in 
a room held at 32” C. with circulating air. 
Humidity was maintained by placing several 
large evaporation trays on the floor. The bats 
were fed and watered once a day but other- 
wise disturbed as little as possible. Bats were 
identified by bands and toe clips. For other 
details on care and feeding, see Gould.’ 
The experiments were conducted in a sec- 
ond room, kept at the same temperature and 
GOULD, E.: Studies of Maternal-Infant Com- 
munication and Development of Vocalizations in 
the Bats Myotis and Eptesicus. Commun. Behav. 
Biol. (in press). 
removed from the animal room by still a 
third room. An aluminum sided Y maze was 
used to test the ability of the infant to recog- 
nize its mother on the basis of auditory com- 
munication [fig. 1). Each arm of the maze 
measured 65 X 14 x 17 cm. The top of 
each arm was covered by a sliding Plexiglas 
sheet. Guarded fans (10 cm diam), which 
moved 50 cfm/fan, were placed on two arms 
of the Y to draw air out of the chamber. The 
maze was positioned so that varying condi- 
tions in the room, such as overhead lights, 
would be accounted for. 
Two mothers were separated from their 
infants and each one randomly placed in a 
holding box, 17 x 10 X 12.5 cm, at the end 
of an arm, These cardboard holding boxes 
had double screening on the end facing the 
junction of the maze; fine screen was used to 
eliminate the use of vision by the infant. The 
opposite end of the box had a single layer to 
allow the air to be drawn out of the cham- 
ber. The infant to be tested was placed under 
a %-in. hardware cloth cover at the junction 
of the arms where its mother and an alien 
mother were located. The alien mother’s in- 
fant was removed to the animal room. After 
a 10-min waiting period, the cover on the test 
aqimal was gently lifted and the infant’s 
movement recorded. This waiting period was 
designed to allow ample time for the infant 
to calm down and for communication be- 
tween the bats to occur. A point 35 cm down 
each arm was arbitrarily taken to be the 
“choice” point, although in every case, the 
infant went all the way to a box holding an 
adult. 
Between each run, papers were laid down 
to minimize the possible effect of a scent 
trail. Several infants were used more than 
once, but only after a minimum 72-hr inter- 
val between runs, In all cases, the adults were 
randomly placed at the maze arms. However, 
it should be noted that when the alien moth- 
S E S S I O N  V: S E N S O R Y  M E C H A N I S M S - M E C H A N I C A L  367 
er's infant was tested, the random placing of 
the two mothers was sometimes such that 
their positions remained the same as when 
the first infant was tested. 
Twenty runs were completed in this man- 
ner using 13 mother-infant pairs. The last 
nine runs were recorded at 30 ips using a 
Precision Instrument Tape Recorder No. 
202, modified Granath ultrasonic microphone 
system, to test whether the bats were emitting 
ultrasonic communication signals. The recor- 
der was turned on after the adults were in 
position and just before the door was opened 
to permit entry with the infant to be tested. 
Later, the recordings were slowed 16 times, 
played through a Tektronix Type 503 Oscil- 
loscope, and filmed with a 35 mm Kymo- 
graph Camera Model C&K. The communi- 
cation signals were first described by Gould? 
who listened to the slowed sounds of isolated 
infants and isolated adult mothers. He was 
able to distinguish the mother and infant 
when they called simultaneously on the same 
tape, and his description of the vocalizations 
was used in this experiment. The total num- 
ber of antiphonal chirps from each mother 
was tabulated. Isolation call-antiphonal chirp 
pairs were randomly selected from the tapes 
and filmed for duration analysis. A standard- 
ized technique was used to measure the 
length of the i call, and then the span from 
the end of the i call to the beginning of the A 
chirp. The interval from the beginning of the 
i call to the beginning of the A chirp was also 
measured. 
TABLE 1.-Results of the Y Maze Test 
and the alien mothers five times. Isolation 
calls were emitted by infants during all of the 
nine recorded runs, but mothers answered 
these vocalizations with antiphonal chirps in 
only eight runs. One notes from table 2 that 
ultrasonic communication occurred during 
several runs in which the infant made an 
incorrect choice. Also, there were no anti- 
phonal chirps emitted during run number 15, 
an incorrect choice. 
From this experiment, the authors have 
concluded that individual recognition be- 
tween mother and infant did occur. How- 
ever, it cannot be determined at this time if 
the recognition was based on ultrasonic com- 
munication or olfactory stimuli. The infant 
was prohibited from receiving odors of either 
adult, yet it is possible that the mother recog- 
RESULTS AND DISCUSSION 
It  can be seen from table 1 that infants 
chose their own mothers in 15 of the runs 
'GOULD, E.: Studies of Maternal-Infant Corn- 
munication and Development of Vocalizations in 
the Bats Myotis and Eptesicus. Commun. Behav. 
Biol. (in press). 
nized the odor of her infant in the air being 
drawn past her. she may have then "led in 
response to the olfactory stimuli and/or the 
368 A N I M A L  O R I E N T A T I O N  A N D  N A V I G A T I O N  
I I 
I 
TABLE 2.-Analysis of Recorded Runs 
23 
13 
7 
12 
17 
9 
23 
5 
15 
i calls 
yes. . . . . . . . . . . . .  
yes. ............ 
yes.. ........... 
yes. ............ 
yes. . . . . . . . . . . . .  
yes ............. 
yes. . . . . . . . . . . . .  
yes . . . . . . . . . . . . .  
yes. ............ 
12’ 
13 
14 
15 
16 
17 
18 
19 
20 
I I 
A chirps Number 
A chirps 
96 
388 
106 
none 
7 
8 
7 
115 
654 
Choice 
yes. ............. 
yes. ............. 
yes. ............. 
no ............... 
yes. ............. 
yes. ............. 
yes. ............. 
yes . . . . . . . . . . . . . .  
yes. . . . . . . . . . . . . .  
2 XMother 
1 X Alien 
Mother 
Mother 
Alien 
Alien 
Mother 
Mother 
Alien 
Mother 
e Twice during this run, the infant pushed the hardware cloth cover toward the mother’s arm of the maze. 
When released after 10 min., the infant chose the alien mother. 
infant’s isolation calls; and the infant, in 
turn, chose the only arm of the Y maze carry- 
ing auditory stimuli. However, it is significant 
that the infant responded to the mother’s vo- 
calizations. As for the five incorrect choices, 
it is possible that the system is only 75-per- 
cent efficient. At this time, we are unable to 
determine whether one or both adult mothers 
responded to the infant calls. Several of the 
incorrect choices were made in unrecorded 
runs and may or may not have involved anti- 
phonal calling by the mother. 
If the basis for recognition is ultrasonic 
vocalization, one must assume that there is 
sufficient variability in individual calls and 
that this variability is utilized by the bat. 
Bateson (ref. 21) in discussing dolphin vocal- 
ization suggests that we will not know much 
about the communication process until we 
know what one dolphin reads in another dol- 
phin’s signals. The same holds for bat com- 
munication. The literature on the individual- 
ity of bat vocalizations is sparse, but the au- 
thors have found statistical differences (99- 
percent level of significance, parametric anal- 
ysis of variance) between the different moth- 
er-infant pairs in the duration of an infant’s i 
call, the interval from the end of the i call to 
the beginning of the A chirp, and the inter- 
val from the beginning of the i call to the 
beginning of the A chirp. 
Overlaps occur between i call durations of 
different infants (fig. 2 )  and between inter- 
vals of different mother-infant pairs (figs. 3 
and 4). One might argue that because of 
these overlaps, i call duration would be a 
poor substrate for individual recognition. 
However, in a large nursery colony, any clue 
might help the mother locate her infant. Per- 
haps at least a portion of the population 
could be eliminated by hearing i calls of 
vastly different duration than those of her 
own infant. Final recognition may be based 
on olfactory cues as in Rousettus (ref. 22). 
There appears to be no apparent relation be- 
tween the i call duration and the age of the 
infant. Nor can any conclusions be drawn 
concerning the numbers of antiphonal chirps 
required for the infant to localize the mother. 
Since differences between mother-infant pairs 
S E S S I O N  V: SENSORY M E C H A N I S M S - M E C H A N I C A L  369 
Sag+ 
7 
I f  
I2 
6 
2f 
to 
24- 
4 
FIGURE 2. Duration of isolation call. Lower bar 
of each triplet shows range data for each infant. 
Center bar shows 2 1  standard deviation from 
the mean. Upper bar represents mean duration 
of that infant's call. 
in the interval from the end of an i call to 
beginning of the A chirp exist, it is possible 
that the infant may utilize this information 
and crawl toward the mother or modify its 
vocalizing pattern. Therefore, at least two 
possible variables in the vocalizing behavior 
of Myotis exist: i call duration and interval 
length. The use of these variables by the bat 
has not been demonstrated. Nor does this 
finding obviate the possibility that harmonics 
unique to each individual are used as a basis 
for recognition. 
SUMMARY 
Mother-infant pairs of Myotis lucifugus 
were tested for individual recognition using 
an aluminum sided Y maze. Two mothers 
were randomly placed at the ends of two of 
the arms of the maze and the infant was 
placed at the junction of these arms. The 
infant's use of vision was eliminated by plac- 
ing each mother in a holding box which had 
fine double screening on the end of the box 
facing the infant. Air was drawn out of the 
chamber past the two mothers. Twenty runs 
Interval in m.uc 
FIGURE 3. Interval from end of isolation call to 
beginniig of antiphonal chi .  Lower bar of 
each triplet shows range of intervals for each 
mother-infant pair. Center bar shows 2 1  stand- 
ard deviation from the mean. Upper bar repre- 
sents mean of the intervals. 
Sam3.k 
-6 
I 4  
1 
IO 
I.? 
21 
24 
4 
A 
A 
I, 
A 
-LI, 
-c 
.I
20 SO 4 4  50 
Interval i n  ~ I L C  
FIGURE 4. Interval from beginning of isolation 
call to beginning of antiphonal chirp. Symbols 
as in figure 3. 
were completed using 13 mother-infant pairs. 
The last nine runs were recorded for later 
analysis of communication signals. 
Infants chose their own mothers in 15 of 
the 20 runs. The authors conclude, therefore, 
that individual recognition did occur but are 
unable to determine whether recognition was 
based on auditory and/or olfactory stimuli. 
Analysis of the recorded runs shows differ- 
ences between mother-infant pairs in both 
370 A N I M A L  O R I E N T A T I O N  A N D  N A V I G A T I O N  
the duration of the infant’s isolation call and 
the interval from the end of this call to the 
beginning of the mother’s antiphonal chirp. 
Implications of these differences are dis- 
cussed. 
ACKNOWLEDGMENT 
Financial support for this research came from 
the National Institutes of Health, Grants No. 2 
ROI NBO7229-02 and 5 SOI-FR-5445-09. ’ 
DISCUSSION 
WATERMAN: The flying foxes in the Caroline 
Islands seem to have rather prominent social com- 
munication in our audio range. Do these kinds of 
bats have an echo-locating mechanism? 
GOULD: No, but Nelson (ref. 13) has indicated 
that there is antiphonal calling. He observed the 
mothers calling to their specific infants; he sug- 
gested that they were, in fact, recognizing one an- 
other. He did not conduct experiments with indi- 
vidual recognition, although Kulzer (ref. 22) 
showed that the mother could identify her infant if 
the infant was in a bag next to a strange infant in 
a bag. Nelson has described quite a number of vo- 
calizations and has shown how many of them pro- 
mote spacing in the group since there seems to be 
in some places limited roosting sites; territorial 
males are also described. 
GRIFFIN : Have you studied the communication 
calls of the adult bats? 
GOULD: Yes. Turner and Shaughnessy put 
cages a few feet apart and separated them with 
thick cotton, placing microphones so that only the 
infant sounds from a single cage were detected. I t  
was rigged with a signal operated relay and 
checked out on the event recorder to see whether 
the calling of infants and adults were related. After 
a long quiet period, the mother would call and 
then the infant would call, and this would go on 
throughout the night. They also found that this 
was true with two different infants. They tried it 
with adults that were in the colony for some time, 
and there was no such correlation. A better ap- 
proach might be to take adults that have been sep- 
arated for a period of time, where there might be a 
greater likelihood of communication, particularly 
those who are closely related or in colonies. 
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Individual recognition between mother and infant bats (Myotis)

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