REPRINT No. 41 from Animal Behaviour, 22, 3, August, 1974
Anim. Behav., 1974,22,656-663
DIALECTS OF NORTHERN ELEPHANT SEALS, MIROUNGA ANGUSTIROSTRIS: ORIGIN AND RELIABILITY By BURNEY J. LE BOEUF* & LEWIS F. PETRINOVICHt
*Crown College, University of California, Santa Cruz, California 95064
t Department ofPsychology, University of California, Riverside, California 92502
Abstract. Threat vocalizations of adult male northern elephant seals, Mirounga angustirostris, were
recorded over a 5-year period to determine whether local dialects previously reported in this species
are reliable. These results were obtained: (1) The mean pulse rate at Ano Nuevo Island, which was
colonized in 1961, has increased every year from 1968 to 1972 but still remains slower than the mean
pulse rate of all southern rookeries. (2) The pulse rate of individual adult males does not vary significant­
ly for at least 3 years. (3) Forty-three per cent of the breeding males on Ano Nuevo Island are immi­
grants from southern populations each of which has a faster mean pulse rate than Ano Nuevo Island.
(4) The pulse rate at San Miguel Island, a large rookery which receives few immigrants, did not change
significantly from 1969 to 1972. A model is advanced to explain the data and account for geographical
variation in learned vocalizations of species whose populations are expanding.
mechanisms reducing gene flow between neigh­
bouring populations (Thielcke 1969; Nottebohm
1969, 1972). Regional dialects in white-crowned
sparrows are stable over a period of at least 4
years (L. Baptista, personal communication).
According to Thielcke (1969), constancy of
dialects over several years has also been demon­
strated in the short-toed treecreeper, Certhia
brachydactyla, and in the chaffinch. Marler
(1970) discusses how labile learned dialects
could continue to affect gene flow.
The term dialect refers to consistent differences
in the predominant song or call of adults from
different populations of the same species (Marler
& Tamura 1962). Dialects are a behavioural
expression of intraspecific geographic variation
and they have been identified in several birds,
a seal and man. Whether the phenomenon is
analogous in these species is open to question.
Nevertheless, the concept has been especially
useful in describing geographic variation in
vocalizations of the chaffinch, Fringilla coelebs
(Thorpe 1961), the white-crowned sparrow,
Zonotrichia /eucophrys nuttalli (Marler & Tamura
1962, 1964) and a few other passerines (e.g.
Lemon 1966; Nottebohm 1969; Thielcke 1969).
The only non-human mammal in which
dialects have been described is the northern
elephant seal, M. angustirostris. Le Boeuf &
Peterson (1969a) found that the mean pulse
rates of male threat-vocalizations on San Miguel
Island and Isla de Guadalupe were quite similar
(1'88 and 1·88 pulse per second, respectively),
but the mean pulse rate for males from San
Nicolas Island was much higher (2'53 pulse
per second) and was a good deal lower for males
from Ano Nuevo Island (1·02 pulse per second).
Additional variants differentiating the breeding
populations were described.
The purpose of this paper is to examine the
reliability of elephant seal dialects over a 5-year
period, particularly the dialect of one rookery.
This is important because the concept of dialects
implies consistency over the years. Lacking this
consistency, any presumed functional signifi­
cance of dialects would be questionable, par­
ticularly the notion that they serve as isolating
Northern elephant seals offer several advan­
tages for the study of geographic variation in
vocalizations. The history of the species since
its near extinction in the last century has been
documented, and the speed of dialect formation
can be estimated, for we know when the rook­
eries were re-colonized. Individuals can be
marked and studied for several years. Since
breeding occurs on islands, breeding populations
are disparate and easily distinguishable from
each other. Tagging studies facilitate the study
of dispersion, recruitment and other population
variables which might affect the reliability of
dialects.
Background Information
Before nineteenth-century sealers began to
exploit northern elephant seals for blubber,
their breeding range was from Cabo San
Lazaro in Baja California, Mexico, to the
Point Reyes peninsula north of San Francisco,
California (Scammon 1874). By 1892, the entire
population had been reduced to a herd of less
than 100 animals which lived on remote Isla
de Guadalupe (Fig. 1), 243 km west of Baja
656
657
LE BOEUF & PETRINOVICH: DIALECTS OF NORTHERN ELEPHANT SEALS
California (Bartholomew & Hubbs 1960). The
30 000 or more northern elephant seals which
exist today (Peterson & Le Boeuf 1969) are
descendants of this remnant herd.
With time, and the protection afforded by the
Mexican and United States governments, the
Guadalupe population grew, and re-colonization
of former breeding locations occurred. The
time and place that breeding commenced on
some of these islands was as follows: San Miguel
Island (ca. 1938), Islas San Benito (ca. 1948),
San Nicolas Island (ca. 1950), Ano Nuevo Island
(1961), and Southeast Farallon Island (1972)
(Bartholomew & Hubbs 1960; Radford, Orr &
Hubbs 1965; Le Boeuf, Ainley & Lewis 1974).
Therefore, the local dialects evident in the four
rookeries examined in 1968 (Le Boeuf &
Peterson 1969a) were due either to differences
that had developed very quickly (7, 18 and 30
years or less for Ano Nuevo, San Nicolas, and
San Miguel Islands, respectively) or to dif­
ferences evident from the time the colonies were
established. The oldest recolonized rookery,
San Miguel Island, had a dialect indistinguish­
able from the Isla de Guadalupe popUlation in
1968-69.
In 1972, the largest elephant seal rookery was
stilI Isla de Guadalupe, with approximately 6200
breeding females. From censuses taken during
the last 5 years (Le Boeuf, unpublished data)
the number of females on other major rookeries
was estimated as follows: San Miguel Island
(2200), Islas San Benito (2200), San Nicolas
Island (600), Isla Cedros (63), and Ano Nuevo
Island (400). The population on all of these
islands is increasing and the breeding range
is stilI expanding. Breeding was most recently
re-established on Southeast Farallon Island
where two females were sighted during the
1972 breeding season and one pup was born
(Le Boeuf et al. 1974).
Beginning in 1968, Le Boeuf and colleagues
, from the University of California at Santa Cruz
began tagging elephant seals on several major
rookeries where elephant seals were known to
breed (Fig. 1). Approximately 90 per cent of the
seals tagged were I-month-old, newly weaned
pups. By June 1972, it was clear that dispersion
from the island of birth was considerable during
the first 5 years of life (Le Boeuf 1971; Le Boeuf
et al. 1974).
All observations of tagged seals occurred
north of their birthplace, with the exception of
some Gualalupe-born seals which were sighted
on Islas San Benito to the east. Pups born and
I
I
FARALLON
IS
A O NUEVO
SAN
. •
I.·
{\
I
I
I
I
I
I
FRANCISCO \
\
'\
\
l--
CALIFORNIA\
\
SAN NICOLAS I
.
•
('I
I.
DE GUADAlUPE ,
1Z.
IS. SAN BENITO "
I. CEDROS
,
)
_
Fig. 1. Breeding locations of the northern elephant seal.
This species also breeds on Los Coronados and Santa
Barbara Island (not shown).
tagged on Isla de Guadalupe a nd on Islas San
Benito have also been ob served on San Miguel
Island and on San Nicolas Island. Seals origin­
ating from Baja California islands have not been
observed on Ano Nuevo Island nor on Southeast
Farallon Island. However, numerous seals have
been sighted on the latter islands which were
born on San Miguel Island and a small number
from San Nicolas Island. Southward move­
ments, or movements from Islas San Benito to
Isla de Guadalupe, have not been observed.
The majority of tagged animals sighted were
between 9 and 16!months of age and most of
them were observed in the new area throughout
the first 4 years of life. Few of these animals
were ever seen again on the rookery of their
birthplace (Le Boeuf et al. 1974). Therefore, it
seems that the northward movement is permanent.
Little dispersion has been observed after the
5th or 6th year of life, the age when most animals
of both sexes have undergone puberty. That is,
once a male or female was observed on a rookery
"
ANIMAL
BEHAVIOUR,
during the breeding season, it returned to that
same rookery to breed in subsequent years.
Methods
Tape recordings of adult male threat vocali­
zations were made during the breedingseasons,
1968 through 1972, on Ano Nuevo Island and
on San Miguel Island during the same period
with the exception of 1970. Tapes were recorded
at 71 i.p.s. using a Uher Report L, a Nagra III
or a Nagra IV tape recorder with a Uher M514
microphone or a Sennheiser MKH 805 direct­
ional microphone. The overall frequency re­
sponse of the system was from at least 70 to
14000 Hz. Sonograms of male threat vocaliz­
ations can be found in Bartholomew & Collias
(1962) and Le Boeuf & Peterson (1969a).
Only complete recordings of spontaneous
vocalizations by adult males were used. In the
Ano Nuevo sample, all subjects were positively
identified on the tape recordings. This was
possible because all resident males were in­
dividually marked. At San Miguel Island we
avoided inadvertently sampling the same male
twice in one season by recording the entire
sample on a single pass along the periphery of
the western tip of the rookery. This could be
done in approximately 3 he The sampling
locations on both islands, dictated by the
restricted areas used for breeding, offered us the
potential of recording all adult males in resid­
ence. These circumstances, plus the precautions
we took, and the fact thatinclusion in the sample
was ultimately determined by whethera potential
subject was vocally threatening another male
when we were in recording range, makes us
confident that our sampling was done randomly
and represents the breeding population from
which it was taken.
The recordings were analysed on a Kay
7029A Sound Spectrograph, and spectrograms
22,
658
3
were measured to determine the time in seconds
between the beginning of the first and the
beginning of the last pulse in a burst, the
number of pulses, the pulse rate (PR), the
duration of the longest pulse, and the funda­
mental frequency. Other variants such as un­
usually prolonged pulses, long pauses between
pulses, and terminal flourishes were noted.
Summary statistics were obtained for each
animal and these statistics were used to charac­
terize the vocalizations.
Results
Aiio Nuevo Island. The data presented in
Table I are based on a random selection of a
single vocal burst from each of seventeen to
twenty-six adult males on Ano Nuevo Island
during five breeding seasons. Except for mean
PR and the linked measures, burst duration and
number of pulses in a burst, the other two
measures, pulse duration and fundamental
frequency, were unreliable across individuals.
Mean PR, the best measure of dialects in
elephant seals, showed systematic and significant
changes over the years. The PR increased
steadily from a mean of 0·97 pulse per second
in 1968 to a mean of 1·47 pulse per second in
1972. Using the data for only 1 year for each
animal, a one-way analysis of variance was
computed and the mean difference is significant
(F 29'8, df 4·84, P<0·05). The variability
around the mean value also increased as in­
dicated by an increase in the size of the SD
from 0·06 in 1968 to 0·17 in 1972. The increase
in size of the SD occurred more rapidly than did
the increase in the value of the mean; the SD
more than doubled from 1968 to 1969. We
have, therefore, a gradual dialect drift as indexed
by PR, and this dialect drift is accompanied by
a rapid initial increase in variability. It appears
=
=
Table I. Parameters of Adult Male Vocalizations at Aiio Nuevo Island Over a 5-year Period (Means and SD)
I;
Fundamental
frequency
Pulse rate
( pulse/s)
Burst duration
Year
Sample
size
(no.)
1968
26
0·97 ± 0·06
5·72 ± 1·40
5·60 ± 1·30
0'51 ± 0·12
334 ± 174
1969
23
HO ± 0·14
6·18
6·60
± 2·00
0'38 ± 0·11
168 ±
1970
17
1·22 ± 0·19
4·93 ± 1·62
5·88 ± 1·78
0·29 ± 0·13
176 ± 124
197 1
22
1'39±0'19
6'27 ± 1·84
± 2·63
0'32 ± 0'13
178 ±
33
1972
19
1·47 ± 0·17
6·75 ± 2·61
9·68 ± 3'28
0·30 ± 0·09
202 ±
54
(s)
± 2'60
Pulses per burst
(no.)
8·64
Pulse duration
(s)
(Hz)
58
659
LE BOEUF & PETRINOVICH: DIALECTS OF NORTHERN ELEPHANT SEALS
Table n. Mean Pulse Rates of Adult Male Elephant Seals
at Aiio Neuvo Island from Year to Year
Male
1968
1969
1970
OL
1·00
1·04
1-06
GLS
1-07
1·05
1'16
QSN
1-46
1·53
1·28
GA
1·09
1·12
1·18
PIN
1-06
1971
1972
1·04
NOT
1·17
GON
1 ·47
1-17
1·33
RAT
1·14
1-16
1·13
CAL
1·56
1·56
1·47
OB
1·25
1'29
604
1·46
1·45
SAM
1·31
1·38
II collected in two to three breeding seasons
from twelve adult males indicate that this
interpretation is incorrect; the PRs of these
individuals did not change significantly over a
3-year period, the longest interval for which we
have vocalizations on marked individuals. There­
fore, we reject the hypothesis that the systematic
increase in the mean PR for the Ano Nuevo
Island population was due to a systematic
increase in PRs of individual bulls in residence.
Finally, the dialect drift could have resulted
from males immigrating from southern rookeries
emitting faster PRs which elevated the mean PR
of the Ano Nuevo population and increased the
standard deviation. First of all, the mean PRs
for all rookeries examined by Le Boeuf &
Peterson (l969a) were faster than the mean PR
found at Ano Nuevo Island in 1972 (1-47 pulse
per second). The slowest mean PR of rookeries
south of Ano Nuevo Island was that of males at
Isla de Guadalupe (1'77 ± 0·39 pulse per
second). The mean PR of the previously un­
described San Benito popUlation, 2·17 ± 0·90
49), was also faster than the Ano
in 1970 (N
Nuevo mean (Le Boeuf, unpublished observa­
tions).
Males have clearly immigrated from southern
rookeries to Ano Nuevo Island since the popu­
lation has been expanding, and breeding only
began at Ano Nuevo since 1961. Virtually all
of the breeding males at Ano Nuevo Island
from 1961 to 1971 had to be recruited from
southern populations. Even in the most recent
years, males born at Ano Nuevo Island formed
only a small part of the resident male breeding
population. That is, despite the fact that nearly
all pups born on Ano Nuevo Island from 1961
to 1967 (approximately 359) were tagged by
Stanford Research Institute researchers (Poulter
& Jennings, Annual Reports to the Division of
Beaches and Parks, State of California, 1962 to
1966; Orr & Poulter 1965), relatively few of these
animals Were seen there from 1968 to 1972
(Le Boeuf 1974). Twelve of these 5- to 8-year-old
natives were present during the 1971 breeding
season and fifteen were present in 1972; the
total number of males present in each of these
seasons was 136 and 146, respectively. Moreover,
these natives were still not full grown adults in
1972. Although males undergo puberty at
approximately 5 to 6 years of age, most of
them do not compete successfully for females
until they are full grown, at about ten years of
age (Le Boeuf & Peterson 1969b; Le Boeuf 1974).
In 1971 and 1972, we made a special effort
=
that this mean PR is approaching that of San
Miguel Island and Isla de Guadalupe, that is to
say approximately 1·8 pulse per second (Le
Boeuf & Peterson 1969a).
We will consider four alternative explanations
for the observed drift in the mean PR of Ano
Nuevo Island. The observed change in PR might
have been produced by changes in the size or
density of the Ano Nuevo population. We have
already mentioned that this population increased
steadily over the years 1968 to 1972 (Le Boeuf
et al. 1974; Le Boeuf 1974). This interpretation
is not feasible since the rookery at San Nicolas
Island was of comparable size and density to
that at Ano Nuevo Island in 1968 to 1969 and
its PR was extremely rapid (2'53 pulse per
second) at the outset while that at Ano Nuevo
Island was extremely slow (0'97 pulse per second).
Another possible interpretation is that the
change in mean PR might have resulted from
changes in local environmental factors, what
Marler & Hamilton (1966) call the sound
environment. It is difficult to rule out this
possibility but we know of no environmental
changes that occurred between 1968 and 1972
which could account for the steady increment
in mean PRo
The observed drift in PR might have been the
result of the PRs of individual males becoming
more rapid with maturation. The data in Table
ANIMAL
BEHAVIOUR,
22,
3
660
Table ill. Parameters of Native and Immigrant Sub-Adult Male Vocalizations at Ano Nuevo Island in 1971 and 1972
Sample
size
(no.)
Natives
Immigrants
Pulse rate
(pulse/s)
Pulse duration
(s)
Fundamental
frequency
(Hz)
1971
1972
7
7
1·49 ±0·16
1·42±0·14
0·29 ±0·15
147 ±27
213 ±53
1971
1972
5
10
1·46 ±0·10
1·54±0·14
0·32 ± 0·06
0·26 ±0·10
175 ± 30
203 ± 34
to estimate the number and age of immigrants
to the Ano Nuevo rookery. Immigrants were
distinguished by the absence of a tag or tag
scar since all Ano Nuevo born animals were
tagged within It months after birth. In both
years 43 per cent of the total males in residence
were new immigrants, that is to say they had
not been born on Ano Nuevo Island nor tagged
there in previous years. In 1971, 85 per cent of
the immigrants were estimated to be between
5 and 8 years of age; 98 per cent were estimated
to be in this age interval in 1972. In both years,
the majority of immigrants were 5 to 6 years of
age. We are confident about our age estimates
since we had constant reference to marked
animals of known age (Le Boeuf 1974). There­
fore, it is clear that most immigrants to Ano
Nuevo Island are less than 8 years old when they
first arrive. Of course, many animals immigrate
much earlier, some of them during the first year
of life. These may remain associated with the
new location as juveniles until they reach
pUberty. Once a pubertal male appears on a
rookery for his first breeding season he returns
to that same rookery in subsequent breeding
seasons (Le Boeuf 1974).
What was the PR of 5- to 8-year-old immi­
grants to Ano Nuevo Island? Five males re­
corded in 1971 had a mean PR of 1 4 6 ± 0·10.
Ten males in 1972 had a PR of 1·54±0·14.
Both means are only slightly higher than the
population means during each respective year
(Table I). Recordings made on three males in
both seasons indicated there was no consistent
change in PR from one season to the next:
1·42 to 1·56, 1·33 to 1·25, and 1·46 to 1·45.
Therefore, these data indicate that the mean
PR of this class of immigrants is very close to
that characterizing the population mean, and
there is preliminary evidence that the PR of
these immigrants is stable over the years.
-
A comparison of the above immigrants
with natives in the same age category reveals no
0·29 ± 0·08
differences in PR, pulse duration, nor funda­
mental frequency (Table III). Recordings ob­
tained from four natives during 1971 and 1972
reveal that three of them showed slightly lower
PRs in the second year. The mean PR for these
four males was 1·55 pulse per second in 1971
and 1·40 pulse per second in 1972. With this
small number of cases it is not meaningful to
apply a statistical test.
Might PRs of natives depend on where they
developed and to what PRs they were exposed?
That is, would males born in 1961 and recorded
in 1968 emit slower PRs than those born in
1965 and recorded in 1972? Unfortunately, we
have little data bearing on this point. Our frag­
mentary results suggest no differences. In 1972,
three 8-year-old males had pulse rates of 1·63,
1·38 and 1·15; three 7-year-olds had pulse rates
of 1·27, 1·56 and 1·31, and one 6-year-old
had a pulse rate of 1·63.
San Miguel Island. Does dialect drift occur
on other rookeries? In particular, those with a
large popUlation which receive few immigrants?
Data concerning this question were obtained
from recordings made on San Miguel Island
during four breeding seasons over a span of 5
years. The PRs shown in Table IV indicate a
significant drop from 1968 to 1969 (t
2·83,
df
31, P
<0·05) followed by a very stable
PR over the next 4 years. The small sample
taken in 1968 may in part account for the
elevated figure for that year.
=
=
=
Consistent with the immigration hypothesis
is the fact that among all the rookeries, the PR
that is most similar to that of the founder
colony, Isla de Guadalupe, is found at San
Miguel Island. San Miguel Island initially
received immigrants from Isla de Guadalupe
and is currently the largest and oldest re­
established rookery. The immigration hypothesis
predicts that the mean PR for San Miguel
Island would approach that of the founder
LE BOEUF & PETRINOVICH: DIALECTS OF NORTHERN ELEPHANT SEALS
661
Table IV. Pulse Rates of Adult Male Elephant Seals at
San Miguel Island (Means and SD)
Year
Sample size
(no.)
Pulse rate
(pulse/s)
1968
13
2'11 ± 0·36
1969
20
1·75 ± 0·35
1971
28
1·74 ± 0·49
46
1·70 ± 0·44
1972
colony as the San Miguel colony grew, app­
roached stability, and immigration from Isla de
Guadalupe became negligible.
Other measures. Time and space limitations
permit only a brief mention of other variables
which vary across populations. During 1968 and
1969, Le Boeuf& Peterson (1969a) reported
that males from Ano Nuevo Island never pro­
longed the initial or terminal pulse in a burst of
pulses, a characteristic common to a certain
proportion of males from all other· rookeries
sampled. For example, of twenty-eight males
from San Miguel Island sampled in 1971, 15
per cent prolonged the initial pulse and 75 per
cent prolonged the terminal pulse. Of forty­
nine males sampled on Islas San Benito in 1970,
47 per cent prolonged the first pulse and 43 per
cent prolonged the last pulse. Prolongation of
either the first or last pulse in a burst was not
observed in Ano Nuevo males until the 1971
breeding season. In both 1971 and 1972 fewer
than 5 per cent of the males in residence pro­
longed the initial pulse and approximately 2 per
cent of the males prolonged the terminal pulse.
Only a few males at Ano Nuevo Island ever
exhibited a slight pause between the first and
second pulses, a common characteristic on
southern rookeries, particularly San Nicolas
Island.
Pronounced differences remain between Ano
Nuevo Is1and males and those from southern
rookeries with respect to these vocal variants
just described. The intra-individual reliability
of these characteristics is high. Additional re­
search is necessary to determine the importance.
of these variables.
Discussion
The following conclusions are supported by this
study: (1) The mean PR at Ano Nuevo Island
has been increasing from year to year. (2) The
PR of individuals does not vary systematically
from year to year. .(3) There is aJarge number of
immigrants to Ano Nuevo Island each year and
the immigrants are from southern populations,
all of which have faster mean PRs than that
found at Ano Nuevo Island. (4) The PR at a
large rookery which receives few immigrants,
San Miguel Island, has remained relatively
constant over a 4-year period, following a
decrease from 1968 to 1969.
The following model speculates on the origin
of elephant seal dialects and attempts to provide
a rational construction consonant with the
systematic changes in vocalizations in space and
time reported in the present study. First, we
assume that the original male settler(s) on Ano
Nuevo Island in the early 1960s were recruited
from the low end of the PR distribution of males
from Isla de Guadalupe, the parent population.
The PR of this first male was
1·0 pulse per
second. This was due to chance sampling from a
large population that was normally distributed
with a mean PR of approximately 1·80 pulse
per second (the value observed in 1969, see Le
Boeuf& Peterson 1969a).
The annual increase in the mean PR at Ano
Nuevo Island from 1968 to 1972 was brought
about by immigration of males with higher PRs
into the population. (Annual immigration of
males into the Ano Nuevo Island population has
been factually demonstrated. All immigrants
were of southern origin where the mean PR of
rookeries is faster than that at Ano Nuevo
Island).
Young males acquire their characteristic adult
PR by entraining to the PRs of adult males to
which they are exposed throughout development.
By the time puberty is reached, the individual's
PR has stabilized or crystallized. This means that
immigrants may entrain to males at their birth­
place or at any of several rookeries they may
frequent during development. Furthermore, they
may entrain to the PR of males at the rookery to
which they immigrate and eventually settle.
This interpretation is supported by the fact that
none of the males on Ano Nuevo Island ex­
hibited the faster PRs (above 2·00 pulse per
second) found at Isla de Guadalupe and other
southern rookeries. These faster PRs would be
expected if the observed effects were the result
of regression toward the mean produced by
chance sampling differences alone.
It follows from the above that the mean PR
at Ano Nuevo Island and other deviant peri­
pheral colonies should continue to regress to
the mean PR of the founder population as long
ANIMAL
BEHAVIOUR,
as the latter population continues to expand and
immigration to the peripheral colonies con­
tinues. With time and continued immigration,
the differences or dialects between the founder
colony and peripheral colonies should decrease
and eventually disappear. If the population of
the peripheral colony stabilizes and immigra­
tion ceases while local variations are still
discernable, the remaining local dialects might
come to operate as isolating mechanisms
between adjacent populations.
If this reasoning is correct, the differences
between the founder colony and peripheral
colonies such as Ano Nuevo Island and San
Nicolas Island would appear to have been
greatest when the peripheral colonies began.
We think the dialects arose as a direct conse­
quence of the manner in which the seal popu­
lation expanded and that they were a result of
isolation. The explanatory mechanisms most
often used in the bird literature is that dialects
promote or maintain isolation.
Nottebohm (1969, 1972) argues that avian
dialects might reduce gene flow between adjacent
populations if one assumes that female birds
develop a preference for the song dialect of the
area where they are born, and that this preference
is revealed in their choice of partner. In addition,
males must learn to sing the dialects of their
birthplace and both sexes must return to breed
in the same general area where they were raised.
In this way, the dialect would also be per­
petuated.
It is unlikely that the dialects observed in the
northern elephant seal function to maintain
population integrity in this manner in view of
the pronounced immigration of juveniles taking
place. Upon reaching maturity these animals
become part of a different breeding population
from that in which they originated. Furthermore,
female elephant seals in oestrus exert no choice
between males (Le Boeuf 1972). Our data
emphasize the importance of determining whet­
her the populations under study are stable or
expanding. This is important because the
significance of dialects for any species may
rest on this distinction. This type of information
has been presented rarely in previous studies.
Acknowledgments
We thank Ron Whiting and Judy Totman for
field and laboratory assistance, Dr Carl L.
Hubbs and Don M. Robinson for transportation
to southern Californian and Mexican seal
rookeries, and Ross Lein and Dr Peter Marler
22,
662
3
for comments on the manuscript. Some of the
material in this paper was presented at a sym­
posium on the Biology of the Seal, Guelph,
Ontario, Canada, 13 to 17 August 1972, and
appears in the proceedings of that conference.
This study was supported in part by National
Science Foundation grant GB-16321 to B. J.
Le Boeuf and an intramural grant from the
University of California to L. F. Petrinovich.
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(Received 9 October 1972; revised 25 April 1973;
MS. number: AI387)