Vocal Learning in Southern Elephant Seals

S. Sanvito1,2, F. Galimberti1, E.H. Miller2 1 Elephant Seal Research Group

2 Memorial University of Newfoundland

Agonistic vocalizations

• Vocalizations are present in about 70% of agonistic interactions between males

• Vocalizations settle about 50% of agonistic interactions

Acoustics of agonistic vocalizations

• Pulse trains

• High sound level (up to 120 dB)

• Low frequency (dominant frequency around 250 Hz)

• Each call made of different “syllables”

Syllables structure is independent from the frequency structure of the vocalization

This study

• Young males vocalizations are variable, mature males vocalizations are fixed

• Fixed vocalizations can be classified in vocal types shared by two or more males

• Changes in the distribution of vocal types in consecutive years are much compatible with vocal learning

• Alternative explanations are unlikely

Methods: general• Small and localized

population Sea Lion Island, Falkland Islands

• 8 breeding seasons September to December 1995-2002

• Individual recognition of males Tags and dye marks

Methods: acoustics• Recording of vocalizations

(standard solicitation)

- 2380 vocalizations from 284 males (3 to 16 years old)

- Some males recorded in more than one breeding season (1-6)

- 29 males followed throughout their entire vocal development

• Classification in vocal types by visual inspection of waveforms- Temporal patterning of syllables

• 23 acoustic variables used to validate the visual classification- Time- Intensity- Frequency

Variable vs fixed vocalizations• Young males have variable

vocalizations i.e., the syllables pattern varies in different calls

• Mature males have fixed vocalizations i.e., each male emits always the same syllables pattern

• Percentage of males with variable vocalizations decreases with age

• Vocalizations of mature males have a high repeatability of syllable features (mean = 0.84)

Vocal types: description• Some males share the

same syllables pattern

• Some males show a unique (not shared) syllables pattern

• Males which share the same syllables pattern are classified in the same vocal type

6 vocal types recognized in this study

Vocal types: validation• Reliability of visual

classification in a blind test = 100%

• Significant differences in acoustics of vocal types (non parametric MANOVA: p = 0.0001)

• Good results in classification by canonical discriminant function (mean = 82.1% correct)

Acoustic environment• Young males listen to vocalizations of mature males

mainly (or only) during the breeding season

• Harem holders vocalizations are the main component of acoustic habitat of young males:- Holders settle contest with peripheral males using

vocalizations in 56% of cases- In 76.2% of the interactions in which a vocal component is

present, a harem holder is vocalizing- In the interactions involving a harem holding male, it

vocalizes in 75.5% of cases

• Large harems have more associated (often young) peripheral males (rho = 0.729, n = 68 harems)

General hypothesisNew unique voc alization A 1

Young males hear A

Male survive and bec ame holder

A spreads in the pop

Young males imitate A

5

A keeps spreading in the pop

Some of the "imitators" bec ome holderhenc e are further imitated

10

A dec reases in the pop

Original male plus some "imitators" dieNo new "imitators" bec ome holder

5

A disappears from the pop

All remaining males with A voc alizationsdie without bec oming holder

0

• Young males imitate harem holders vocal type

• The distribution of vocal types in the population depends on the survival and breeding status of mature males

Time

N o

f m

ales

wit

h A

voc

Changes in vocal types frequencies

• Frequencies of vocal types were not homogeneous among years (2 = 184.2; p10k = 0.0001)

1995 1996 1997 1998 1999 2000 2001 20020

5

10

15

20

25

30

35

40

Co

un

t

Year

D

C

CS

P

R

RS

• Only 2 vocal types, out of 6, were present in the first year of study

Original vocal types

• Vocal type D: bell shaped trend, it was the most common

J

J

J

J

J

JJ

J

1995 1996 1997 1998 1999 2000 2001 20020

2

4

6

8

10

12

14

16

Co

un

t o

f C

vo

cal

typ

e

Year

J J

J

J

J

J

J

J

1995 1996 1997 1998 1999 2000 2001 20020

5

10

15

20

25

30

35

40

Co

un

t o

f D

vo

cal

typ

e

Year

Original vocal types expected to be at some point of the increasing/decreasing trend

• Vocal type C: decreasing trend, almost disappeared

Spread of new vocal types• 56 males showed a fixed unique vocalization

• 4 of them became holders of large harems, with many peripherals

• These 4 males started 4 new vocal types which spread in the population, showing an increasing trend

CS P R RS

0

1

2

3

4

5

6

7

8

9

10

Co

un

t

Vocal type

• None of the unique vocalization of the remaining 52 males spread in the population

Problems and drawbacks

• Observational only, no playback: longitudinal data

• Alternatives:- inheritance of vocal types ?- repeated immigration of males sharing a

new vocal type ?

• Origin of new unique vocalizations ?

Conclusions

• Presence of vocal types

• Variation of vocal types distribution compatible with vocal learning

• Why do young males come to land during the breeding ? Acquisition of vocal competence

Thanks to the seals and to the many people that helped during the years of field work at Sea Lion Island.

Funding provided by Lerner-Gray Foundation, the University of Milano and the Italian National Council for Scientific Research.