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|Title: ||Variation in sperm whale (Physeter macrocephalus) coda vocalizations and social structure in the North Atlantic Ocean|
|Authors: ||Antunes, Ricardo|
|Supervisors: ||Gordon, Jonathan|
Hammond, Philip S.
|Keywords: ||Sperm whale|
|Issue Date: ||30-Nov-2009|
|Abstract: ||This study aimed at complementing studies of sperm whale social and vocal behaviour that
were restricted to the Pacific Ocean.
The characteristic multi-pulsed structure of sperm whale clicks allows for estimation of
whales' size from measurements of the inter-pulse intervals (IPI). I have developed two new
automatic methods for IPI estimation from clicks recorded during foraging dives. When compared
to other previously developed methods, the newly developed method that averages several clicks'
autocorrelation function showed the best performance amongst the automatic methods.
Previous studies did not support individual identity advertisement among social unit
members as the function for the sperm whale communication signals called codas. I tested within
coda type variation for individual specific patterns and found that, while some coda types do not
allow for individual discrimination, one did so. This variation suggests that different coda types
may have distinct functions.
Analysis of social structure in the Azores found that, similar to the Eastern Tropical Pacific,
sperm whales form long term social units of about 12 individuals. Unlike the Pacific Ocean,
Azorean social units do not form temporary groups with other units, suggesting differences in the
costs and benefits of group formation. I argue that these are due to differences in terms of predation
pressure and intraspecific competition between the Azores and the Pacific study sites.
The variation of coda repertoires in the Atlantic also showed a pattern dissimilar to that
previously documented in the Eastern Tropical Pacific. In the North Atlantic, coda repertoire
variation is mostly geographic, which is parsimoniously explained by random drift of culturally
transmitted coda repertoires. No sympatric vocal clans with distinct dialects were found as has been
noted in the Pacific. Drawing upon the differences found in social structure I argue that selection for
maximization of differences between units with similar foraging strategies may have led to the
Pacific vocal clans.
The differences between oceans suggest that sperm whales may adaptively adjust their
behaviour according to experienced ecological conditions.|
|Publisher: ||University of St Andrews|
|Appears in Collections:||Biology Theses|
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