Mutual parent-young recognition is vital for offspring survival, particularly in species congregating in dense breeding sites, like pinnipeds (seals, sea lions, and walruses). For effective vocal recognition, the caller must produce individually specific calls with high levels of stereotypy, or individuality. Vocal recognition has been studied extensively and is well-documented in otariid species (fur seals and sea lions), as those mothers frequently leave their pup to forage and must relocate them upon return to the rookery. In many phocid (true seal) species, the mothers typically remain with their pup throughout nursing and therefore may not have as strong of a need for well-developed vocal recognition; recognition remains understudied in these species. This study focuses on vocal recognition and individuality in the northern elephant seal (Mirounga angustirostris), a phocid species with a 28-day nursing period and no intentional separation between mothers and pups.
In Chapter 1, I investigated a northern elephant seal pup’s ability to vocally recognize its mother across ontogeny through an auditory playback experiment at the Piedras Blancas northern elephant seal rookery in San Simeon, CA. I found that pups showed a developed ability to recognize their mother’s vocalizations later in the nursing period, at around 23 days old. At this age, they looked towards their mother’s call faster and spent more time investigating the call. Before this age, pups responded infrequently to female vocalizations and showed no differentiated response to their own mother versus an unfamiliar female. After weaning, pups responded to any female’s call. This study is the first to examine phocid pup vocal recognition abilities, and the results suggest that northern elephant seal mothers are primarily responsible for maintaining contact during the nursing period to ensure their pup’s survival.
In Chapter 2, I analyzed and described the pup attraction calls made by adult females. Visual and auditory analysis of the spectrograms suggested there may be distinct variants of attraction calls made within and across females. I characterized the calls and confirmed that female elephant seals produce three distinct variants of their attraction call. A linear discriminant analysis correctly classified the calls into their assigned categories 80% of the time. Previous research found that female elephant seals have lower vocal stereotypy than female northern fur seals. Because I demonstrated that female elephant seals produce different variants of attraction calls, I reevaluated their stereotypy while controlling for the attraction call variant. I found that female elephant seals have a higher level of stereotypy when controlling for call variant, with a linear discriminant analysis correctly assigning 50% of the calls to the correct female when controlling for call variant, and correctly assigning 37.5% of the calls when not controlling for call variant.
In summary, my results suggest that mother-pup recognition is mutual in northern elephant seals, but indicate that northern elephant seal mothers are primarily responsible for maintaining contact with their pup during dependency, as the pups do not consistently respond to their mothers’ vocalizations until the last week of the nursing period. Adult females produce calls with enough vocal stereotypy to allow for individual recognition, and they make distinct variants of attraction calls, indicating they have a larger vocal repertoire than previously assumed. Future research should further investigate adult female northern elephant seal vocalizations and how they potentially differ across ontogeny and among behavioral contexts.
| Identifer | oai:union.ndltd.org:CALPOLY/oai:digitalcommons.calpoly.edu:theses-4560 |
| Date | 01 July 2024 |
| Creators | Murphy, Molly |
| Publisher | DigitalCommons@CalPoly |
| Source Sets | California Polytechnic State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Master's Theses |
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