Vocal recognition between mothers and pups in the northern elephant seal (Mirounga angustirostris) and northern fur seal (Callorhinus ursinus)
Date
1989
Authors
Insley, Stephen James
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Abstract
I have described vocal recognition between mothers and their offspring in two species of pinnipeds that differ fundamentally in their breeding behaviour: Northern Elephant Seal (Mirounga angustirostris) females and offspring are normally together throughout the nursing period; Northern Fur Seal (Callorhinus ursinus) females regularly separate from their offspring while nursing. The objectives were (1) to describe recognition behaviour generally, (2) to describe recognition vocalizations in particular, and (3) to compare the structural variation of recognition vocalizations in the two species. There were two predictions: (1) recognition vocalizations should be individually distinct in females and pups of both species, and (2) because individuality should be more pronounced in a species where female-pup separations are common, the Northern Fur Seal female-pup recognition vocalizations should be more individually stereotyped than those of the Northern Elephant Seal. Tape recordings and behavioural observations were made at Ano Nuevo Island, California, and St. Paul Island, Alaska, during the 1988 breeding seasons. A sample of 20 calls per seal from each of 12 Northern Elephant Seal and 8 Northern Fur Seal female-pup pairs was analyzed using 15 acoustic variables. Baseline information is provided for females and pups of both species through descriptive and quantitative accounts of both mother-pup recognition behaviour and recognition vocalizations. Analyses of variance showed the calls of individual seals to be acoustically distinct in all cases. Measurements of within- and between-individual variation ( coefficients of variation, added variance components, and stepwise discriminant analyses) revealed that Northern Fur Seal recognition vocalizations are more stereotyped than those of the Northern Elephant Seal, as predicted. Principal components and cluster analyses were used to compare the structure of calls between females and pups and across species. The results indicate that selective pressure to develop vocal recognition exists in both species but is greater in the Northern Fur Seal.