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Reproductive Behavior and Maternal Investment of Australian Sea Lions


The breeding cycle, breeding behavior, female attendance cycles and pup growth of Australian sea lions were studied at Kangaroo Island, South Australia, during December to May, 1986-87, April to October,1988, and November to March 1989-90. Animals were identified using paint, dye and bleach marks during each breeding season and with tags and natural scars between seasons.

Females exhibited a synchronized, non-seasonal breeding cycle that is unique for pinnipeds. Data from 191 births gave 527 and 532 day intervals between the median pupping dates of the three breeding seasons. Sixteen females had a mean pupping interval of 540 ± 12.0 days (17.7 ± 0.4 months). Comparison to the timing of the breeding seasons during a previous study show a seasonal shift of 3-4 months during a 12 year period.

Breeding females were non-gregarious and parturition sites were spread out in the study area. As a consequence, male territories were plastic in space and time. Tenure on territories ranged from almost continuous occupation to less than one day a week depending on whether females were present. Differential reproductive success of males was low. Males usually attended one female at a time and thus practiced serial polygyny to achieve more than one copulation. Attacks on pups by adult territorial males accounted for 19% of pup mortality during two breeding seasons.

Females suckled their pups for 15-18 months until the birth of the next pup, although 23% did not give birth consecutively each breeding season, and continued to suckle their yearlings for up to 23 months. Female attendance cycles consisted of feeding trips of about two days in length and stays ashore of about 1.5 days, and did nat change over time. Feeding trips were significantly shorter during the winter months of June and July and may reflect a day length affect. Pup age or sex seemed to have no influence on attendance cycles. Male pups were significantly heavier than female pups and grew faster in 1988, but not in 1986-87. Growth rate data of older pups indicate that there was a reduction in the rate of growth at about one year of age but this was not always related to time of weaning.

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