Older killer whales make for more successful mommies

Washington, Feb 3 (ANI): Older killer whales (Orcinus orca) nearing menopause are more successful in rearing their young, according to a study.

The research has shown that estimated survival rates for calves born to these older mothers were 10 percent higher than those for other calves.

For the research, Eric Ward from the Northwest Fisheries Science Center, Seattle, USA, and colleagues studied killer whales inhabiting the inland and nearshore waters of Washington state (USA) and British Columbia (Canada).

They used a 30-year dataset collected by the Center for Whale Research and Canada's Department of Fisheries and Oceans.

"During annual photographic surveys, nearly every individual in the population has been recorded. Each animal has unique pigmentation, scars, and fin shapes, allowing us to track the survival and reproductive performance of each female over time," he said.

The study was aimed to investigate what benefits killer whales derive from the menopause.

One theory, termed the "attentive mother hypothesis", is that giving birth to calves and then losing the ability to reproduce helps the mother to focus on bringing up her offspring, without wasting time and energy on further pregnancies.

The findings support the theory to an extent in that during a calf's first year of life, having a mother who was nearing menopause increased chances of survival.

Ward said: "We found that the oldest mothers may also be the best mothers. Older females may be more successful in raising young because of maternal experience, or they may allocate more effort to their offspring relative to younger females".

The study is published in BioMed Central's open access journal Frontiers in Zoology. (ANI)