Day 11: Older killer whales make best moms

Killer whale with male calf, from Eurekalert.org

I silenced my Inner Rational Scientist here, and went for the cute factor. How could I resist?

There actually is some science. It appears killer whale calves born to older mothers may be in better … um, flippers.

Eric Ward, a conservation biologist at the Northwest Fisheries Science Center in Seattle, is lead author on a new study reporting that calf survival rates were 10 percent higher among killer whale moms nearing menopause. The study appears in the journal Frontiers in Zoology.

The research team studied killer whales inhabiting the inland and near shore waters of Washington state and British Columbia, in Canada, including 30 years of data from 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,” Ward said in a press release. “Each animal has unique pigmentation, scars, and fin shapes, allowing us to track the survival and reproductive performance of each female over time.”

The authors propose that giving birth to calves and then losing the ability to reproduce might help the mother to focus on bringing up her offspring, without wasting time and energy on further pregnancies.

“Older females may be more successful in raising young because of maternal experience,” Ward added, “or they may allocate more effort to their offspring relative to younger females.”

Killer whales are extremely long lived, with one female believed to be more than 90 years old. Males rarely live past 50. Females can produce their first calf as early as age 10, and continue to reproduce until their early 40s.