Killer whales are one of only three species able to continue living long after they have stopped reproducing. This allows mothers to spend the rest of their life looking after their offspring.

Scientists are investigating why the animals evolved this trait. Researchers, from Exeter University and York University, have secured funding from the Natural Environment Research Council (NERC) to analyse a dataset of more than 550 killer whales recorded over 30 years.

The dataset, compiled by the Centre for Whale Research in the US, contains birth and death dates as well as details of the genetic and social relationships in two populations of killer whales, which share their menopausal trait with only humans and pilot whales.

"Our main aim is to understand why these killer whales have a menopause strategy that's so similar to humans. Female killer whales stop reproducing in their 30s or 40s but live until they are 90," said Dr Darren Croft of Exeter University, a lead investigator on the study.

The researchers believe the reasons for the menopause in killer whales lie in their unusual social structure.