With 73 individuals remaining, southern resident killer whales, or orcas, are the only endangered population of killer whales in the U.S. They spend the spring, summer and fall hunting for salmon throughout the inland and coastal waterways of Washington and British Columbia. Their territory overlaps with northern resident killer whales which hunt for salmon from Glacier Bay, Alaska to the central coast of Washington, and share a similar matrilineal social structure. Both groups face threats such as plummeting salmon stocks, pollution and increased maritime activity. But unlike the population of northern resident orcas, which has been steadily increasing, the southern resident population has declined over the past 20 years.

A team of international scientists has now revealed another possible clue to help explain their struggle for survival. They found that adult males spent more time hunting and catching salmon than females within the southern resident population, with the foraging pattern reversed in the northern population. They also found that southern resident mothers with calves spent less time hunting than northern resident mothers. Joining us now is Jennifer Tennessen, a senior scientist at the University of Washington Center for Ecosystem Sentinels, and the lead author of the study which was published this month in the journal Behavioral Ecology.