what I have learned today: resident vs. transient orcas

In the PNW, at least, we have distinct populations of "resident" and "transient" orcas, living in the same area without interbreeding.

http://www.orcanetwork.org/nathist/transients.html

As the first person to systematically observe these whales, Bigg could not have known that the Pacific Northwest is uniquely blessed to provide habitat to two drastically different forms of killer whales, now recognized as living in separate and distinct cultures. In the quarter century since Bigg began orca studies, no migration by either sex from either type into the other has been recorded. Membership in each begins at birth and cultural bonds and identity continue throughout life. Residents and transients differ in diet, vocal traditions, habitat range, morphology (shape of dorsal fin, etc.), pigmentation patterns (such as the eye patch) and genetically. Though they cross paths routinely throughout the inland waters of BC and Washington State, the two forms are becoming, or by some accounts are already, separate species. DNA work indicates that they have not interbred for at minimum one hundred thousand years.