Summary:

- The article discusses a deadly H5N1 outbreak that has triggered an unprecedented Caspian tern die-off in Washington state and has also spread to harbor seals.
- The H5N1 virus, also known as avian influenza or bird flu, has been causing significant mortality in wild birds, particularly Caspian terns, in the region.
- The outbreak has raised concerns about the potential for the virus to spread to other wildlife species and the potential impact on ecosystems and human health.