Rolan wrote,
Another possibility is that the "victim" heron was ill. When a Mute Swan was purchased to complete the pair at Madigan Army Hospital about two years ago, the resident bird was extremely aggressive toward it. When the new bird later died, a necropsy revealed that the cause of death was some severe intestinal problem, I believe.

So are you suggesting that birds have some kind of mercy-killing ethic among themselves, or that they kill sick cohorts to prevent spread of whatever disease they have, or what? That may sound sarcastic, but I'm not really trying to be funny or cute. The reported behavior was so weird, in my estimation, so exceptional, that it requires a serious explanation, and one that's biologically plausible.

Burt Guttman
The Evergreen State College
Olympia, WA 98505 guttmanb at evergreen.edu
Home: 7334 Holmes Island Road S. E., Olympia, 98503