one difference I observed

送交者: jxh 于 2009-06-19, 13:55:31:

回答: Grey Heron, Blue Heron, whos is who? 由 cornbug 于 2009-06-19, 13:45:08:

For grey heron, the black strip on its head goes through its eyes. For blue heron, there is some gap between its eyes and the black strip.

That might be. Here is another one from Japan - cornbug (157 bytes) 2009-06-19, 14:16:02 (335687)
- 这老兄比较倭 (无内容) - ziren (0 bytes) 2009-06-19, 19:13:13 (335758)