Single SB-600 flash with green gel manually fired from behind each of four trees during an ir-remote-triggered bulb exposure.
Fun story: Ellen just reminded me that while we were walking down the dark road to take this photo, two staff members from the YMCA camp drove by in a golf cart and stopped at another tree only a few feet away. One said to the other, while gesturing upward with his flashlight, "So this is the tree that I saw the bear cubs climb up into last night."
UPDATE: Thanks for all the extra attention from the Strobist blog, David! I'm simultaneously shocked, honored, proud and thrilled. I only recently got on the Strobist kick when my friend, Kim and his wife invited me, my wife and another friend over to start watching your DVD set about a month ago. During the sessions, we watch a few chapters and then practice our newly learned techniques. What we have lovingly dubbed StrobeFest2008 continues this weekend with Part III. I'm really grateful to you and the Strobist community for sharing your knowledge, wonderful ideas and encouragement!
Could it possibly be even better On Black?