During the first immigration wave, a presser immigrated to my fort. Before the blinking gray "X" went away, they had climbed a tree and fallen to their death.

Note the expedition leader currently stuck up in a tree with a broken foot (from a fall.)

Also, a mason fell out of a tree into the river and drowned.

The cat, and some other dwarves, are injured from pointless excursions into the canopy.