The Purple-backed Thornbill boasts the smallest bill of any hummingbird. Males are a brilliant purple above with forked purplish-black tails. Females are green above and white below with green spots. These tiny hummingbirds live around the borders of humid forests, in the semi-open highlands, and in páramo. During the wet season, birds migrate to higher elevations. When feeding, Purple-backed Thornbills search for insects by gleaning and hawking, or hover at flowers. They often gather with other hummingbirds in flowering trees where they frequently perch in the treetops. During courtship displays, males dance in arc patterns back and forth in front of females and sometimes make a loud cracking sound while doing so.