The Green-crowned Brilliant's feeding behavior is characterized by fast, darting flight, and a tendency to perch while feeding, usually clinging to inflorescences with its feet (e.g. Stiles and Skutch 1989). Despite its size, it is usually rather inconspicuous (Ridgely and Gwynne 1989), and may alight on inflorescences without a sound (J. Taylor pers. obs.).
Male Green-crowned Brilliants are known to intermittently defend large Marcgravia plants in Costa Rica (Stiles and Skutch, 1989); however, the species also appears to trapline (use a feeding circuit), at least at some times of year, although interference competition still occurs infrequently with other species (J. Taylor pers. obs.), and probably with conspecific individuals.
Male hummingbirds are typically polygynous (Schuchmann 1999), and the behavioral observations documented by Sánchez et al. (2000) certainly suggest that male Green-crowned Brilliants do not assist females during the nesting phase of the breeding season.
Social and interspecific behavior
Brief hostile interactions with other hummingbird species have been noted to occur infrequently at Heliconia flowers in Costa Rica (Taylor 2005); however, the frequency and nature of interspecific interactions is expected to vary with location and season.
There do not appear to be any observations documented on the predation of this species, although hummingbirds in general may be taken opportunistically by forest raptors.