Flies rapidly for short distances with undulating movement. When leaving nest, may suddenly drop downwards before rising again (C. Riehl personal observations). Does not forage on ground, but may perch on ground when leaving or arriving at a nest site situated near the ground (Skutch 1948). Maneuverable in flight; capable of foraging on the wing, mid-air turns, and short bouts of hovering.
Preens frequently while perched. Incubating adults of both sexes often have the entire distal quarter of the tail bent sideways from being confined in the nesting chamber (C. Riehl, unpublished data). Adults that have been brooding or feeding nestlings may have stained and soiled belly feathers (Skutch 1948).
The extent of territoriality in this species is not known. Both males and females are vocal at the nest site, but it is not known whether these vocalizations primarily function in territory advertisement, pair bonding, or both. Males at the nest site call repeatedly, often simultaneously with males at neighboring sites (Riehl 2008). After the pair bond has formed, nesting pairs also call in tandem (duet). Both breeding and non-breeding individuals gather in loose assemblages of 3-12 individuals that travel together through the forest, calling and flying at one another (see Social and Interspecific Behavior). Nesting pairs tolerate these traveling groups in the vicinity of the nest, and will even join the assemblages as they pass through the area (Riehl 2008). However, foraging individuals appear to avoid occupied nest sites and males at neighboring nest sites may meet between nests to call together, indicating the existence of territorial boundaries (C. Riehl personal observations).
Little known. Pairs of Black-headed Trogons are socially monogamous; occurrence/frequency of extra-pair copulations is not known. Pairs are stable during the breeding season; it is not known if the pair bond persists across years. Copulation has not been observed. Courtship behavior has not been described; assemblages of calling males form during the breeding season but this behavior does not seem to be related to mate choice (see Social and Interspecific Behavior).
Social and interspecific behavior
Adult Black-headed Trogons of both sexes gather in groups of 3 – 12 individuals that travel through the forest, calling and flying at one another (Riehl 2008). Males call more frequently than females in these assemblages and often outnumber females, leading to the suggestion that communal calling plays a role in mate choice (Skutch 1972, Howell and Webb 1995). Several other trogon species have also been observed collecting in similar groups, which have been termed "quasi-leks" (Brosset 1983: 8), "noisy leks" (Howell and Webb 1995: 432), and "lek-like assemblages" (Johnsgard 2000: 113).
Some characteristics of Black-headed Trogon groups support this hypothesis: assemblages contain more males than females, and males chase other individuals (of both sexes) from perch to perch significantly more often than females do. Other evidence, however, suggests that calling assemblages are unrelated to courtship (Johnsgard 2000, Riehl 2008). Assemblages form throughout the breeding season, even after pairs have formed and nesting is well underway. Furthermore, both breeding and non-breeding individuals participate in these groups; nesting birds will leave nests for short periods of time to join calling assemblages that are traveling through their territories. Groups typically travel through multiple territories and investigate active nest sites as well as unoccupied termitaria, suggesting that these activities may be related to prospecting and evaluation of potential future nest sites. Individuals in groups frequently consume fruit and insects while calling and chasing one another, but prey capture rates of trogons in groups are not higher than those of trogons foraging alone (Riehl 2008).
Nests are built in occupied nests of Nasutitermes termites, which wall off the portions of the termitarium excavated by trogons (see Reproduction). In Santa Rosa National Park, Costa Rica, observed to occasionally forage in groups of up to 12 individuals that may also contain 1–2 Elegant Trogons (Trogon elegans; C. Riehl personal observations). At the same location, nesting Black-headed Trogons most frequently alarm-called at Orange-chinned Parakeets (Brotogeris jugularis). These also nest in termitaria and appear to compete with trogons for nest sites. Though they nest earlier in the season than Black-headed Trogons, pairs of Orange-chinned Parakeets remain mated year-round and apparently continue to defend nest cavities after their chicks have fledged. Three of 14 trogon nests sites had been used by pairs of Orange-chinned Parakeets earlier in the year, which occasionally returned to the cavity to harass the trogons currently nesting there. On five occasions, pairs of parakeets perched on or near trogon nests and called loudly until trogons drove them off. At one nest, a pair of parakeets repeatedly harassed the adult trogons and the nest was eventually abandoned (Santa Rosa National Park, 2005; C. Riehl unpublished data).
Nesting Black-headed Trogons were also observed to give alarm calls at white-faced capuchins (Cebus capuchinus), golden-mantled howler monkeys (Alouatta palliata), black iguanas (Ctenosaura similis), tiger rat snakes (Spilotes pullatus), White-throated Magpie-Jays (Calocitta formosa), and Roadside Hawks (Rupornis magnirostris; Riehl 2005).
Kinds of predation
Predation on adults is not well documented. Vehrencamp et al. (1977) found remains of Black-headed Trogons on three occasions at a communal roost of Vampyrum spectrum, a 180-g carnivorous bat, in riparian forest in Costa Rica. All three instances of predation were during the dry season, indicating that the individuals taken were adults.
As in most tropical birds, predation is more frequent on eggs and nestlings than on adults. Skutch (1948) found one nestling dead in a nest that had been decapitated by a carnivorous mammal (possibly a weasel) and consumed by ants. Of 15 nests in Santa Rosa National Park, Costa Rica, 10 were successful (66%); this is likely an overestimate, since not all nests were found at the beginning of the nesting cycle (C. Riehl unpublished data). One of the 5 nest failures was due to predation by a large adult tiger rat snake (Spilotes pullatus) that consumed the nestlings.
Response to predation
Adults do not defend nests vigorously. During incubation, adults disturbed at the nest leave quickly without defending the eggs. After nestlings hatch, adults either leave the nest or perch nearby, giving the low "cuck" alarm call. Nesting conspecifics in neighboring territories will occasionally gather in response to alarm calls at a nest (C. Riehl unpublished data). Nesting adults sometimes fly at predators near the nest, particularly monkeys (Riehl 2005).