Main food taken
Adults eat both fruit and arthropods, but nestlings are raised almost entirely on arthropods (Riehl and Adelson 2008). Arthropods taken include dragonflies, mantids, grasshoppers, caterpillars, walking-sticks, spiders, and smaller insects including flies, beetles, and hymenopterans (Skutch 1948, Riehl and Adelson 2008). Fruits taken include drupes, berries, fruiting spikes, and arillate seeds, including Castilla, Cecropia, Trichilia, Spondias, Byrsonima, Sciadodendron, Ficus, Ocotea, Piper, and Muntingia (Skutch 1948, Leck 1969, Scott and Martin 1984, Stiles and Skutch 1989, Riehl and Adelson 2008).
Few quantitative data exist on the relative proportions of fruit and insects in the diet, and it is likely that these proportions change seasonally in deciduous forest habitats that experience seasonal fluctuations in arthropod abundance. Dickey and van Rossem (1938) investigated stomach contents of 10 adult Black-headed Trogon specimens from El Salvador and found that six contained fruit, three contained caterpillars, and one contained both fruit and a caterpillar. In deciduous forest in Santa Rosa National Park, Costa Rica, Riehl and Adelson (2008) found that adults feed primarily on arthropods during the rainy season. Fruit accounted for 10.5% of items and 6.1% of biomass consumed by adults, with lepidopteran larvae (mainly moth caterpillars) accounting for 78.6% of items and 83.1% of biomass. Nestlings were also fed mainly on lepidopteran larvae (74.5% of items and 80.8% of biomass) as well as orthopterans, mantids, and phasmatids. Fruit accounted for just 2.2% of items and 0.6% of biomass in the nestling diet. The nesting season coincides with peak caterpillar abundance (Janzen 1988, Riehl and Adelson 2008), suggesting that Black-headed Trogons time their reproduction to coincide with insect rather than fruit availability. Quantitative diet information is not available for other times of year; diet may include a higher proportion of fruits and flowers when caterpillar abundance declines.
Microhabitat for foraging
Forages at many levels of forest from midstory to canopy. Like other trogons, does not forage on ground. In deciduous forest, often searches for insects high in open canopy of large legumes (Pithecellobium, Enterolobium; C. Riehl personal observations). Also forages in outer layers of canopy in large fruiting trees (Sciadodendron) or swoops down to pluck fruits from shrubs in the forest interior (Ocotea, Piper). Often seen foraging at forest edges (along roads), in large isolated trees in pastures and rural areas, and in forest gaps (C. Riehl personal observations).
Food capture and consumption
Foraging individuals typically sit on an exposed perch or in open canopy, peering about and remaining in the same place for several seconds or minutes at a time. Fruit or insects are usually plucked from vegetation during short, fluttering sallies. Most food is taken on the wing, while briefly hovering, and consumed back on the perch (Leck 1969, Stiles and Skutch 1989, Johnsgard 2000). Skutch (1948) wrote that "[b]etween their swift darts to seize food, the Citreoline [i.e. Black-headed] Trogons rest motionless for protracted periods, perching very upright with their long tails directed almost vertically downward". Fruit is often swallowed immediately; caterpillars and other insects are banged vigorously against the perch to extract the guts. Hairy caterpillars are consumed infrequently; when captured they are rubbed against the perch to remove the hairs (C. Riehl personal observations). Occasionally forage in loose groups of 3 – 12 individuals.
Arthropods: Adults preferentially consume small insect prey and feed larger insects to nestlings. Nestlings consume a higher proportion of mantids and phasmatids than adults do, and caterpillars fed to nestlings average 70% larger than those consumed by adults (Riehl and Adelson 2008). The majority of caterpillars brought to nests were very large (≥6 cm) and walking-sticks (Calynda) brought to the nest were as large as 12 cm and had to be inserted sideways through the nest cavity entrance. Joyce and Janzen (unpublished data) found that adult trogons are highly selective in the caterpillars that they feed to nestlings. Trogons feed a disproportionately high number of late-instar larvae to nestlings (regardless of absolute mass of the larvae), suggesting that adults select prey that contains the largest reserves of fat and protein relative to indigestible material. In addition, Black-headed Trogons appear to prefer to deliver saturniid larvae to nestlings.
Fruit: Limited data from the Santa Rosa National Park suggest that Black-headed Trogons fed on Byrsonima crassifolia, Ficus spp., and Sciadodendron excelsum more frequently than the abundance of those species would predict (indicating preference) and Cecropia and Piper less frequently (indicating avoidance; Riehl and Adelson 2008). However, these results were drawn from small sample sizes. Often returns to the same fruiting trees for several days in a row (Leck 1969, C. Riehl personal observations).
Nutrition and energetics
No information available.
Metabolism and temperature regulation
Adults pant and droop wings when hot, particularly at exposed nesting sites. Skutch (1948) noted that adults frequently incubated for many hours at a stretch in the enclosed, black termitaria, which presumably reach high temperatures when exposed to direct sun. Bennett and Harvey (1987; cited in Johnsgard ) found that the congeneric Black-throated Trogon (Trogon rufus) had a low resting metabolic rate compared to other birds of the same body size, a pattern which is possibly characteristic of the other trogons as well.
Drinking, pellet-casting, and defecation
Adults do not remove fecal matter of young from nesting cavities, accumulating in a layer at the bottom of the nest in which “maggots swarmed” (Skutch 1948). Adults regurgitate large seeds from fruits that have been swallowed; Skutch (1948) recorded that about a dozen seeds “the size of cherry stones” accumulated in one nest cavity.