Rufous-tailed Jacamars are strictly insectivorous and eat flying insects such as butterflies, dragonflies, and wasps. Prey items are in the following orders: Hymenoptera, Lepidoptera, Orthoptera, Hemiptera, Odonata, and Diptera (Pinheiro et al 2003). Individuals in central Brazil (subspecies rufoviridis) were found to prefer 1) small insects, probably Diptera and Hymenoptera; 2) larger Hymenoptera; and 3) Lepidoptera, with more butterflies than moths. No differences in prey preferences were found between the sexes (Pinheiro et al 2003).
The species has been studied in depth in terms of predation on butterflies, including Batesian and Mullerian mimics. Chai (1986) found the following in regards to butterfly consumption:
1) The butterfly needs to be moving to be considered prey.
2) Butterflies in an array of sizes can be captured/handled.
3) Jacamars largely sight-reject inedible butterflies and quickly snatch edible ones.
When prey were taste-reject, the process was brief and most butterflies survived. In terms of determining acceptability, Chai (1986) believes that the birds are able to detect morphological and behavioral characteristic: "Local butterflies unacceptable to jacamars are generally conspicuously colored and mimetic, have long slender bodies, and fly slowly and regularly. Acceptable butterflies are generally cryptic (on at least one side), with short, stout bodies, and fly fast and erratically." Additionally, Chai (1998) demonstrated the importance of color as a cue in a feeding experiment by painting butterflies with colors corresponding to unacceptable or acceptable prey. Langham (2004) showed that this species could even detect fine-scale differences between morphs of the Heliconius butterfly, avoiding familiar morphs and selecting against novel morphs over time.
Another study by Chai (1996) resulted in the following information about butterfly consumption by young jacamars:
1) Naive young jacamars did not show any inhibition to attacking butterflies but quickly taste-rejected unacceptable ones.
2) With some experience, young jacamars displayed reluctance to attack certain classes of butterflies.
3) Specific species were either consumed or rejected a majority of the time, demonstrating consistency.
4) Young jacamars rapidly learned associations between visual characteristics and palatability.