The lep community has known for quite some time that moths are capable of detecting and taking evasive action when they hear the vocalizations of predators, especially bats. And while scientists have found auditory sensing organs on some butterflies as well, if and how they use these has not been as extensively studied.
Researchers from the University of Arkansas and their colleagues, however, have discovered that males of the Postman butterfly, Heliconius melpomene, detect and take evasive action when the calls of one of their resident bird predators are played.
Rufous-tailed jacamars are widespread and common insectivorous birds in the range of Heliconius melpomene plessini, the subspecies the researchers studied. The birds look like a forest version of a kingfisher, with long pointed bills that they use to capture insect prey, especially wasps. But butterflies and dragonflies are also on the jacamar menu in the Central and South American habitats where the Postman flies.
Heliconius butterflies generally have evolved a wide rage of defense mechanisms against predation, the research team noted. They are toxic, unpalatable, display aposematic colouration, form Müllerian mimicry rings, and roost communally to avoid bird and bat predation. This might suggest that they don’t really need much extra predation defense from jacamars.
Nevertheless, when the scientists played jacamar calls in the greenhouse where the Postman butterflies were raised, the males immediately changed behavior, increasing their fluttering and walking instead of flying during the jacamar playback and for a short period (about 3 minutes) afterwards. There was no longer-term behavior change, nor did females show any reaction to the jacamar calls.
Nor did they react to background noise played in the greenhouse, or to the calls of two other migratory predators in their range — eastern and tropical kingbirds. And even the calls of the jacamar failed to change the butterflies’ intersexual behavior.
“Heliconius melpomene plessini butterflies changed their behaviour in response to predatory rufous-tailed jacamar calls but did not change their behaviour in response to predatory Eastern kingbird or tropical kingbird calls,” the team concluded. “We found a sex-specific difference in behaviour, where males, but not females, increased their fluttering and walking behaviours during the playback of the rufous-tailed jacamar calls. The observed behavioural changes in response to rufous-tailed jacamar calls are short-term and do not persist over an extended duration of time.”
The researcher posit two possible reasons for why the butterflies reacted to jacamars but not kingbirds. One, the jacamars are a year-round threat, while the kingbirds are migrants that also eat a lot of fruit during their winter sojourn in the tropics where the Postman is found. Overall, the scientists suspect, predation pressure from the kingbirds could be much less than from jacamars.
Two, the calls of the two kingbirds are in a much different auditory frequency than the jacamars, and it’s possible the auditory organs of the butterflies can “hear” the jacamar but not the kingbirds.
That the butterflies are only reacting to predatory bird calls was studied by playing recordings of toco toucan calls in the greenhouse. The toucan calls are in the same frequency range as jacamars, but toucans don’t eat the butterflies. The butterflies had no reaction to the toco toucans.
The authors suggest this might be similar to the scenario where “aposematic striped skunks (Mephitis mephitis) perform anti-predatory behaviour in response to the calls of the great horned owl (Bubo virginianus) from which they are not chemically defended, but not in response to the calls of the coyote (Canis latrans), from which they are chemically defended.”
As to the sex-specific behavior change, the authors note that the males of a number of other species across the animal kingdom react differently than do females. “This male-specific response to predators is similar to that found in other species, and may reflect sexual dimorphic predation pressures,” they surmise, since males range widely through the middle of the forest landscape while females are mostly in the understory near their larval/food host plants. Since jacamars are “hawking” feeders — they dart out from perches to snag passing insects — they might pose more of a risk to male Heliconius butterflies than to females.
The paper is currently available as a preprint that has not yet been reviewed on bioRxiv.
Alternatively, you can read a PDF version in the LepLog library:
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