No matter how stealthy, a bat can't hide its approach from sharp-eared moth victims. As soon as a target hears an inbound attacker, it takes immediate evasive action. But that isn't the moth's only line of defence. Jesse Barber from Wake Forest University explains that some moths taste bad to deter predators. Some of these species also emit ultrasonic clicks to warn attackers off. While bats quickly learn to avoid the warning clicks of unpleasantly flavoured moths, it wasn't clear whether the predators would extrapolate and avoid all clicking moths, regardless of whether they tasted good or bad. Curious to find out more about bats' responses to warning clicks, Barber and his supervisor, William Conner, set about filming naïve bats' reactions to clicking prey with 3D high speed video to find out how they responded to clicking mimics and whether they could discriminate between the clicks of good and bad tasting species ().
According to Barber there are two ways in which moths mimic bad tasting moths for protection. Some tasty moths disguise themselves to look as if they taste bad by making ultrasonic warning clicks; they are known as Batesian mimics. However, bad tasting species also mimic the warning clicks of other unpleasantly flavoured moths in the hope that they will be attacked less frequently; these are known as Müllerian mimics. But before Barber could begin analysing naïve bats' responses to bad tasting tiger moths and their mimics, he had to find baby bats that had not learned to recognise tiger moths' warning clicks.
Having contacted surrogate bat-mum Barbara Schmidt-French at Bat Conservation International in Austin, Texas, Barber learned to rear tiny red bat and big brown bat pups and trained them to catch moths in a confined space in the lab. Barber then switched to offering the animals two species of foul tasting clicking tiger moths as he filmed the bats' super fast reactions. After five nights, Barber switched the moths, replacing the original tiger moth species either with a pleasant tasting Batesian mimic or a vile flavoured Müllerian mimic and filmed the young bats' reactions to the new species'click patterns.
Working with Nick Garrett to digitise the 3D highspeed movies of the bats'antics and Brad Chadwell to analyse the bats' manoeuvres, Barber found that the young bats soon learned not to approach bad tasting moths when they heard the insect's warning clicks. And after five nights of encounters with the unpleasant tiger moths the young bats were steering well clear. However, when Barber introduced the clicking mimics, the bats' behaviours changed. Most of the bats began moving closer than they had done the night before, but still called the attack off at the last moment. The bats were still interpreting the clicks as warnings to stay away, but they had realised that there was a new species in the enclosure and decided to take a closer look. And some of the bats that were presented with a pleasant tasting mimic eventually saw through the subterfuge. After 5 nights they began ignoring the warning clicks and started feasting on the tasty mimics. Barber explains that he could only get this highly detailed information about the bat's manoeuvres with the video system. `This could only have been done with 3D high speed video,' says Barber.
So the bats take heed of the warning clicks that different tiger moth species emit, giving all tiger moths a wide berth once they are wise to the warning. But their hearing is subtle enough to pick up minor differences between species' clicks, allowing them to take a closer look at unfamiliar moths before being absolutely sure that they want to avoid the bad taste that some moth mimics may leave behind.
