Lyrebirds trick mates into staying in bed
Superb lyrebird are large songbirds only found in forests in Australia. They’re famous for their incredible ability to mimic sounds - from forest creatures to drills - and they also put on elaborate song and dance displays for potential female mates. Now, scientists have uncovered another sexual song the male lyrebird will sing, which is the one you just heard. It is, they think, an imitation of what’s called a ‘mixed species mobbing flock’ - essentially the alarm calls small birds will make if they see a predator. And it looks like the male birds make these sounds to deter females from running off when they’re trying to mate with them. Eva Higginbotham heard from the University of Wollongong’s Anastasia Dalziell how she made the discovery...
Anastasia - I was recording a very nice male, and the male had just paused in his dawn singing. He'd just taken a break. He was eating some worms. He was quiet and sort of scratching, digging for more food along the ground. And suddenly I saw him stand up straight, and throw his tail over his head, and a female walked into the scene. It was a very exciting moment. And then the odd thing was, he then ran off away from the female, but straight to one of his many display mounds. So these are the circular patches on the forest floor, and she followed him and then I had to follow them. It was really difficult because the forest floor was littered with fallen-over gigantic trees, and hidden things to stumble over. And it was well above my knee in bracken, and it was quite a difficult run. It was really a very intense moment for everyone involved, but I got there and I got to the mound where he was performing his song and dance, to play to the female. She was on the mound with him. It was amazing to see. And then just at the moment that he got on top of her, he switched to this mobbing flock mimicry. It was really clear to see it happen. It was very abrupt. And then of course he was on top of her for about, it was 45 seconds or so, and throughout he was mimicking the mixed species mobbing flock.
Eva - Essentially the male birds, while they're mating, they start doing this amazing mimicry, trying to sound like lots of other upset, small birds that have noticed a predator nearby?
Anastasia - Exactly. So of all the wonderful sounds that the male superb lyrebird can imitate, and does at other times, it's this moment, which you can think, perhaps it's the peak of sexual selection. He's mimicking the buzzy alarm calls. It's absolutely extraordinary.
Eva - Why do you think they're doing this?
Anastasia - This is extremely difficult to interpret, but it wasn't until a bit later when we started to put cameras on male display mounds, so these sort of camera traps, to really film the males during their displays and during their sexual interactions with females, that we started to get a handle on what we think is going on, and noticed that there was another context in which males were switching to the mobbing flock mimicry. And this happens when a female approaches the male on his display mound. And as we'd seen in the other examples, he puts on a big song and dance display to her with his tail over his head and the full lyrebird specific songs. But often these dances don't end in a mating. They end, rather, when the female steps off the mound and seems to go away. And it was the moment the female stepped off, that a male would stop singing his song and dance display, and switch to this mobbing flock mimicry. So now we had two sexual contexts in which the male was producing the mobbing flock mimicry, during copulation itself, and when the female was attempting to leave the male without mating. It was a very strong relationship between female behaviour attempting to leave, and male production of mobbing flock mimicry. So we thought about this and we concluded the best explanation that explains his use of it in both contexts, is that he's attempting to prevent the female from ending the sexual interaction before he's managed to transfer sperm to her, saying something like baby, it's dangerous outside, stay here, safe with me.
Eva - How similar is this mimic of the mobbing flock sound to the real mobbing flock sound? And is it similar enough that the lyrebird females definitely think that this is a real mobbing flock?
Anastasia - We tested the similarity in two different ways. And the first way we did it is we compared the acoustic properties, measured acoustic properties of male mobbing flock mimicry, and then recordings that we've made of actual other species in a mixed species, mobbing flock. And we compare the acoustic parameters and we concluded that they were indeed remarkably similar. And then the second way we tested is by conducting an experiment to test whether birds perceive the similarity between the mimic and the model like we do. So I did a playback experiment by placing a speaker in a forest, and broadcasting the sound of lyrebird mimicry of the mobbing flock, or recordings of real mixed species mobbing flocks. And then we scored how these other members of the forest, other birds responded to those. And we found that as far as their behaviour was concerned, they behaved in the same way, regardless of whether it was a mimicry, or the real mixed species mobbing flock. So it's quite convincing evidence that birds with their very different hearing from ours, also perceive the similarity between the lyrebird mimicry and a real mobbing flock.