 So the wing sound of the crested pigeon warns its allies of danger and we wanted to figure out how it was produced. We noticed it had this unusual eighth primary feather. It's half the width of the neighbouring feathers. So what I wanted to do was really test whether that was the source of the sound. And so to do that we caught some birds, caught some crested pigeons, and then we trimmed that feather and then when we looked at the sound as they took off the sound was completely different. So that's how we could tell that that eighth primary was producing the sound, that high note. Well Darwin spent quite a lot of time talking about these non-vocal sounds, especially in birds. He spent almost as much time talking about the non-vocal sounds as the vocal sounds that birds produce. You know the analysis can be hard sometimes but once you get those results it's really exciting. When we saw those spectrograms, those sound files and could really see that these feathers were causing the sound it was really nice to make a discovery like that to really link our question with its answer. This research will hopefully build into other people doing more comparative studies, exploring these other species' sounds, seeing whether they're signals and seeing whether they're alarm signals. So it's nice to be able to add to Darwin's legacy and hopefully more people will take up the mantle.