I’ve studied cuckoos for years and I’m still at it. Often call the males in which come at first but after a few times don’t bother. I think they must be immature birds. Watched two on Sunday actually mating so I’ve a female laying in my patch. Last year lucky enough to watch one laying in a meadow pipits nest, which was a fantastic thing to watch. She was down on the heather for 2 hours, sat still, weighing everything up. Then she fluttered a few yards, dived into the grass, searched, found and layed. I could sit for hours watching them