We've always had a successful colony of barn swallows for years. Last year, some magpies started predating their nests so fewer broods succeeded. This year, the swallows returned in April and the magpies were waiting for them. To date we've had no successful broods and many of the birds that returned have left for safer territory. All we hear is the remaining ones being constantly attacked, all day long. Any ideas to deter the magpies would be welcome.
I don't think there is anything you can do, it is nature, magpies will predate, it is in their genes, they are a carrion bird, like crows, jackdaws and many others, and just like other birds, need to feed their young, as well as themselves.
It is harsh, but that is nature, hunt and be hunted, and I know it isn't helpful to the poor swallows who are trying to raise their families also, let along what we see as caring humans.