Magpie sings with Butcherbird

Australian Magpies are not corvids like European or American Magpies. They are actually related to the Australian Butcherbird. They often share territories and we have observed them joining the Magpies attacking a snake. We often hear them communicate with another Butcherbird in the distance and sing at the same time as the Magpies. It could be a coincidence or it might be that it is somehow triggered by the voice of the Magpies. We have no way of knowing what really goes on in their minds, but it is rare to see both of them singing in such close proximity to each other.