a dreadful bird with a pretty tune

Click to enlarge.

This is the European bird who shoots out of the Cuckoo Clock every hour or half-hour or quarter-hour and sings "cuckoo!"

The cuckoo is ... well, rather than be judgmental and moralistic, the technical name for such birds is parasitic. The female lays her single egg in another non-cuckoo's unguarded nest among that bird's eggs. Then the cuckoo flies away and leaves the hatching and feeding and rearing to the non-cuckoo.

The cuckoo egg hatches first, and when the other eggs hatch, the cuckoo hatchling bullies and starves and shoves the other hatchlings out of the nest to their death.