Coulicou à bec jaune vs Coucou gris

The most reliable field mark to differentiate the Yellow-billed Cuckoo from the Common Cuckoo is the bill color: Yellow-billed Cuckoo has a distinctive yellow lower mandible, while the Common Cuckoo has a dark bill. Both species have similar body shapes, but their vocalizations and habitats can also help in identification.

Check the bill color first: Yellow-billed Cuckoo has a yellow lower mandible, while Common Cuckoo has a dark bill. Use vocalizations and habitat preferences as secondary clues if needed.

The Yellow-billed Cuckoo has a yellow lower mandible, whereas the Common Cuckoo has a uniformly dark bill. Both species have similar overall plumage tones, making bill color a key distinguishing feature.