Large and striking vireo with stout hooked bill. Olive above and yellow below with distinctive gray-and-yellow head pattern and staring green eye. Sexes similar. Fairly widely distributed in northern South America, where it ranges from lowlands to subtropical forest, up to about 1,800 m. Not easy to see because it stays high in the canopy, where its repetitive whistle is often the harbinger of an incoming mixed-species flock.