Although they are not external flaps, ducks' ears are somewhat visible. Their feathered ear opening is underneath and at the back of their eyes.
Most lizards have tiny ear openings that are scale-covered, hence not easily noticeable. Some lizards have larger openings for ears.
The external ears of the snakes are not at all visible. They don't hear with the help of some external ears but feel the vibration through the ground and the jawbones.
The feathers over the small, insignificant ears of sparrows are covered. Their ear holes can hardly be distinguished.
Even though they are not external flaps, crows do have visible ears. They have small feather-covered holes in the sides of their skulls.
Ants do not have ears. They sense their environment using other methods, like antennae for detecting vibrations and chemicals.
Fish do not have visible external ears. They have internal ears adapted for detecting vibrations and pressure changes in the water.
Frogs have ears, but their eardrums (tympanic membranes) are located on the sides of their heads, which are often not very noticeable.