Are penguins able to hear although they seem to have no ears? Yes, penguins are able to hear but they have no pinnae. All other structures do exist that are relevant for hearing.
The ear of a penguin begins with the ear canal which leads to the middle ear. If you look very closely you would recognize an opening near the eye of a penguin which belongs to the ear canal. But you cannot regognize this opening easily because it is covered by special feathers. In birds there is only a single auditory ossicle in the middle ear which is called columella. The sound gets from the middle ear to the cochlea in the inner ear. There the different frequencies of the sound are analyzed. This information is transmitted to the brain. This complete process - from the admission and transmission to the analysis of the sound - is called "hearing".
It was investigated that African Penguins are able to hear sounds with frequencies between 100 and 15000 Hertz. Young human beings can hear sounds with frequencies in a range of 16 to 20000 Hertz.
Hearing is very important in penguins, especially for chicks that want to be fed. So, recognizing the call of their parents is essential. African Penguins are very sensitive for sounds with frequencies between 600 and 4000 Hertz. This range agrees with the frequencies of penguin calls.
Calls with lower frequencies can be transmitted further than calls with higher frequencies. Calls with lower frequencies can even be perceived in a greater distance in a noisy environment. This is an advantage because penguins live in large colonies where it is sometimes very loud.
Jouventin, P., Aubin, T., & Lengagne, T. (1999). Finding a parent in a king penguin colony: the acoustic system of individual recognition. Animal Behaviour, 57(6), 1175-1183.
Saiff, E. (1976). Anatomy of the middle ear region of the avian skull: Sphenisciformes. The Auk, 749-759.
Wever, E. G., Herman, P. N., Simmons, J. A., & Hertzler, D. R. (1969). Hearing in the Blackfooted Penguin, Spheniscus demersus, as represented by the cochlear potentials. Proceedings of the National Academy of Sciences, 63(3), 676-680.