Budgerigars (Melopsittacus undulatus), also known as parakeets, are popular cage birds the world over. These small Australian parrots have proven to be excellent subjects for studying how birds hear. In fact, more is known about hearing and auditory discrimination in this species than in any other bird. The audiogram, or absolute threshold curve (Okanoya & Dooling, 1987), shows the softest tone an animal can hear at different test frequencies. The audiogram for the budgerigar, measured behaviorally, is shown to the left in comparison to the human audiogram. Typical of most small birds, budgerigars hear best between 2-5 kHz and less well at lower and higher frequencies. Compared to most birds, humans hear better at low frequencies and much better at high frequencies. As can be seen in this figure, a 10 kHz pure tone must be at level of about 20 dB SPL to be heard by humans and almost 100 dB SPL to be heard by budgerigars. The calls and songs of most birds including budgerigars, though they sound high-pitched to the human ear, actually have most of their energy concentrated in the region of 2-5 kHz (see: What budgerigars say). Thus, for most species of birds, the frequencies contained in their songs and calls are the same frequencies to which the ear is most sensitive.

Besides the simple detection of soft sounds, there are many other tests to measure hearing function including the ability to discriminate intensity, frequency, or time differences between simple sounds such as tones and the ability to discriminate among more complex sounds such as bird vocalizations, harmonic complexes, or human speech sounds. Budgerigars do very well on such tests and have even been shown to hear many consonant and vowel speech sounds as humans do. This explains, in part, why budgerigars are such good speech mimics.