Hearing in Birds: What Changes From Air to Water

Abstract

There are ∼10,000 species of birds in the world. Of these, there are ∼820 diverse species that live on or near water, many of whom dive when foraging for food. At one end of the diving continuum, diving ducks of the family Anatidae, which contains 158 species of ducks, geese, and swans, can dive to depths of tens of meters for seconds up to a minute or two. At the other end of the continuum is the family Spheniscidae, which includes 17 species of penguins. The most extreme diver among all birds, the Emperor penguin, can dive to depths of 500 m and remain submerged for over 20 min (Meir et al. 2008). As our oceans and waterways become increasingly noisy, it is important to consider the potential impact of this noise on these birds. Although vision is surely important to birds, many of these diving bird species dive to depths where there is little light available, often dive at night, and forage cooperatively (Croxall et al. 1988; Hunt et al. 1993; Kooyman et al. 1992; Speckman et al. 2003). These behaviors probably depend on a sense other than vision. The use of sound for communication, navigation, and foraging in many marine mammals and fish makes hearing a prime candidate. Indeed, hearing is quite important for many diving bird species in the air. Both Emperor and King penguins identify their partners through individually distinctive vocalizations among several thousands of unrelated birds in the tightly packed, noisy colony (Aubin et al. 2000; Jouventin 1982). However, whether diving birds use their hearing in support of similar behaviors underwater is unclear.