Bioacoustics Theories - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 45

Fig. 3.2 Correlation between frequency and animal mass. At the two extremes are the smallest
birds (e.g., the firecrest, Regulus ignicapillus ) and the largest mammals [e.g., the elephants
( Loxodonta spp.)]. The dashed line represents the regression between frequency at body mass
f M 0.33 M 0.4 (simple linear scaling); the solid line is the predicted relationship f

¼ ¼

(Reproduced with permission from Fletcher 2004 )

influence the acoustic network. The environmental condition of the habitat
constrains the communication efficiency and efficacy between a sender and a
receiver. Environmental conditions affect the quality of the signal and also the
capacity by a receiver to range, that is, to estimate the distance to the emitters.
The environment is an important cause of modification and alteration of the
acoustic signals.
The song when used to communicate over long distances is prone to
modifications by environmental constraints such as topography, vegetation cover,
and natural or anthropogenic noise masking.
The absorption of some frequencies that modify the structure of a signal and its
meaning for a receiver is a common effect.
The acoustic adaptation hypothesis (AAH) is based on the assumption that the
sounds used in long-distance communication are correlated with habitat acoustics.
This hypothesis, first formulated by Morton ( 1975 ) on birds, states that dominant
frequencies and other long-distance calls are the result of an interaction between the
animals and the environment to maximize the transmission efficiency of the emitted
sounds. In this way different habitats interfere differently, according to the sound
frequency bands, and callers try to occupy the frequency bands that have lower
degradation. This consideration holds not only for sounds in air but also sounds in
the waters of the open ocean.
Furthermore, temporal patterns of a sound design can also be affected by environ-
mental constraints. For instance, low-frequency signals travel through the vegetation