Sonic Characteristics of the Landscape - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 32

insects there are no significant relationship between the calling song and T b
(Sanborn and Mat ´ 2000 ). Ambient temperature regulates the sound power of
cicada calling songs. Investigations conducted by Sueur and Sanborn ( 2003 )on
three species of European cicadae of genus Tibicina have found a direct correlation
between ambient temperature and sound power in Tibicina corsica fairmarei ,
T. garricola , and T. tomentosa (Fig. 2.2 ). Similar results have been obtained by
Fonseca and Revez ( 2002 ) working on three Portuguese cicadas ( Tettigetta
argentata , Tettigetta josei , and Tympanistalna gastrica ), demonstrating that the
neuromuscular structure used in the timbal cycle and the production of the echeme
succession (an uninterrupted burst of sound) are temperature dependent.
2.4 Elevation and Song Complexity
Elevation is an important factor that can modify the sonic ambient of species. Less
oxygen and more frequent and variable wind and breezes can affect the song
repertoires of species.
Harder conditions at higher elevations favor monogamy, a similar level of
parental care between females and males, and lesser variation in mating success
between sexes.
A comparative study on extant finches carried out by Snell-Rood and Badayaev
( 2008 ) demonstrated that species breeding at the lower elevations sang more
elaborate songs, producing a louder song when compared to their sister species
breeding at higher elevation (Fig. 2.3 ). The species breeding at lower altitudes have
longer songs with a greater number of notes.
These results demonstrate how the song repertoire of birds is affected by
environmental conditions and that this influences sexual selection. The structure
of a landscape is not the only proxy in determining the sonic ambience: other
factors connected with the availability of resources seem to have an important role.
Botero et al. ( 2009 ) have discussed an important issue related to climatic
unpredictability that seems to act as a driving force to the elaboration of signals
of quality in animals. In particular they have studied the song display in
mockingbirds using a pool of 1,738 recordings of mimids from which they
elaborated sounds from 29 species, using the following information:
1. Number of syllable types
2. Mean syllable type consistency
3. Tandem repetition index
4. Mean song duration (in seconds)
5. Mean syllable duration (in seconds)
6. Song rate (songs·min 1 )
7. Syllable switching rate
8. Syllable versatility
9. Mean number of syllable types in a song