Sonic Characteristics of the Landscape - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 30

important as gusting, especially when transmitters and receivers are close to the
ground and function in the frequency considered. The maximum attenuation close
to the ground pertains to the frequency between 200 and 500 Hz.
The dominant source of pressure fluctuation at a microphone is represented by
the intrinsic turbulence in the flow (Morgan and Raspet 1992 ). The noise produced
by wind is a problem for collecting biophonies but on the other hand is important
information on environmental dynamics. Rustling leaves can be an important cause
of background noise over a wide range of frequencies.

2.3 Climatic Patterns and Sounds

Very few papers are concerned with climatic changes and their consequences on the
sonic ambience and in particular on the acoustic performance of animals. It is
expected that change in climate conditions has effects on sound transmission and
consequently on vocal communication. Evidence on the relationship between sonic
patterns and climate pertains to indirect effects of climatic shifts and calling
phenology.
For instance, the calling phenology of frogs has been documented to be changed
during the past century, as reported by Gibb and Breisch ( 2000 ) near Ithaca, New
York. Four species of frogs have been observed to be calling 10-13 days earlier
than in the period 1900-1912. Two species have unchanged phenology, but none of
the species is calling later in the season. This observation indicates that the global
warming has produced biological responses in these populations (Table 2.1 ).
Different effects can be predicted: the rise in temperature increases the absorp-
tion of lower frequencies but enhances the higher frequencies, although this effect
co-varies with atmospheric pressure and relative humidity.
The changes of climate modify the phenologies of plants, and an early leafing
can modify the sonic ambience during the vocal performance of many species of
birds. A comparison of height at which birds select song posts, carried out in the
period 1986-1989 and 2010 by Moller ( 2010 ), demonstrated that birds have
increased the height at which they sing. In this period, spring and summer

Table 2.1 Climate warming and calling phenology of six frogs near Ithaca, New York,
1900-1999
Average first calling date
Species 1900-1912 1990-1999 Mean change (days) p

Spring peeper April 4 March 20 13.6 0.038

Wood frog April 9 March 29 13.0 0.007

Bullfrog June 5 May 22 11.5 0.098

Gray treefrog May 4 April 14 10.5 0.030

American toad April 18 April 11 1.5 0.303

Green frog May 10 May 16 5.5 0.808

Reproduced with permission from Gibb and Breisch ( 2000 )