Sonic Patterns I: The Noise - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 150

Fig. 6.5 Call source level as function of background noise level in the killer whale (orca, Orcinus
orca ) (Reproduced with permission from Holt et al. 2008 )
frequency. In quiet conditions, the great tit was sensitive to frequencies between
2 and 4 kHz. In contrast to most other bird species, the great tit has low critical
masking ratio at high frequencies. This finding further demonstrated that great tit
communicates in a noisy environment using high-frequency vocalizations.
The airplane flyover is a source of unintentional noise that can affect animal
communities according to intensity, duration, and period of the day. The increased
level of such sound is strictly connected with a dramatic increase of air traffic
favored by low-cost ticketing solutions.
The effect of airplane noise and playbacks of low-frequency motorcycle sounds
has been examined by Sun and Narins ( 2005 ) on a frog chorus in central Thailand.
Three acoustically active species ( Microhyla butleri , Rana nigrovittata , Kaloula
pulchra ) reacted with a significant decrease of their calling notes, but Rana
taipehensis had the opposite behavior, increasing its calling rate. This last species
has been observed to emerge from the mixed chorus when the other species for
natural reasons were decreasing their activity. These results illustrate the complex-
ity of the effects of manmade sounds that produce a modulation in call rate and
assign, involuntarily, advantages to species that are stimulated to increase their
calls.
Studies conducted by Wood and Yezerinac ( 2006 ) have demonstrated that song
sparrows ( Melospiza melodia ) modify their vocalizations to reduce the masking