Melbourne, Oct 22 (ANI): A new study has shown that birds living in an urban environment evolve their songs to talk through the noise.
For the study, Dr David Luther of the University of Maryland and Dr Luis Baptista of the California Academy of Sciences examined three adjacent dialects of the native White-crowned Sparrow over a 30-year period, from the late 1960's to 1998.
They hypothesised that the growth of urban sprawl in the San Francisco area would have become a "selection pressure" on the birds.
"Urban noise, which is louder at lower frequencies increased during our study period, and therefore it should have created a selection pressure for songs with higher frequency," ABC Online quoted the study, as saying.
During the study, the researchers made recordings of the birds in 1969, 1970, 1990 and 1998 and compared their minimum frequency.
The recordings proved their hypothesis correct.
The researchers found that of the three dialects, known as SF, P and LM, initially recorded in 1969, only LM and SF remained in 1998.
Ethologist Professor Gislea Kaplan of the University of New England said that the P dialect had the lowest frequency.
During the same time period, the higher frequency SF dialect increased from 29 percent to 95 percent.
"In response to high levels of low-frequency ambient noise, urban birds have songs with higher frequencies," the authors said.
Kaplan said that results of the study not only showed that the lower frequency dialect P become extinct in the region, but that the minimum frequency of the remaining dialects LM and SF increased compared to the their rural counterparts.
The current theory on how birds and other animals communicate suggests they try and talk to each other at a frequency level that cuts through the ambient noise, she said.
The findings have been published in the latest edition of the Proceedings of the Royal Society B. (ANI)