Pollution is an attractive proposition for male birds. It helps them attract females by singing better. The flip side--it may result in their population decline. Researchers in the uk have found evidence of pollution increasing the size of "song centre" in the brain but damaging birds' immune system. The study was conducted on European starlings, a migratory song bird species, whose population has suffered a 50 per cent decline in the past 40 years.
The starlings under study were found to forage for food on toxic filter beds of sewage treatment plants. The filter are rich in organic sediments and support a large community of worms. The researchers found that the toxins that worms feed on acted as estrogen in the bird's brain.
It helped birds produce better sounds. But it also caused disruptions in the endocrine system that affected neural development, immune system and behaviour of male birds. It also decreased reproductive success.
"Females prefer the song output from males exposed to a mixture of endocrine disruptors despite the fact that such males are immuno-suppressed. If female starlings bias their reproductive investment towards males in poor physiological condition then hatchling rates could decline with detrimental consequences at the population level," the authors noted in the study published in the February 27 issue of PLoS One.
According to Surya Prakash of the School of Life Sciences, Jawaharlal Nehru University, Delhi, hormone levels also undergo changes due to air pollution. "The diurnal rhythm of song birds gets disturbed, especially in places where there are more diesel fumes and fewer trees. The egg quality is poor and in less numbers," he said.
Anand Arya, a bird watcher from Delhi, agrees. "In the Okhla sanctuary, some birds such as pied bushchat, red munias and prinias have been very vocal in the past but this year they have been seen in less numbers," says Arya.
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