A flock of pigeons wearing mobile phone backpacks are to be used to monitor air pollution in California.

About 20 pigeons will each carry a mobile phone with a GPS tracking chip and air pollution sensors, reports New Scientist.

Data will be sent back via text messages to a so called pigeon 'blog' on air quality.

And miniature cameras tied around the birds' necks will post aerial pictures of trouble spots.

Beatriz da Costa, a researcher from the University of California at Irvine, and two of her students came up with the idea.

They built a prototype of the pigeons' equipment, containing a mobile phone circuit board with SIM card and communication chips, a GPS receiver and sensors capable of detecting carbon monoxide and nitrogen dioxide.

The pigeons are to be released in August into the smog-filled skies over San Jose in California.