Biologists and volunteers in Milford spent Thursday tagging endangered purple martin birds with tracking bands in an effort to monitor air quality.

The Connecticut Audubon Society at Milford Point says the bands may help scientists figure out why the birds' population is in decline.

The bands will allow biologists to see where the purple martins migrate to, how long they live and where they've made their different colonies.

The birds had nearly disappeared from Connecticut, although the species was recently taken off the threatened species list due to conservation efforts. 

The birds are an indicator of air quality, according to Milan Bull, of the Audubon Society, and their declining numbers could be a red flag.

"In an ecosystem, every little animal matters," explains Megan Carroll, one of the volunteers.

Similar efforts to tag young purple martins are scheduled down the shoreline next week.