The canary in the coal mine is, of course, the metaphor for a warning of impending doom, the tiny yellow birds taken into mines stopping their songs and often dying because of gas that could then kill the miners.
In “The Messenger,” Su Ryland’s eco-documentary, the canary is replaced by the world’s songbirds, billions of them, whose songs are gradually being silenced -- a bad omen not only for the birds but the planet.
Using captivating photography of the brightly colored little birds in flight to start the film, Ryland powerfully ends the picture with hundreds of tiny bodies arranged by species on a floor in a school with dozens of kids sadly looking on.
That, the film implies, could be the future of all of the dozens of species of songbirds that are already dwindling in number, with some going extinct.
The film spans the globe to detail the devastation -- birds flying into glass-covered buildings in Toronto, light pollution from the 9/11 memorial in Manhattan drawing in and confusing birds, trappers in France capturing a dwindling species for food, the destruction of habitat by energy development in the Boreal forest of Canada and even the predation of cats.
The cats prowling in yards and eating their prey are the only villains shown on screen. But, by implication, “The Messenger” points the finger at fossil fuel development and use for much of the threat to birds, and the planet, be it through the clearing of forests for oil pipelines or global warming.
Amid the warnings, “The Messenger” also conveys some amazing information, for example, showing via digital imagery the flight path of a purple martin that had been banded with a tiny digital signal chip as it makes its way from Pennsylvania to the middle of South America, covering hundreds of miles in a day.
It also details the work of academics and bird lovers in nearly every location it visits, studying bird behavior and trying to mitigate whatever threat is found in that area.
Some of those threats can be relatively simply solved. Turning off the lights that shoot high into the sky above New York City lets the birds find their way out, and, in Toronto, a requirement that little discs be placed on the windows of all-glass buildings has cut deaths by birds flying into them by 80 percent.
Other issues -- global warming, habitat destruction or the poaching of birds in France -- aren’t as easily addressed. But “The Messenger” subtly convinces that those threats must be addressed lest the songbirds serve as the canary in the coal mine for the Earth.