Last spring, I found myself entranced by a pair of red-tail hawks building a nest in Riverside Park, just a few blocks from my apartment in New York City. Unfortunately, despite the efforts of their parents and the best wishes of many hawk watchers, the three hatchlings didn't survive, probably because of poison.

It's certainly not unusual for young birds to succumb to the many threats -- natural and manmade -- found in the urban wilderness. But this morning, on the first day of spring, a new report had me thinking of those baby hawks and their fate again.

According to an analysis of 40 years of data, bird populations in the United States are declining at an alarming rate due to climate change, habitat destruction, invasive species and other environmental forces.

U.S. Interior Secretary Ken Salazar called the disturbing news a "clarion call" for action. "If we move forward with a new ethic of conservation, we will be able to restore bird populations," Salazar said at a news conference.

Nearly a third of the 800 species of birds in the United States are endangered, threatened or in decline, according to the report, which is the most comprehensive ever undertaken of birds in North America. But more than that, the decline of birds is a warning sign about the overall health of our environment -- or lack thereof.

Birds are literally the "canary in the coal mine," Salazar said.

Among the report highlights, as reported by Scientific American:

• U.S. grassland bird species have declined 40 percent.
• Birds in arid lands have declined 30 percent.
• 39 percent of U.S. birds restricted to ocean habitats are declining.
• Some coastal shorebirds are doing well, but many face habitat losses and dwindling food supplies.
• Birds in Hawaii face a conservation crisis, with many species on the edge of extinction.

Not all of the news was bleak, however. In some places where conservation measures have been adopted, bird populations are rebounding and even thriving. "We need to protect habitat and aggressively attack climate change with renewable energy," said John Flicker, president of the National Audubon Society.

One place where birds need protection right now is in Canada's ancient boreal forest, where billions of birds -- more than half of North American species -- build nests and raise their young each spring. By the end of summer, they'll head south and snack onbirdfeeders in U.S. backyards.

For many species, the Canadian forest -- teeming with lakes, river valleys and wetlands -- is the only nesting place they've ever known. Yet as NRDC reported last year, attempts to mine and drill the Alberta tar sands for fuel are destroying and fragmenting this precious habitat, resulting in the loss of millions of birds.

You can find out more about the Canadian forest and take action to protect birds from dirty fuel development at NRDC's new Save BioGems site. My hope is that fewer birds have to face the fate of those three hawk hatchlings that I watched perish last spring.

Photo: One of the Riverside red-tails lands on its nest. By Scott Dodd/via Flickr