Back in the spring of 2010, as oil began pouring from a damaged undersea well in the Gulf of Mexico, the news media searched for stories that could illustrate the environmental damage for the American public. Just a few days into the Deepwater Horizon disaster, such a story ran, announcing the discovery and subsequent rescue of the spill’s first oiled bird, a Northern Gannet. That the discovery of the first oiled bird made national headlines shouldn’t come as a surprise. Any Google image search for “oil spill” will show you that photographs of dead and dying birds have told the story of virtually every oil catastrophe in recent history.

The reason for this is two-fold: First, as perhaps the only form of wildlife that nearly everyone sees every day, birds represent a very real connection between people and the natural world. And second, because of their sensitivity and ubiquity, birds are a particularly good indicator of the health of our environment.

Oil spill? Toxic river? Disease? Lack of food? Birds don’t speak human language, so they will usually tell us something is wrong in a very simple way: by dying, in large numbers.

While there would hardly seem to be a more absolute way of communicating with us, on occasion the birds go one step further: they will just disappear. One day they’re there; the next they’re gone.

This is how the birds will tell us about climate change.

It’s hard to see climate change. You don’t wake up one day, look out the window, and find it in your driveway. Scientists have tracked changes in temperature over decades, increases that we could have never perceived ourselves. Equally difficult for an ordinary person to perceive have been the gradual effects of these changes in temperature: the ebbing of polar ice, the rise of carbon dioxide in our atmosphere and the nudging rise in sea level.

Climate change is a gradual process, but steady. And it is slowly altering our environment in profound ways. Birds are feeling it.

A growing body of research has been tracking the gradual but steady impact of climate change on birds. For instance, the National Audubon Society has documented that more than half of the birds that winter in North America have shifted their ranges northward over the last 40 years in an effort to adapt to the changing climate. These shifts – averaging 37 miles, with some more than 200 miles – closely correlated to long-term winter temperature increases

While the research documents the shifts, it does not illustrate the difficulty birds face. Birds – from the giant Bald Eagle to the diminutive Allen’s Hummingbird – survive in an ecological envelope, a unique combination of habitat, food resources, temperature, and other important factors for which they are perfectly evolved.

Pushed into new geographical areas, will they find suitable habitat? Will they find food when and where they need it? Will they be forced to compete with other birds?

In the face of climate change, birds will not pile up on the beach. They will not fall out of the sky. They will not shout out their demise.

No, instead of those dramatic deaths, some birds – the lucky ones – will go somewhere else. Others will simply not make nests. Or they will have three eggs instead of seven. Or they will not successfully raise their young.

Around Audubon offices, we’ve grown tired of using the metaphor of the canary in the coalmine. But that’s the thing with some clichés – some are just too apt to avoid. Just as canaries dropping dead in their cages used to warn miners of dangerous gases underground, so too will birds warn us of the greatest environmental challenge of this century.

While certainly some of those warnings, like the canaries’, will come in form of dead birds, it is more likely that these warnings will come in a much quieter but no less haunting manner – through their absence.

And then those birds that we have come to love – the ones at our feeders, in our parks, in our nearby open spaces – will exist only in our memories.

Brigid McCormack is executive director of Audubon California