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A tree swallow, one of the threatened species. (File Photo).CHUCK KIRMAN/Ventura County Star / AP

David M. Bird is an emeritus professor of wildlife biology at McGill University who has studied birds for five decades.

When I read the recent headlines that North America has lost nearly three billion birds over just the past five decades, I was not surprised. But I must admit it did depress me to a degree. That’s a lot of birds!

Before we lost the three billion, how many birds were there in North America? In 1963, Roger Tory Peterson, the godfather of North American bird-watching, estimated there to be between 12 to 20 billion at the beginning of that decade. Going with the conservative figure, that’s a quarter of our birds gone in just 50 years.

The loss of billions of birds on North American soil has happened before. To our everlasting shame, in the late 1800s, passenger pigeons, sometimes gathering in flocks of two billion birds, were wiped out to the very last bird by humans.

But the loss of these three billion birds over the past five decades is different. It’s happening to a wide suite of bird species, and for myriad reasons, some obvious and some more subtle. Of those three billion birds, the majority belong to 12 bird families and include songbirds such as warblers, finches, swallows and sparrows. Aerial and grassland insectivores, shorebirds and possibly seabirds are all in serious states of free fall and many of these birds were quite common only 50 years ago. Even the two most highly successful invasive species ever in North America, the European starling and the house sparrow, are declining today.

While the study, which was published in the prestigious journal Science, did not go into the reasons behind the decline, habitat loss and degradation must surely top the list. After all, can we really have almost eight billion humans inhabit the planet and expect not to have any major impact on the habitats of birds and other wildlife? Everywhere in the world, we are gobbling up the forests for building homes, turning grasslands into monocultural farmland useless for birds and eating up everything in the seas.

We banned the use of persistent organochlorine chemical pesticides – which stopped the eggshell-thinning that caused birds of prey to go almost extinct in the 1970s – but followed that act by creating, and then thankfully banning, even more poisonous pesticides such as the short-lasting organophosphates. Perhaps the most insidious human-designed chemical pesticides of all, though, are the neonicotinoids. They may not kill birds directly, but they are having devastating consequences for insects, a major food item for many birds. A major study, published earlier this year in the journal Biological Conservation, revealed more than 40 per cent of insect species are facing extinction. We cannot have birds without insects to feed them.

And then there’s climate change. Besides upsetting the delicate timing balance for migratory birds, they are killed by vicious storm systems, while rising sea levels and wildfires destroy their breeding, stop-over and wintering habitats.

And then there are the dangers closer to home. Not to pick on cat lovers, but most biologists today agree that pet cats kill more than a billion birds each year in North America. Glass windows on our houses and skyscrapers take out another hundred million annually.

So why should we even care about the birds? Besides contributing billions of dollars to our economy through the sheer love of watching and enjoying them, birds do a lot for humans. They eat pests, pollinate our plants and crops, disperse seeds; their eggs and meat feed us and their feathers keep us warm. They have even helped us win wars by teaching our military about flight, camouflage, sentry systems and acting as vital message carriers. Birds have saved human lives not just by serving as literal “canaries in coal mines” but also by warning us of environmental health hazards such as carcinogenic pesticides and industrial by-products.

But the situation is not hopeless. Our birds can rebound if we give them a chance. A single American robin, producing two broods of four young each year, and with all of them surviving to breed just as successfully, can leave almost 25 million descendants in a decade.

We must save natural bird habitats from the greedy fingers of progress. But there are some more immediate and simple things we can do on our own: try to consume local foods from sustainable sources, drink bird-friendly coffee, reduce the use of pesticides and other chemicals, substitute plastic bags and cups with reusable bags and drinking containers, control our pet cats and/or at least keep our next one indoors and find ways to reduce window collisions. Let’s not vote for politicians who weaken important bird-protection acts. Lastly, let’s find a way to give some time as a citizen scientist to organizations such as Bird Studies Canada – most of the data detailing the loss of the three billion birds came from volunteers.

We have always celebrated birds because of their intrinsic value. Who can deny that birds entertain us in so many ways with their beauty, their song and their flight? How many great writers, artists, filmmakers and even aviators and astronauts were inspired by these amazing creatures? In short, a world without birds will not just be a biologically diminished world but also an emotionally diminished one. And if we lose our birds, we will lose ourselves.

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