Over the years, the eastern meadowlark has become increasingly difficult for Maine birders to find. Credit: Courtesy of Bob Duchesne

The news dropped like a bombshell. Over the past 50 years, 2.9 billion birds have disappeared from North America. One out of every four birds is gone. A team of international scientists under the auspices of the Cornell Lab of Ornithology analyzed the data and released their findings this summer. What on earth happened?

It’s complicated. The simplest answer is that humans just take up a lot of room. Fifty years ago, the U.S. population barely topped 200,000,000. Nowadays, there are more than 329,000,000 of us. It’s not just the expansion of subdivisions to accommodate all the extra people. It’s also the amount of land converted to provide food and energy to meet the needs of an expanding population. Our appetites have even reduced wintering habitat for many of our songbirds. Our yen for coffee has led to the clearing of tropical jungles, just as our hunger for hamburgers has resulted in the conversion of South American grasslands to pastures. Habitat loss is likely the biggest factor in the decline, but it’s not the only one.

Think back to those warm spring evenings when a hatching of insects so fouled the windshield that you needed to turn on the wipers. Bugs pinged off the hood like sleet. When was the last time you saw that? Between wetland drainage and increased pesticide use, there’s a lot of bird food that simply disappeared from the continent.

Some of the other human-induced impacts are well-known, yet well-hidden. Over a billion birds per year are killed by outdoor cats, but it’s hard to recognize the cumulative effect when little Whiskers leaves just one dead bird on the doorstep in the morning.

Windpower gets a disproportionate amount of blame, considering that birds also collide with skyscrapers, communication towers and high tension lines. Most songbirds migrate at night, unaware of obstacles above the treetops. We’re not going to stop building things high into the air, so it’s important to continue research on ways to reduce collisions up there.

The alarming Cornell report is only as good as its supporting data. Fortunately, Americans have been doing breeding bird surveys for half a century, and Christmas bird counts for twice that long. One tool has become increasingly valuable: weather radar. There are 143 stations across the country. The same system that detects raindrops in the air can detect birds in the air. On migration nights, whole clouds of flying birds become visible … and countable. Regrettably, the radar tally shows a decrease of 14 percent over just the past 11 years.

Grassland birds are hardest hit. Over half of them have vanished nationwide. The conversion of farmland to subdivisions accounts for much of the habitat loss. Early haying in the east is a major factor. In Maine, the eastern meadowlark has nearly disappeared. Bobolink numbers have plummeted. In the Midwest, America’s appetite for ethanol has converted miles of grasslands to cornfields.

Shorebird populations have shrunk by a third, decimated by multiple threats. Rising sea levels due to climate change are inundating nesting grounds in the arctic. Warmer temperatures have also led to an increase in predators moving into their colonies. Coastal development has degraded migratory feeding areas.

The shorebird decline is particularly noticeable in Maine. Because of our high tides and extensive mudflats, Maine is a major stopover for migrating shorebirds. Sadly, where I used to see thousands of shorebirds, I now see hundreds, and sometimes not even that.

Birds of the northern spruce forests have taken a major hit. One third of them are gone. Birds of the western forests are nearly as bad off, losing 27 percent of their populations. Even in the east, our forest birds have declined by 17 percent.

What most scares the bejeebers out of ornithologists is the decline in common birds. Almost half the red-winged blackbirds are gone. A third of Baltimore orioles, dark-eyed juncos, and white-throated sparrows have vanished. Blue jay populations have plummeted by a quarter. An estimated 862 million sparrows and 618 million warblers are lost. We’ve worried about endangered species for so long, we failed to comprehend how badly unendangered species were doing.

The sky isn’t falling. Some of the decline is in species that we wanted to decline, such as European starlings and house sparrows. Some of it is explained by natural variation, such as species that rise and fall with spruce budworm outbreaks. Raptors and waterfowl are doing better. We just need to give some serious thought to how the 329,000,000 of us can avoid crowding all other life off the planet.

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.

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Bob Duchesne, Good Birding

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.