Migration
The daylight hours have dwindled, the crescendo of summer heat tapered back to a murmur, and the birds have begun their mass exodus once more. An incredible 380 species of land birds, raptors, shorebirds, waterbirds, and waterfowl fly through Michigan skies each fall as they migrate to their wintering grounds, many of them traveling the two aviation superhighways—the Mississippi and Atlantic—that intersect over Michigan.
Weightless and lithe as figure skaters skimming across the ice, these birds make their flights look easy, but don’t be deceived: migration is a harrowing journey, one that many birds don’t come out of alive. One study on black-throated blue warblers found 85% of annual mortalities take place during their three months of migration. Another study found the mortality rate of three raptor species is six times higher during migration than stationary periods. In short, migration is a dangerous venture.
And it’s only getting worse. Half of the world’s bird species are currently in decline. One in eight are under threat of extinction. The birds under threat aren’t just those in faraway rainforests or on tropical islands, either: White-throated Sparrows across the US and Canada have declined by 93 million individuals over the past 50 years. Six in ten Wood Thrush have disappeared in the same time. In total, since 1970, the US bird population has decreased by nearly 2.9 billion.
But birds evolved 100 million years ago (give or take, depending on the species), and have clearly been able to survive up to this point. Why the sudden plummet?
In a word: light.
By and large, birds are nocturnal migrators. Pick up a pair of binoculars during the migration season and aim it at a lumbering moon, and you’ll be able to watch the shadowy silhouettes of small, sharp-winged bodies flittering across the sky. From an evolutionary standpoint, nocturnal migration makes sense. In addition to the cooler temperatures and stable atmosphere that night offers, many species rely on celestial navigation to find their way to and from their wintering grounds, using the stars as a compass much like the sailors of antiquity.
What was once an evolutionary advantage though has become a liability as the night sky is increasingly inundated with artificial light. Traffic lights, streetlamps, backlit billboards, lights from homes and buildings… Whatever the source, birds veer off course to pursue illuminated areas, wasting the precious, finite energy they need to complete their journeys.
There are luckily steps individuals can to mitigate the risk of disrupted navigation, including lowering shades and turning off exterior lights during fall and spring migration. Those who want to learn more about when exactly the skies are busiest can visit the Audubon Society’s website for an interactive map detailing peak migration times. A migration forecast is also available on birdcast.com.
Outside the hardships of migration, birds face a litany of other year-round threats. An estimated 2.4 billion US birds are killed by housecats annually. Another one billion die each year from window collisions. These losses are only amplified by habitat degradation and fragmentation.
With the swell of birdsong falling silent, now is perhaps the best time of year to consider what it would be like to live in a world absent of birds—and why it’s so important to take steps to protect them.
Although many cat owners understandably worry that confinement to the indoors will affect their pet’s health, most experts agree that indoor cats live healthier, longer lives than their free-roaming alternatives, while saving birds to boot; leash-controlled walks and confined outdoor areas are good alternatives to letting cats roam free. Homes and buildings can also be made safer for birds by installing screens or applying film to windows. Avoiding pesticides, reducing plastic use, and drinking bird-friendly coffee also helps.
Weightless and lithe as figure skaters skimming across the ice, these birds make their flights look easy, but don’t be deceived: migration is a harrowing journey, one that many birds don’t come out of alive. One study on black-throated blue warblers found 85% of annual mortalities take place during their three months of migration. Another study found the mortality rate of three raptor species is six times higher during migration than stationary periods. In short, migration is a dangerous venture.
And it’s only getting worse. Half of the world’s bird species are currently in decline. One in eight are under threat of extinction. The birds under threat aren’t just those in faraway rainforests or on tropical islands, either: White-throated Sparrows across the US and Canada have declined by 93 million individuals over the past 50 years. Six in ten Wood Thrush have disappeared in the same time. In total, since 1970, the US bird population has decreased by nearly 2.9 billion.
But birds evolved 100 million years ago (give or take, depending on the species), and have clearly been able to survive up to this point. Why the sudden plummet?
In a word: light.
By and large, birds are nocturnal migrators. Pick up a pair of binoculars during the migration season and aim it at a lumbering moon, and you’ll be able to watch the shadowy silhouettes of small, sharp-winged bodies flittering across the sky. From an evolutionary standpoint, nocturnal migration makes sense. In addition to the cooler temperatures and stable atmosphere that night offers, many species rely on celestial navigation to find their way to and from their wintering grounds, using the stars as a compass much like the sailors of antiquity.
What was once an evolutionary advantage though has become a liability as the night sky is increasingly inundated with artificial light. Traffic lights, streetlamps, backlit billboards, lights from homes and buildings… Whatever the source, birds veer off course to pursue illuminated areas, wasting the precious, finite energy they need to complete their journeys.
There are luckily steps individuals can to mitigate the risk of disrupted navigation, including lowering shades and turning off exterior lights during fall and spring migration. Those who want to learn more about when exactly the skies are busiest can visit the Audubon Society’s website for an interactive map detailing peak migration times. A migration forecast is also available on birdcast.com.
Outside the hardships of migration, birds face a litany of other year-round threats. An estimated 2.4 billion US birds are killed by housecats annually. Another one billion die each year from window collisions. These losses are only amplified by habitat degradation and fragmentation.
With the swell of birdsong falling silent, now is perhaps the best time of year to consider what it would be like to live in a world absent of birds—and why it’s so important to take steps to protect them.
Although many cat owners understandably worry that confinement to the indoors will affect their pet’s health, most experts agree that indoor cats live healthier, longer lives than their free-roaming alternatives, while saving birds to boot; leash-controlled walks and confined outdoor areas are good alternatives to letting cats roam free. Homes and buildings can also be made safer for birds by installing screens or applying film to windows. Avoiding pesticides, reducing plastic use, and drinking bird-friendly coffee also helps.