Naturalist and author Scott Weidensaul discusses the miracle of migration and how to protect our feathered friends

Nevermind the wildebeest of the Serengeti or the caribou of western Alaska; the greatest wildlife spectacle on Earth takes place over our heads twice a year.

Early May marks the high point of the spring bird migration season, when billions of birds around the world ranging from hummingbirds to eagles work their way north. Hundreds of millions of birds fly above and through Philadelphia via the Atlantic Flyway, essentially a bird superhighway following the Atlantic coast of North America.

In “A World on the Wing: The Global Odyssey of Migratory Birds,” Scott Weidensaul reveals the mind-blowing journeys birds make, as well as the threats that humans pose to these globe-spanning creatures. Weidensaul has devoted his life to studying and writing about birds. His work has taken him as near as the mountains of eastern Pennsylvania and as far as Denali National Park in Alaska. He talked with Grid about the amazing migrations of birds and what we can do to help them.

This conversation has been edited for length and clarity.

There are so many amazing bird migration accounts in “A World on the Wing” and in your earlier book “Living on the Wind” [1999]. Could you pick one that amazed even you, and that someone in Philadelphia could observe? The easiest thing to do would be to go down to Cape May in the springtime when you have shorebirds, including red knots that have spent the winter at the southern tip of South America, flying up to their breeding grounds in the High Canadian Arctic. They’re making about an 8,000, sometimes 9,000-mile, one-way trip from the furthest extent of the Western Hemisphere in the south to almost the furthest extent of the Western Hemisphere in the north. They stop off at the Delaware Bay for a couple weeks in May where they need to more or less double their weight, feeding traditionally on the eggs of horseshoe crabs. Of course the horseshoe crab population has been devastated in the Delaware Bay by 20 years of overfishing. The red knots have suffered badly. Their population is a fraction of what it was back in the late ’80s and early ’90s.

Thanks to new tracking technology, we’ve come to understand that the airspace of Pennsylvania is critical habitat for these birds.”

— Scott Weidensaul

They are never seen on the ground in Pennsylvania, but almost all of those red knots are over the airspace of Pennsylvania on their way flying north and west into the Central Canadian Arctic. So just in the last couple of years, thanks to new tracking technology, we’ve come to understand that the airspace of Pennsylvania is critical habitat for these birds.

And so as we make decisions about things like ridgetop wind turbines, that’s something that I think we need to at least take into account. I’m not saying we shouldn’t be putting wind turbines up there, but we shouldn’t overlook the importance of airspace as a critical habitat for a lot of these migratory birds.

You write about how technological advances have revealed so much about bird migration in recent years. Could you zero in on one of these advances: the MOTUS network of radio receivers? It uses two pre-existing technologies: highly miniaturized VHF [very high frequency] radio transmitters — I mean literally light enough in some cases you can put them on a butterfly — and then automated receiver stations that basically look like somebody forgot to take down their old-fashioned television antenna. All of the transmitters broadcast on the same frequency, but each one broadcasts a unique identification code.

So as they’re picked up by these receivers, the computer can tell whether it’s a white-rumped sandpiper that was tagged on the shores of James Bay, or a gray-cheeked thrush that was tagged in the jungles of Colombia, or a scarlet tanager or wood thrush that was tagged in the forest of northern New Jersey. It’s revolutionizing our ability to track most migratory birds.

What can people in cities like Philadelphia do to help migrating birds? Most birds, even the ones that are normally active in the daytime, migrate after dark. Cities draw migratory birds into them, literally like moths to the flame, due to the urban light pollution at night — especially in the fall, when most of the birds migrating are naïve young birds on their first migration.

Cities like Philadelphia have undertaken campaigns to get people to turn off their lights at night and control light pollution. That’s terrifically important because we lose probably about a billion birds a year in North America to building strikes and window collisions.

And we’re coming to understand the degree to which urban parks and greenspaces are vital liferafts for tens to hundreds of millions of migratory birds every year. So there’s a way to mitigate some of the damage, and that’s for us to start managing our parks and urban greenspaces for birds as well.

I’ll throw you a softball: what about our pet predators? For the love of God, if you have a cat, please keep it in the house. Cats are, pretty much without a doubt, the single most damaging human-related cause of bird death, somewhere between 2 and 4 billion birds a year. So more than windmills, more than lighted skyscrapers, more than speeding cars. All of that is additive on top of the natural dangers these birds face.

Anything we can do to reduce that human-related mortality is a plus, and cats ought to be the easiest kind of low-hanging fruit. All you’ve got to do is keep the door closed. And I don’t care if you don’t think your cat kills birds. Your cat kills birds — and voles, and lizards and all sorts of other little things as well.

It’s also true that dogs are surprisingly disturbing to birds. They don’t eat birds the way cats do. Birds can learn very quickly in parks that the people are just going to ignore them, but there’s a lot of research to show that even a leashed dog, even a well-behaved dog, is very disturbing. It scares the birds away.

I’m not suggesting that we ban dogs from our city parks. But on the other hand, if we are serious about creating an area that is good for birds, we might want to consider restricting dog walking in that part of the park.

Birds are everywhere and, especially if we make fairly small accommodations, cities can be good places for birds.

I know that it’s easy to drive people away if they feel like you’re attacking their pets. How do you challenge people without alienating them? Well, it can be hard because anything that is emotionally close for a person can become an emotionally polarizing issue. That’s why the third rail of bird conservation has always been cats. And unfortunately, as I say sometimes the choice has been made to just ignore the issue. I have probably put my foot in my mouth more than once in making my feelings known to people who I thought should know better than what they were doing.

I imagine the same is true for some of the powerful people you end up birding with, who have held high positions in government or in corporations that are involved in environmental destruction, the sort of people who go to the World Economic Forum in Davos every year. These are not the kind of people I usually run around with. We poor freelance writers don’t get invited to Davos. But I’ve been asked to hang around with the former chair of the Fed and the head of the World Bank. I’ve got the email for the CEO of TikTok. These are potential converts to changing things for the better for the environment. I think enlightened self-interest goes a long way, but also just the simple act of showing them a bird, really showing them a bird for the first time.

To see like a rookery full of nesting egrets, and ibis, and spoonbills, on the Southeastern coast on a spring day, when the alligators are bellowing, it can be a life-altering and perspective-altering experience. My job is to let the birds be the best ambassadors that they can be.