The magic of the fall migration

On Monday morning, as my son and I walked to the bus stop a little before 7, I was already hearing warblers. Specifically, I was hearing the flight calls these little songbirds give during migration. These are tiny, insect-like sounds that no normal person would notice or think came from a bird. As I walked back to the house, it was clear there had been an overnight arrival of migrant songbirds after a week or so of no action. I was witnessing a phenomenon known as a “morning flight” in my own neighborhood. This got me thinking about what morning flights are, and about some of the high-tech new radar tools researchers are using to study them. And more germane for you folks, they use these tools to forecast migration like meteorologists predict tomorrow’s weather.

A morning flight is not a typical thing to experience while birding around your house. This still poorly understood phenomenon is more associated with major coastal migration hotspots like Higbee Beach in Cape May New Jersey, Bluff Point in Connecticut, and Tadoussac Bird Observatory, Quebec, where these flights may involve thousands of birds. My flight was a few dozen birds – at the other end of the morning flight spectrum was May 28, 2018 at Tadoussac. That’s when Massachusetts birder Ian Davies filed what may be the most impressive checklist in the history of North American birdwatching - he tallied an estimated 700,000 warblers passing the once obscure Canadian bird observatory, including more than 144,000 Bay-breasted Warblers. Around here we get excited if we see one.

To understand morning flight it’s important to know that most songbirds migrate at night because it’s cooler, less turbulent, and there are no hawks to worry about, plus it gives them all day to refuel. Morning flight follows a nocturnal migration when birds may have drifted off course due to wind, so are reorienting themselves, often flying inland after coming in off the water. I suspect these warblers I saw passing my house first thing Monday morning had ended up over the Gulf of Maine overnight, then oriented to the elbow of the Cape at dawn and headed inland, eventually following the powerlines north through my neighborhood.

I never got to see what most of these warblers were, frustratingly, though I suspect some were Blackpoll Warblers. I did hear a few of the distinctive flight calls of Bobolinks, a unique member of the blackbird family that migrates a cool 12,000 round-trip miles from temperate hayfields to grasslands in Brazil and Argentina. With all the overhead activity, I thought I’d be armpit deep in new migrants at my sunny morning birding spot behind my neighbor’s house. It seemed I was right when the first three birds I put my binoculars on were a Rose-breasted Grosbeak and two Scarlet Tanagers, but things fizzled after that – most of the reorienting birds had not dropped in to stay, it seemed.

People noticed many years ago that mass migrations of birds and even insects were visible on Doppler radar, and this data has been used in many studies. But recent upgrades to the US Doppler radar systems now allow researchers to infer which way birds are facing while flying. The BirdCast site, a project of Colorado State University, Cornell, and UMass Amherst, now uses this more precise Doppler data to provide real-time migration data for every county in the US. According to this site, 400,000 birds passed over Cape Cod on Sunday night, which is high for here, and explains the morning flight I saw. And towards dawn, the site showed the birds went from heading due south to turning a bit west, consistent with birds coming in off the water and heading inland, as I saw.

This technology is mind boggling, even to me. Check it out for yourself – the BirdCast site predicted last night was another big night of migration, and it's not too late to get out there and see for yourself. The cool kids set up before dawn at places like Gooseberry Neck in Westport, the Gay Head cliffs, or maybe Morris Island in Chatham, but you might not have to go further than your own yard to catch a bit of migration magic. So head outside, tune your eyes and ears to the bird channel, and you might just get your own tiny window into a massive, hemisphere-spanning river of birds.