A night sky by Kristian Pikner, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons
On Sunday morning, October 12, I checked Cornell University’s BirdCast migration dashboard for Oakland Township to see how many migrating birds were flying overhead while I slept that Saturday night. Would you believe an estimated 7,000 to 14,000 birds! In Oakland County that night, scientists interpreting the weather radar indicated that an estimated 894,600 birds passed over while you and I slept on October 11. Imagine if we could have seen the sky filled with that many birds! And that’s not a record number in either case! It’s considered a “medium” night migration. The number changes quickly and by the time you read this, the numbers may be much lower. Most migrators have left by early November.
It occurred to me that you might be interested in seeing some of the birds that were navigating by starlight over your house and mine from August to October. I asked the skilled local photography team of Bob and Joan Bonin to share some of their outstanding bird photos for this piece. This couple works with incredible joy and dogged patience to take these beautiful photos and they were happy to share them with us. Thank you, Bob and Joan!
Evidently, a majority of birds, especially the small ones, fly at night. So I decided to refresh my understanding of the hows and whys of bird migration and share what I’ve learned with you.
Why Do So Many Birds Migrate During the Night?
Small birds choose to fly at night for at least three excellent reasons: 1) The air is calmer at night. Thermals (hot air) rising from sun- warmed earth during the day can make flying more turbulent. Flying at night means using less energy. 2) Their major predators – hawks, for example – aren’t as active at night. Thousands of hawks are migrating during the day at this time of year, riding the thermals on their way south. Best to avoid them. 3) Flying long distances with small wings can generate a lot of body heat and night migration makes for cooler flying.
How Do They Fly at Night?
Scott Weidensaul, author of A World on Wings: the Global Odyssey of Migratory Birds, explained that “Migratory birds grow fresh neurons before autumn migration” and scientists have correlated longer migrations with more neuron growth, presumably as an aid to navigation. Ornithologists now believe that migrators have specialized cells in their eyes with a protein called cryptochrome that allows birds to create a sort of navigation map by using moon and star light. For more details on this amazing process, see Weidensaul’s fascinating book or peruse my 2023 migration piece based on his book, called “Migration Miracles: How Migrating Birds Find Their Way to Us … and Survive the Journey. Migration really is miraculous!
So Which Birds are Leaving?
Be reminded as you watch these slideshows that these birds, striking as they are, are “wearing” their non-breeding colors! They save their fanciest outfits for the spring migration when they’re headed toward mating, but I’m always amazed at how diverse and colorful they look even in their winter plumage.
The Warblers: Some of the Smallest Migrators Flying through the Night
Our warblers are called the New World Warblers, or wood warblers and they have a few things in common. They are small, they sing and they spend most of their time in trees eating insects, though a few feed off of seeds or fruits on the ground. According to Cornell University’s subscription website, Birds of the World, recent evolutionary (phylogenetic) studies indicate that our warblers may have originated in Central or South America, but moved north in interglacial periods to find food and nesting sites. Looking at the migration maps for these birds on Cornell’s All About Birds website, it’s clear that most of them return to Central or South America each winter. Such tiny birds fly very far so they can feed off Michigan’s flush of insects each spring. Here’s a look at some of the warblers Bob and Joan saw in our parks from August to October.
As a birder, I appreciate that the Black-throated Blue warbler (Setophaga caerulescens) keeps the same stunning plumage year ’round. So does the female but she’s more gray and white with just blue tones. Hooray for simplicity! Photo by Joan Z. Bonin 
Bay-breasted Warblers (Setophaga castanea) forage avidly on spruce budworm caterpillars in their more northern breeding grounds. The budworms damage spruce trees, so the birds are just doing their part in stewardship, I guess! Photo by Joan Z. Bonin 
The Yellow-rumped Warbler (Setophaga coronata) shows a splash of yellow on its side and between its wings when perched, but displays the yellow rump feathers much more when it’s flying. Photo by Bob Bonin 
The dapper Black-and-White Warbler (Mniotilta varia) forages in the moss and bark of tree trunks. Photo by Bob Bonin. 
Black-throated Green warblers (Setophaga virens) aren’t usually seen at feeders, but we get to see them high in the trees during migration. Photo by Bob Bonin 
Blackburnian Warblers like this male (Setophaga fusca) fly from South America to Canada and back each year. No wonder these small birds can be blown off course fairly frequently! Photo by Bob Bonin 
The rarely-seen Oven Bird (Seiurus aurocapilla) is known for its tiny cup nest scooped from beneath the leaf litter and domed with leaves and twigs for camouflage. Its resemblance to a bulbous dutch oven gave it the name. Photo by Bob Bonin 
Cape May Warblers (Setophaga tigrina) have partially tube-shaped tongues which allow them to sip nectar from flowers in their tropical wintering grounds after having eaten mostly insects in Canadian forests during the summer. Photo by Bob Bonin 
The Common Yellowthroat (Geothlypis trichas) also keeps its breeding colors in the fall and winter. Males have a nice black mask and an easily recognized summer song, “Witchedy Witchedy.” Photo by Bob Bonin 
Magnolia Warbler (Setophaga magnolia) males and females look essentially the same during fall migration. In the spring, males sport black eyemasks and a “necklace” of black stripes. Photo by Bob Bonin 
Young Nashville Warblers (Leiothlypis ruficapilla) generally migrate south along the coast, so during the fall, we’re mostly seeing the adults who migrate more inland. This one looks to be extracting seed from a Sow Thistle seedhead (Sonchus oleraceus). Photo by Bob Bonin 
Palm Warblers (Setophaga palmarum) like to forage on the ground or in low shrubs, picking up fall grasshoppers or seeds while flicking their tails up and down. Photo by Bob Bonin
Sparrows, Vireos and Wrens: Fellow Sky Travelers in the Autumn Darkness
Sparrows: They’re not all brown!
It’s understandable that so many people think of sparrows as the ubiquitous little brown birds called House Sparrows (Passer domesticus) that noisily chirp on every street corner and sometimes in our parks. They aren’t native and aren’t warmly welcomed by birders because they can be destructive to the nests and young of other cavity-nesting birds like Eastern Bluebirds and Tree Swallows.
Our native migrating sparrows can be colorful, sing delightful songs, or just add a lot of hustle and bustle as they whisk about our fields and forests. Check out the slideshow below to meet a few now migrating to their wintering grounds.
The male Eastern Towhee (Pipilo erythrophthalmus) nests here for the summer and sings a very unsparrow-like, easily-recognized, quick song of “Drink your teeeeea! Photo by Bob Bonin 
A rare glimpse of a female Eastern Towhee in her lovely chocolate brown plumage with a warm, orange patch on her flank. Photo by Joan Z. Bonin 
The White-Crowned Sparrow (Zonotrichia leucophrys) has a dignified look with its bright black-and-white crown and gray face that makes it one of the easiet sparrows to identify. Photo by Bob Bonin 
The White-throated Sparrow (Zonotrichia albicollis) has a less-defined, striped crown but its definitive field mark for me is the white throat and the yellow spots (lores) near its eyes. Photo by Bob Bonin 
The Savannah Sparrow (Passerculus sandwichensis) frequents open fields and sings with a few quick notes,and a long, insect-like buzz combined with a low trill at the end. I first saw one while looking for the insect I was hearing! Note the yellow streak over the eye. Photo by Bob Bonin 
Lincoln’s Sparrows (Melospiza lincolnii) only pass through on migration and spend a lot of time concealed in shrubbery. Their peachy brown color distinguishes them from other sparrows, if you can come across one! Photo by Bob Bonin
Vireos and Wrens: Listen for Their Songs!
Here’s a collection of first class songsters! Many vireos and wrens sing with gusto most of the day in the spring breeding season. They aren’t flashy birds but they bring to the ear the pulse of a spring or summer day with bubbly songs, long ones and short ones. Meet these small birds with delightful voices as they head south in the starlight.
The Northern House Wren’s (Troglodytes aedon) song is a rush of burbling notes that ends in a trill. They zip from tree to shrub around us on any summer day. They’re headed for the deep South, Florida or Mexico. Photo by Bob Bonin 
Marsh Wrens (Cistothorus palustris) are seldom seen since they sing their songs from deep among the reeds in marshes. But Bob saw this one in its typical spread-leg stance when singing. Photo by Bob Bonin 
The song of the shy Sedge Wren (Cistothorus stellaris) is a few chips and a short trill from a wet field or a shallow marsh. It’s rarely seen, too, but Bob did it again! Photo by Bob Bonin 
The short, up-and-down song of the Warbling Vireo (Vireo gilvus) gives its location away. Though high in the trees, it forages slowly so sometimes I get to see one. Bob caught one in mid-warble! Photo by Bob Bonin. 
The Red-eyed Vireo (Vireo olivaceus) was once called the “preacher bird” probably by some scallywag who didn’t like long sermons! Its short but repetitive song of one of these vocalists can be heard thousands of times in one day. It’s on its way to the Amazon! Photo by Bob Bonin 
The Blue-Headed Vireo (Vireo solitarius) sings a two-up, two down song fairly slowly . So sometimes, if you’re persistent like Joan was, you can find one above you. The bluish/gray head looks more blue in the shadows, more gray in bright light. Photo by Joan Z Bonin 
The Yellow-throated Vireo (Vireo flavifrons) stands out among its kind for its bright yellow breast and yellow “spectacles” around its eyes. Its 2 or 3 note song is done verrry slowly. Photo by Bob Bonin
Other Small Traveling Companions Heading South
Many other small birds accompany the Warblers, Sparrows, Wrens, and Vireos at night. Here are just a few that Bob , Joan and I couldn’t resist choosing.
In the late summer, the Indigo Bunting male (Passerina cyanea) begins to molt his gorgeous summer feathers which have little structures that reflect only blue light. They replace them for the winter with brown plumage, with just touches of blue on the wings or tail. Photo by Bob Bonin 
The more modestly “dressed” female Indigo Bunting also heads for Mexico, Central America and Belize. Indigo Buntings can sometimes be seen in large flocks as they migrate, but at that time, it’s tough to tell the males from the females! Photo by Bob Bonin 
A favorite of mine, the Ruby-Crowned Kinglet (Corthylio calendula) is tinier than warblers and sparrows. Many winter in Florida, some head for Mexico on those tiny wings! The ruby crown under the head feathers pops up in spring when the males get excited. Photo by Bob Bonin 
Bob caught this juvenile Ruby-throated Hummingbird (Archilochus colubris) in flight this fall. Amazing photo! By now, most will be on their way to Central America. Photo by Bob Bonin 
Look at that Ruby-throated Hummingbird’s tongue! Couldn’t resist this action shot by Joan Bonin! 
The birders saw this worn-looking Olive-sided Flycatcher (Contopus cooperi) in a typical spot. These birds love to search for insects on dead trees (snags.) This one needs to fatten up. It’s got a long trip ahead, perhaps as far south as Bolivia! Photo by Bob Bonin
Birds Going…But Also Coming
For this post, we’ve concentrated on the smaller birds that wing their way south while we sleep through longer nights. But bigger birds – herons, egrets, cranes, and of course all those amazing shore birds, geese and ducks are migrating south too! The hawks are filling the skies during the daytime, riding the rise currents of warm air. Maybe part of the wistful feeling we have in the autumn is connected to being left behind by all these beautiful summer visitors.
But Bob, Joan and I hope to do another post in the next few months about the birds that travel to Michigan to spend the winter with us and our year ’round birds. Many of them arrive from northern Canada and even the Arctic. They evidently find Michigan relatively balmy in the winter months compared to their breeding grounds! After all, plentiful food can be found here during the winter: nuts on or below the trees, seeds in the fields, berries and other dry/frozen fruits in the hedgerows, and frozen insect eggs, caterpillars or pupae hidden in tree bark and leaf litter left by the bounty of a Michigan summer. And then there are those those well-filled bird feeders of ours filled with fatty sunflower seeds and more! Quite a tempting feast for “snow birds” visiting from the far north.
For now, though, we wish “Bon Voyage” to our summer avian visitors. We look forward to seeing them colorfully dressed and full of song to charm their mates when spring greening begins again.