This is the time of year when the adult birds that arrived in spring are now combined with all the fledglings of the summer to create a peak population of birds in the northern hemisphere. The majority of the migratory bird species are now congregating and starting to head south. It might not be as apparent to us right now as the birdsong is not as constant, numerous or strong as what occurs each spring when birds are establishing territory. But when looking closely now in the backyard, especially on mornings when the overnight winds come from the north, there will be new arrivals quietly feeding in the trees on insects, seeds and berries.
In 2018 Cornell Laboratory of Ornithology published a four year study using weather radar data to determine the population of North American migrant birds in fall versus spring. The report states:
An average of 4 billion birds passed from Canada across the northern border of the U.S. in autumn, with 2.6 billion birds returning across the Canada–U.S. border in spring. Activity across the southern border was on an even grander scale: an average of 4.7 billion birds left the U.S. for Mexico and other points south each autumn, with 3.5 billion birds heading north across the U.S. southern border each spring.
In addition to being more numerous, fall migrants are often not in such a hurry to travel as they were in the spring to get on their territories to breed. They can linger and spend more time feeding to shore up for migration. They can be found flitting around the yard making soft chips as they pass through. The big difference is the duller colors on many of the migrants especially the warblers. These birds have molted out of their colorful breeding plumage into a very drab appearance making identifying them difficult. Roger Tory Peterson did a good job of warning birders of the frustration of identifying fall warblers with his two field guide pages of what he called “Confusing Fall Warblers”. And yes these fall warblers can be at times too confusing, confounding and complex to try and identify.
The warbler migration is just beginning here in central Minnesota. Hummingbirds from the north are coming in and will be jostling with one another at the feeders. Orioles, robins and rose-breasted grosbeaks are now present in larger numbers.
An immature Rose-breasted Grosbeak
Barn swallows
A sunset silhouette of cedar waxwings
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