November is when the raucous calls of migrating flocks of blackbirds begin to punctuate the autumn woods, and noticeable vibrations can be felt as they lift off in unison creating a thunderous “whoosh.”
As the birds move off to another woodlot, their clucking calls can be heard as they sail overhead in a seemingly never-ending stream. But why do these individuals, preferring their own space during the spring and summer as they fiercely protect their chosen territories, gather together in breathtaking flocks in the fall and winter?
Flocking
Birds don’t congregate in large groups because they simply want to be social. Flocking is an important survival strategy. First of all, those giant flocks of “blackbirds” are normally made up of a variety of species including European starlings, common grackles, brown-headed cowbirds and red-winged blackbirds. Other species may enter the mix as well. Being included as part of a larger group comes with benefits, one of which is safety in numbers.
A single bird foraging for food on the ground or perched in a tree is an easy target for a predator such as a Cooper’s hawk. Turn that into thousands and the controlled chaos of the flock becomes overwhelmingly confusing to a predator trying to hone in on a single prey item. Furthermore, the many eyes in the flock act as an early warning system, making it impossible for a predator to approach unseen.
Working together instinctively as a group in this manner is referred to as “swarm intelligence.” This amazing behavior does not rely on leaders or hierarchy, but rather, is a consequence of individual birds responding to the behavior and movements of the individuals around them resulting in a ripple effect. In this manner, every member of the flock becomes involved in the decision making which leads to mass coordinated movements or intelligence. Individuals on the outside of the flock regularly rotate toward the inside where they can take a break from their vigilance and benefit from protection, warmth and rest. Swarm intelligence allows the birds to forage for food more efficiently and achieve productive rest on their overnight roosts.
The European starling, a non-native species that has become widespread throughout North America, sports a population that numbers in the hundreds of millions. Giant flocks dazzle with their mesmerizing murmurations. These movements, named for the humming sounds that emanate from the birds’ wings and voices are a sight to behold. As the birds wheel together in unison, they flip their bodies back and forth, resulting in a pulsing of light and dark feathers. The shape of the flock constantly changes, sometimes splitting into different groups, only to join up again. Most starlings do not migrate, remaining in their range throughout the winter. As the season progresses, more and more individuals join the main flock adding to its immense size.
Migratory birds also take advantage of flocking during their seasonal flights. The well-known ‘V’ shape seen in migrating ducks, geese and swans is a calculated, effective way of achieving successful long flights. By maintaining this shape, birds located further back in the formation benefit from the birds in front by utilizing the updraft and lift created by their wings, allowing them to conserve their energy. As birds at the front of the ‘V’ become fatigued, they drop back, rotating positions with other members. In this way, the birds give each other breaks, allowing for migrations that take them incredibly long distances and often over large bodies of water. The unique shape of this formation also allows the birds to maintain visual contact with each other, creating less stress.
Flocks of the past
When I begin to see the large flocks of blackbirds beginning to convene in the autumn, I can’t help but think about the passenger pigeons of days gone by. When Europeans discovered America, it was estimated that there were nearly 5 billion of these birds traversing the eastern half of the country, making up 40% of the total bird population. During their spectacular migrations, huge flocks of pigeons over a mile wide and traveling at speeds up to 60 miles per hour, darkened the skies for days on end, turning daytime to night as they blocked out the sun.
Although they traversed much of the eastern half of the continent during their migrations, their nesting territory encompassed the Great Lakes region, east to New York. Here they depended on huge expanses of mixed hardwood forests to support the need for their nests, roosts and food preferences. Passenger pigeons dined on a varied diet including seeds, acorns, beechnuts, chestnuts, berries and insects. One large nesting site in Wisconsin was said to cover 850 square miles and housed 136 million birds. It is hard to comprehend that a species that existed in such unfathomable numbers was completely extinct by the early 1900s due to man’s greed.
Christmas Bird Count
Last winter, while participating in the annual Christmas Bird Count in northeast Ohio, I happened upon an enormous flock of blackbirds making their way across the landscape. Never before had I witnessed this many birds at one time and it was estimated that there were hundreds of thousands, close to a million individuals, traveling and feeding together. To say that it was a spectacle is an understatement.
I tracked the flock for over a week and was alerted to an amazing bit of information. Turns out, the very location where this flock of blackbirds was calling home, was an area dubbed “the pigeon roost.” In 1820, an enormous flock of passenger pigeons arrived at this spot in Troy Township in Geauga County. “Many years’ occupation of this tract by pigeons, caused it to be the most fertile land in the township,” according to Pioneer History of Geauga County, 1880.
It’s hard to know if the presence of this flock of blackbirds at this location was simply a coincidence. The vast forests that once existed have long since been replaced by agricultural fields. Yet the fertility of this area obviously continues to echo a time when an enormous flock of passenger pigeons left their mark upon the land.
Video
To view the raw footage of this giant flock of blackbirds as it foraged at this historic location in January 2024, check out this link on my YouTube channel: https://youtu.be/UaMOENcDnXE.
