Isherwood Column: Autumn Swarms
By Justin Isherwood
Autumn means swarms. The term applies to a lot of animals and birds, and a distinct group/communal behavior. Krill and tuna swarm, wildebeests swarm, caribou, arctic seals, penguins, blackbirds, NASCAR, rock concerts, football fans swarm, as do farmers at auctions.
In Central Wisconsin swarm behavior effects cluster flies, Calliphoridae, a late summer phenomenon that’s really about midair mating. Which I tried to talk my wife into on several occasions but she thought it looked too hazardous. This what happens when a farmboy marries a city girl.
As for birds, pigeons swarm and blackbirds; redwings, cowbirds, grackles, starlings. Blackbirds gregariously swarm, where three, four, five species may be involved. This behavioral quirk of swarming isn’t odd because it is shared with other species but that this particular quirk is so darn precise.
Swarming is magical. If any act of nature suggests the universe has a Maker’s Mark, it is swarming. By appearance it seems a phenomenon impossible to pull off. Its speed and degree of precision hard to understand how it can possibly work, its performance seamless as it is effortless. It’s hard to conceive of animal flight being that coordinated, that fast. Hard to blame anyone at this juncture in throwing up their hands and saying “it works ‘cause God makes it work.” Swarming is that perfection of design, so detailed, so nuanced and correspondingly hard to fathom.
The scientific word for swarming is murmuration, if yet more technically correct, murmuration applies specifically to starling swarms never mind this is shared behavior with other bird species.
I invite the reader at this point to stop reading this column momentarily and Google murmuration. If you dig deep in the Oxford English Dictionary you will find the name for a flock of starlings is murmuration. The term rooted to onomatopoetic origins in Latin, to murmur. The trail of murmuration leads to murmur, thence to grumble, and the sound attached to starling flocks, in particular the sound of large flocks at roost. Their murmuring, muttering, grumbling noise, like a Lutheran congregation spreading salacious gossip.
Murmuration is now the broad term attached to the flight behavior of these same starling flocks as well as other species who perform like flight behavior. It is the nature of science to inject sobriety to behavior as might excite poets to hyperbole. Particularly of blackbird flight, that dazzling cloud, that swirling flock, that pulsating mass.
Science with its obligation to avoid ardor has converted starling murmuration to scale-free correlation, also known as high signal to noise ratio. High signal to noise business is precariously interesting, so much so I looked it up. High signal to noise ratio, aka S/N is commonly expressed in decibels. Acoustics it seems is all about S/N. A crowd in a room with a low ceiling has a low S/N ratio. You have to talk loud to be heard above the noise. Likewise my family at the Thanksgiving table has a low S/N ratio, particularly when the ratio of liberals to Tea Party activists is about even.
Applied to swarming, high signal to noise ratio refers to the fluidity of the motion coupled to the density of the flock. The closer that flock resembles a single entity the higher the signal to noise ratio. British research now suspects this behavior is predator-driven. The flight pattern of murmuration is designed to confuse predators such as owls, hawks and falcons, when a predator focusing on a single bird is interrupted by an ever-folding flight pattern. At one moment a bird is on the outside of the flock and thus vulnerable, at the next instant the flock has refolded that outside bird inside the flock. In insurance terms reducing the risk. In essence murmuring flight is just your average mutual insurance company, sharing that risk of the neighborhood sharp shinned.
Science has long been intrigued by murmurations; swarming flight has been photographed with high speed cameras, the film analyzed frame by frame to detail individual bird behavior. Current thesis is swarms follow the rule of seven, to the end a bird tracks with the next seven birds. The key to the swarm flight is, which seven? To the end these groups of seven are connected because every bird connects with another group of seven. And the swarm thus has its cohesion. To the end murmuring flight is the result of signal loss between these individual flight groups. It’s not that starlings or redwings intentionally fly enfolding flight patterns but the linkage of the seven member flight group to other interwoven seven member groups, none knowing which seven gains that fluidity of motion. The flock behavior is in essence a mathematical pari-mutuel. That insurance thing again, where every bird in that roiling mass is insured against risk.
It probably counts as blasphemy to reduce the creative genius of God, and birds to what a hometown insurance company does, but there it is. It seems blackbirds, starlings and pigeons invented Hardware Mutual Insurance well before P.J. Jacobs arrived. It’s still a good idea, meaning that signal to noise ratio thing.