There were a number of reasons that led me to choose my current place of residence.  Primary among them was the view of the Speed River and its thin strip of woodland habitat, where Osprey would come to fish and the songs of Red-winged Blackbirds and Yellow Warblers would sometimes trickle across the noisy street (important for someone accustomed to far more rural accommodations).  But another reason was its front-row seat to the late summer roosts at Silvercreek Park, and the spectacular natural display that accompanies it.

They begin to gather as early as July — blackbirds, grackles and starlings, though mostly the latter.  Sometimes several hours before dusk, hundreds of birds will appear on the hydro pylons, whistling and squabbling and socializing.  As summer wears on and the days grow shorter, the birds arrive later and later, taking available of as much foraging time as possible before returning to the evening roost.

By October, their numbers have climbed from hundreds into thousands.  They swarm about the pylons like insects, jostling for position on they hydro lines as each seeks to keep a well-defined buffer zone between themselves and their neighbours.  Large flocks rise up again and again and swirl in the skies above.  The noise becomes deafening.  Sometimes, a Cooper’s Hawk will cruise through, contributing to the mass unrest among the birds.

And then, quite suddenly, the entire flock will rise thunderously into the air.  The thousands of little black birds now become a single liquid organism, banking and flowing, splitting off and merging.  It’s an awe-inspiring and complicated pattern, and researchers have spent a lot of time attempting to model the behaviour.  As it turns out, you can closely simulate the dynamics of a starling flock by making each individual entitiy follow three simple rules:

1. Keep a minimum distance between yourself and your immediate neighbours (don’t run into anyone).
2. Match your speed to your immediate neighbours (keep up with everyone).
3. Constantly try to manoeuvre yourself into the perceived centre of the flock (protect yourself from predators).

It’s not clear why starlings perform these massive aerial displays outside of the breeding season.  The socializing that occurs at large roosts may be of immense benefit to individual birds — a bird that did not feed well that day could follow more successful birds out the next morning to a food source, and you are statistically less likely to be picked off by predators during the night when there are thousands of other potential targets all around you.  But the displays themselves (sometimes lasting until well after sundown) remain a mystery.  And when they are over, the entire flock spirals down into the trees, and all at once the roost becomes still and silent.  As if nothing had happened at all.

I don’t know why they do it, but I’m glad to able to witness this incredible phenomenon every evening.