Jan 11 2008
At rush hour last night, a river of crows flew over Fifth Avenue and perched in the trees on Wilkins. That event and last week’s robin roost prompted me to think about flocking behavior.
We’ve all noticed that birds flock in winter. It turns out that flocking is usually a trait of social species, such as crows and parrots, and species whose food sources are abundant: omnivores like gulls and starlings, seed-eaters like blackbirds and finches. But why to they do it?
The first reason is defense. It’s harder to be caught unawares if you’re in a flock with many watchers and it’s statistically quite safe. At the robin roost we heard a pair of great-horned owls but each owl will catch only one bird per night, leaving an individual robin with a 0.002% chance of becoming an owl meal.
Another flock advantage are the many eyes searching for food. If the food source is abundant – a seed field or a landfill – everyone gets a meal. Obviously, flocking doesn’t work for birds like red-tailed hawks who catch their prey by stealth.
Social species enjoy flocks. Crows get smarter by being with each other. As Candace Savage said in Crows: Encounters with the Wise Guys: “Nothing is more intellectually challenging than living in a social group, surrounded by a bunch of other animals that are sharpening their wits on you.”
The most spectacular flocks are made up of starlings who wheel in unison without an apparent leader as in the “cloud” pictured here. Not all birds fly in a tight formation like this. When it comes to flocking, starlings are the champs.
(photo by Tom Pawlesh)