We’ve seen it often enough; you’re out bird watching, looking at the deserted trees and bushes and wondering where all the birds are. Suddenly, they are upon you, lots of them, making it next to impossible to follow them all. It’s a foraging flock. But what is a foraging flock?

These congregations of several different species, often insectivorous, occur where there is an abundance of food. There has to be a ‘nuclear’ species as a basis for the flock’s hierarchy; with this species being central to the flock’s formation and movement.

Attendants come next. Attendant species often don’t join in on the activities until the flock’s activities enter their territory.  Titmice and chickadees often fill the roles of a ‘nuclear’ (‘core’) species in North America and are soon followed by nuthatches, creepers, woodpeckers, kinglets and New World warblers all of which are insect-eating birds. These flocks are seen mostly in the non-breeding season when birds come out of the secrecy of breeding and raising a family.

Downy Woodpeckers use chickadees as sentinels in the foraging flocks

The benefits are great for birds in these flocks, namely; the increased vigilance by more eyes, lowering the risk of predation. There could also be a rise in feeding efficiency; as bugs flee from one bird, they head right into the beak of another. Feeding together heightens the chance that someone will locate a rich feeding patch and birds benefit from the different abilities, such as a woodpecker’s strong beak.

Chickadees often act the part of the ‘nuclear’ species

Nuthatches will often join in on the action of feeding flocks.

But there are costs as well, for example, kleptoparasitism, or parasitism by theft. This is when one more aggressive bird, steals the food caught by another bird. The costs, however, are often outweighed by the more advantageous benefits.

Well, birds of a feather don’t always flock together, but they sure know who to flock with!

Posted by Matthew Sim