Birds of a Feather?

“Birdes of a feather will flocke togither.”
The Dictionarie in Spanish and English, compiled by English lexicographer John Minsheu, 1599

Sometimes, when I head into the backyard in seach of peace and quiet, I get more that I bargained for. Way back in the day, we began to notice periods of quiet, when wandering back there in our mini-woodland was like meandering through a held breath, when the trees were empty of birds and the only noise was the city-rush of traffic off in the background. Maybe a rustle of leaves, if a breeze happened by, but no chirps, twitters, tweets, or cheeps to be heard. Sometimes even the usually ceaseless tumble and buzz of insects would pause for a bit.

These hiatuses were, I’m happy to report, temporary states of affairs, and if we waited them out we would soon see a flicker of motion at the edge of vision, then another, then another, until the trees and feeders and watering holes came alive again and the circus resumed.

Sometimes, rarely, careful searching during the pauses might reveal the presence of a hawk, whose hungry gaze enforced a precautionary silence while the raptor lurked, but those times were the exceptions, not to mention the equal likelihood that the presence of a hawk, or wandering cat, would trigger cries of alarm and harassment until the predators gave up and moved on.

For years, I just chalked these calm periods up to coincidence, thinking that everybody out there had their quiet times and sometimes everybody had them at the same time by chance, like conversational lulls at a house party.

But maybe not.

Turns out that birds aren’t always those independent little flashes of color and charm that they might seem to be. They don’t always stay true to their own little patches of leafy turf and hang out with buds of their own species. Sometimes they like to party and forage wide—and in groups of several to many different “feathers”, making up what are termed “mixed species flocks”.

I first got suspicious when I began noticing, often in quiet interludes of lazy watching out back, that the calm pauses could end fairly quickly, with one or a couple birds showing up, then more following hard on their tailfeathers, until the yard was active again with many birds of different kinds. I noticed that the first birds to show up were almost always tufted titmice, followed pretty quickly by Carolina chickadees. Then came more—including, but not limited to, house finches, downy woodpeckers, red-bellied woodpeckers, nuthatches, goldfinches, and cardinals, among others, depending on season, time of day, etc. Bluejays and Carolina wrens, sometimes, or robins (not reliably).

So, one day I typed “mixed species flocks”, which seemed like a pretty good place to start, into my search engine and, bam!, the floodgates opened, along with my eyes. Like this, for example:

“It is not uncommon to find birds of several species flocking together. One reason may be that such flocking increases the number of eyes and ears available to detect predators and may confuse them as many individuals flee at once. Also a mixture of species can take advantage of different abilities. Just as nearsighted zebras with keen hearing associate on African plains with species such as wildebeest and giraffes with keen eyesight, so nearsighted gleaning birds such as Red-eyed Vireos move in groups (on their tropical wintering grounds) with farsighted salliers like Yellow-margined Flycatchers. The former lose some prey to the latter, but apparently are more than compensated by the latter’s early detection of approaching danger. Similarly, it has been shown experimentally that chickadees and titmice are used as sentinels by Downy Woodpeckers foraging in mixed-species flocks.”

Chickadees, titmice, and downies! Wow, did I call it or what? Not only that, but the article (and others) identified titmice as among the leaders of these roving bands. Considering that both titmice and chickadees have distinctive alarm calls, this shouldn’t have been a surprise. So, when I thought our yard had just gotten quiet, it was because the party was on the move in other yards around the neighborhood. Some observers found “that chickadee/titmouse-led flocks are irregular in their movement, with no clear pattern of speed or direction. In a particularly careful study of flock movements, Powell (1979) found that flock movement approximated a random walk with a bias toward forward motion”. Just a stroll through the ‘hood to rustle up a snack!

Sentinel duty, however, may not be the only benefit of mixed flocking. The ‘nuclear species”, like titmice and chickadees, that often make up the core of these flocks also tend to be generalists in their foraging behaviors, searching up and down trees and other vegetation at a variety of heights for their lunch. Because they disturb insects as they move around, other birds tag along, hoping for an easy snatch.

Also, birds that use different kinds of hunting/foraging patterns often scare up prey that other birds who do it differently might miss. This is sometimes called “commensal feeding“. A woodpecker or trunk-gleaning bird might scare up an insect hiding under a leaf, which could be grabbed by a chickadee, or vice-versa, and who’s going to miss a purloined bug here or there? Really.

As usual, though, the no-free-lunch law kicks in. There can be downsides to all this diversity. Seems that these very active and noisy flocks might not just harvest more food, but also unwanted attention. It might be that flocks themselves attract more enemies, but the individuals in those flocks are still safer than they would be all by themselves. Safety in numbers. But, in foraging, as in war, the ones who plunge into the fray first are also the most vulnerable. Guess who usually takes the hit?

“… we have witnessed that the only species in actively foraging mixed flocks that reliably get killed during hawk attacks are titmice (T. A. Contreras and K. E. Sieving, unpublished data), suggesting that the presence of flocks may be an important fitness cost to titmice.”

The high cost of leadership, I guess. I bet titmice don’t intend to lead at all, but when other birds see them on the move, they decide to tag along for the action.

As they say, “More research is called for.”

This discovery was yet another example to me of how there is a huge amount going on “out there” that is not immediately apparent—behaviors, sounds, meanings, patterns. A lot. It was humbling to find out–again–that something I stumbled across with amazement was already common knowledge among folks smarter about birds than me, which is a lot of people.

The wonder of our backyard–and yours–is that behind the veil of the obvious lies endless amounts of interrelated detail that makes up the bulk of what is actually going on, like birds listening in on each other for clues about food and danger, or mycorrhizal networks connecting myriads of plants and fungi into an “internet” of communication, or the unheard (to us) sounds of treehoppers drumming on stems to talk to each other. Endless. Infinitely connected.

They say that any part of infinity is also infinite. If so we’ve got enough infinity in the small yard outside our door to last many lifetimes.