A Ruby-crowned Kinglet (Regulus calendula), a less gregarious winter migrant to the hill. They are often found in mixed-species flocks but are outnumbered, at least 10-1, by Golden-crowned Kinglets. (Image: Brendan McGarry)

Everywhere I looked there were birds. Sprites in perpetual motion, determined to find their next meal. Kinglets, chickadees, creepers, nuthatches, and wrens worked through the forest understory as I sat watching. It hardly felt like they noticed me. If I kept still enough, I’d just melt into the background, or at least that’s how it feels when you encounter a winter feeding flock.

Back in October I started noticing mixed-species flocks of chickadees, Golden-crowned Kinglets, and a few Pacific Wrens around my yard. This is my personal cue for the changing of the seasons. When the last of the year’s fledglings are self-sufficient, the winter migrants have arrived, and breeding territories are moot, it’s officially winter. The majority of birds are now much more concerned with surviving the cold, less abundant months, than defending their corners of the forest or your backyard.

Call them mixed-species foraging flocks or winter feeding flocks, every year these groups of birds form during the non-breeding season on Capitol Hill and across our region. They move together, across the landscape, foraging as they go, all day long.

The birds that make up these flocks in our part of the world have a fair amount in common. They are all small, active birds that eat a lot of insects (but also seeds and fruit). Most of them glean their meals from tree bark crevices and the undersides of leaves. Some are faster moving and more balletic, like kinglets, twirling about foliage and eating unseen tiny morsels. And others feel more methodical, like Brown Creepers, who do as they are named and crawl up and down tree trunks in search of sustenance. But they all seem to see the value of keeping close together while foraging this time of year.

Across the animal kingdom, it’s not unusual for animals to gel together over food or other resources. Think of the elephants, zebras, and gazelles around the watering hole in Africa or gulls and cormorants about a bait ball on the Salish Sea. However, forming a mobile, living flock that moves together instead of focusing on a static resource is a different thing altogether. Various bird species across the globe engage in this behavior, from tropical forests in India to the Boreal forests of North America, but only a specific handful, and depending on the place, only at certain times of the year.

In a world represented (often erroneously or simplistically) as bloody and ruthless by biological research over the past 200 years, you might wonder why birds of different species, similar size, and nearly the same food preference would choose to fly around together. Wouldn’t that just make things harder, more competitive? Isn’t winter a hard time of year?

Townsend’s Warblers (Setophaga townsendi) are a welcome bit of bright color in a mixed-species flock. (Image: Brendan McGarry)

Indeed, it’s hard work keeping tiny birds alive in cold conditions. Small songbirds have insane metabolisms and have very little room to carry around extra bulk. Golden-crowned Kinglets spend almost all day eating as much as they possibly can – the equivalent of our eating around 27 large pizzas from the moment we wake to right before bed, while continuously walking and running between meals. Kinglets are little caloric marathon machines and the phrase “eating like a bird” was clearly coined by people with no real knowledge of birds. Kinglets naturally flock up during the winter and you can hear them picking through a forest canopy regardless of the other bird species around – they are often the only birds I see in our mountains during the winter. But in places a little less harsh, they are frequent members of these mixed-species parades.

Those researchers who have attempted to pin down the particulars aren’t willing to state absolutes about how and why this works, but they generally agree that these groupings are a net benefit to the birds who participate. (Why would they all do it after all?) Some members of the flock might find better foraging within a group of many eyes. Others might take a bit of a hit in terms of the calories because they have to share, but don’t have to worry about getting snuck up on by predators (I have regularly found owls because of the scolding calls of these flocks). And yet others seem to gain across the board because they can forage in places they’d normally avoid on their own, because it puts them at risk. (I also like to think they might just like the company, but science has a hard time proving such statements.)

What’s clear in all these feeding flocks, no matter the place or conditions, is that different species play different roles. Studies focusing on these groups call the birds that have a higher influence on where the flock goes “nuclear” species. They are typically birds that are generalists, glean their food (as in picking it off of surfaces), and have a high level of intraspecific sociality (they spend time interacting with each other). Enter the chickadees. Both our Black-capped and Chestnut-backed Chickadees are often at the center of a mixed-species flock, even if it would take much keen observation to see their influence on the group as a whole. It’s almost as if the fun, gregarious chickadees make everyone want to join in, but their vigilance towards predators, loud vocal communication, and propensity for traveling in close family groups during the winter are better explanations of this role.

A Black-capped Chickadee (Poecile atricapillus) inspecting a willow bud for small insects. (Image: Brendan McGarry)

Other birds also follow along, though they don’t seem to have as large of an influence on things. Call them associate or attendant species, they trail along after the flock finds them, often in more static territories. Wrens are good examples of this because they aren’t migrants and often stay within a general homeground year-round. A Bewick’s Wren like to glean and pick through the forest but they are much less interested in close nit flocks. However, if a flock moves through, offering them the chance to find different resources all while making it safer to do so, a wren will indeed join.

Mixed with the chickadees might be Red-breasted Nuthatches, Golden-crowned and Ruby-crowned Kinglets, Downy Woodpeckers, Pacific Wrens, and even the odd Townsend’s Warbler who didn’t escape to Mexico for winter. I have few adjectives for these flocks other than magical. Finding yourself surrounded by a group of birds that are suddenly offering obliging closeness feels otherworldly, like we’d suddenly shrugged off the chains of being marked as predators. Even if the reason these flocks are seemingly oblivious is that they are so hungry they take calculated risks in our presence, an encounter still is nothing short of captivating.

If you have a moment for a winter walk, try to track down a winter feeding flock. Learning to listen for birds like Golden-crowned Kinglets and Brown Creepers, whose high, bright voices are easier to pick out from afar (or use the Merlin App to listen), is a good bet. Depending on the weather and the forest, they might be moving far overhead in the trees or be pushed by rain or cold into the understory. You might not find them cruising through Broadway street trees, but a lightly forested side street, Interlaken Park, or the Arboretum are good places to seek them out. If you are so lucky to find these flocks – take a moment and look and listen.

You’ll see kinglets hovering at branch tips, chickadees hanging upside down, creepers scaling tree trunks, and maybe even the sudden flash of color as a Townsend’s Warbler flits into view. No matter who is in attendance, I can promise you it will feel like an encounter with fanciful fairies, rather than a roving eating machine. To me, it feels particularly in tune with the winter season, reminding me to stay grounded in the present rather than wishing for warmer, brighter days.

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