Bohemian Waxwings are having a moment. This winter, these far north breeders have ventured as far south as Santa Fe, New Mexico. Here in Colorado, Bohemian Waxwings have been relatively common in the Front Range this winter.
It’s been been a decade since Bohemians have been so numerous and conspicuous in Colorado. What’s brought them here? We’ve had deep snow and extreme cold in the Rocky Mountain west. While I don’t know if this has been the case farther north, where this species usually overwinters, one suspects that it is.
But perhaps it’s a fool’s errand explaining the Bohemian Waxwings southward movements. Cornell’s Birds of the World says this of the bird.
Notoriously irruptive, irregularly appearing in large numbers in regions south of normal wintering range. For example, only rarely reported from New Mexico, but in Apr 1959, huge numbers (about 10,000 individuals) arrived in Santa Fe and remained until early May (Ligon 1961). Late arrival at this southern locality suggests individuals moved into the area after depleting fruit supplies in more northern areas.
At least what we can say what the birds are doing here: devouring the berry-like drupes of Common Buckthorn, an invasive, non-native plant.
Just south of Denver, along the High Line Canal, a single Bohemian Waxwing amid 50-100 Cedar Waxwings quickly became a flock of 30-50 Bohemians among 100-150 Cedar Waxwings.
Today, January 15, that flock tripled in number. For the first time, I had the good fortune of standing amid a large, active, and noisy flock of Bohemians. They filled a small Buckthorn on the Canal’s edge. Dozens occasionally jammed in to my camera’s field of view.
While the photos of these gatherings aren’t particularly impressive, I like how much movement and activity they convey. Waxwings and a robin or too point in every direction. Some are in flight. Others are swallowing Buckthorn. Others are about to collect it. The birds only seem to do one thing in unison: throw themselves into flight, as a single, impressive flock.
When not eating, the Bohemian Waxwings trilled from high perches in the Canal cottonwoods. By comparison to the Cedar Waxwing’s call, the Bohemian’s call is slow and low. Between the robins, Bohemian Waxwings, and a few magpies, the Canal filled with a complex mix of sounds.
Waxwings and the Suburban Landscape
This year, many of the best places to see Bohemian Waxwings near Denver have been south and slightly east of the city, along the High Line Canal Trail. eBird shows that birders have reported Bohemian Waxwings throughout a 4 mile, as a car drives, and 7.5 mile, as the Canal winds, stretch of the trail from southeast Denver through Cherry Hills Village.
The Canal itself is a ditch dug by hand over a century ago. It used to carry water from S. Platte River, southwest of Denver, to the prairies north east of Aurora. Along it, a riparian corridor of cottonwoods, willows, chokecherry, Golden Currants and American plums developed.
These native plants provide important resources to the trail’s wildlife. Cottonwoods, willows, chokecherries, and plums are important host plants for moths and butterflies. These are themselves important food sources for birds during nesting season. Currants, chokecherries, and plums bloom early, providing insects and birds with nectar. The cottonwoods provide nesting habitat for native and introduced species, particularly Northern Flickers, Eastern Screech Owls, and European Starlings.
The chokecherries feed songbirds in autumn; they also serve as host plants for moths and some swallowtail butterflies. Meanwhile, the plums are both a critical host plant for moths and butterflies and an important late autumn food source for mammals, particularly coyotes.
The corridors has also proven a suitable home for weedy and invasive non-native trees and shrubs, particularly honeysuckles, Russian olives, Siberian Elms, and Buckthorn. These can spread voraciously. Tree of Heaven, European Spindle, Privets, the occasional lilac, and Golden Rain Trees, which are overused in landscape plantings, have also begun to move in.
So here in the southern suburbs of Denver and Aurora, our encounters with waxwings happen in a landscape altered by human activities. Meanwhile, waxwings and other birds continue to alter it, spreading seeds of Buckthorn across the canal and adjacent open spaces.
ISO Buckthorn
Birds ignore Common Buckthorn drupes until mid-to-late winter. It’s often the only fruit left standing at this time of year. So to find uncommon or rare birds, it often means being in search of the plant. In addition to the waxwings and robins, I’ve also seen White-throated Sparrows, Townsend’s Solitaires, Hermit Thrushes, White-crowned Sparrows, Song Sparrows, and Spotted Towhees feeding on or associating with Buckthorn.
All this leaves me with an ambivalence. Rarely do I seek out patches of invasive plants with any kind of joy or hope. But if I hope to find waxwings, I also implicitly hope to find these. And this stretch of the Canal is a wall of Buckthorn. Many of the adjacent yards also have patches of the plant, perhaps owing to the activities of robins and waxwings.
Not to be Ignored, Cedar Waxwings
While Bohemian Waxwing steal the show, Cedar Waxwings are also worth watching. They, too, acrobatically feed on Buckthorn, in Cirque du Soleil feats of balance and flexibility.
Cedar Waxwing on the High Line Canal, Cherry Hills Village, CO
Meanwhile, I’ve watched waxwings mellow out the laxative properties of Buckthorn by voraciously drinking. They’ll do this at puddles on pavement, as well as high in cottonwoods, where they gobble up melting snow.
An apparent pair of Cedar Waxwing used the snow to maintain their bond, exchanging it as a sort of gift. (Another Colorado birder reported similar behavior between Cedar Waxwings on January 7, and I saw it again on 1/15.)
This “passing behavior” is common during nesting season, when birds affirm their bonds through exchanges of food and water. According to Birds of the World, this behavior is not especially well documented in the winter among Cedar Waxwings: “The extent to which mates associate in winter and migratory flocks is not known.”
However, Bohemian Waxwings display this behavior, according to this 1978 article in Blue Jay, the long-running journal of Nature Saskatchewan. And according to the Birds of the World account of Cedar Waxwings, some pairs do indeed remain bonded beyond the nesting season.
For now, the birds remain committed to the Canal. Eventually, they’ll exhaust it as a food source and look elsewhere. They’re remarkably nomadic birds, after all.
Until then…
waxwing ripen
the winter
buckthorn
For more on the remarkable behavior of winter waxwings, see Mary Holland’s incredible post and photographs of a Bohemian Waxwing feeding on Bald-faced Hornet larvae.
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