February 8, 2023
It’s hard to deny that Lewis’s woodpeckers are stunning birds. Seen in good light, their glossy green backs contrast with their pinkish bellies. An ashy gray collar separates the red-tinged head from the iridescent back. But the story of Lewis’s woodpeckers isn’t just a tale of a beautiful, relatively uncommon bird of the Rocky Mountains. There’s much more going on here than meets the eye.
It’s a sunny, late-winter day along the floodplain of western Montana’s Bitterroot River. The Lewis’s woodpeckers have been gone for months, but the story of their summer nesting remains. In front of us is a cottonwood snag, its top snapped off. From our vantage point, we can see a nest cavity that originally belonged to a northern flicker, a neatly rounded dark hole in the furrowed gray bark. A few feet above it there are several additional half-rotten cavities, designs engraved by decay in the cottonwood trunk. When we walk around to the other side of the snag, we can see another nest hole that has been excavated there.
Any of these cavities is a potential nest site for a Lewis’s woodpecker (Melanerpes lewis). And though it’s hard to imagine it right now, with the woodpeckers long-gone, this site is prime breeding habitat for these special birds.
Lewis’s woodpeckers along the Bitterroot River
Today I’m near Florence, Montana with Lewis’s woodpecker researchers Kate Stone and Mary Scofield. We’re on the MPG Ranch, a large and unique private property managed for conservation and wildlife habitat. The floodplain forest is a mature mixture of black cottonwoods (Populus balsamifera) and ponderosa pines (Pinus ponderosa). Old river oxbows bend across the flat, marked by strings of hawthorns (Crataegus) and willows (Salix). In the understory, snowberry (Symphoricarpos sp.) and mock-orange (Philadelphus lewisii) provide nesting cover for songbirds. The ground-layer vegetation is predominately reed canarygrass (Phalaris arundinacea) and leafy spurge (Euphorbia esula), both non-native species, punctuated by patches of native goldenrod (Solidago sp.).
Kate has been studying Lewis’s woodpeckers here since 2013. It’s an extremely thorough, multi-faceted project. During the breeding season, Kate and her technicians search their floodplain study areas for nest trees and monitor active nests. To track individual birds, they capture them and outfit them with colored leg bands and miniature radio transmitters. They’ve also studied Lewis’s woodpeckers in burned conifer forests, another common breeding habitat, and compared nesting success between these areas and the cottonwood groves.
Paying attention to the nest trees
Across this decade of study, Kate and her team have developed a much more detailed – and much more surprising – picture of Lewis’s woodpecker biology than a casual birder would ever be able to. Much of it centers around the nest trees – essential elements of summer breeding habitat for these birds.
“We have nine years of nest history for some of these trees,” Kate tells me.
On this winter day, with three months remaining before most of the Lewis’s woodpeckers begin to return, Kate and Mary are here to double-check some of their past data on nest trees. Lewis’s woodpeckers often nest in clusters, Kate tells me, with perhaps two to five nests in a particular patch of cottonwoods. This can make it difficult at times, looking at a digital map loaded with ten years of data, to determine whether a cluster of nest observations all came from the same exact tree. So today we’re walking through the floodplain to clear up some uncertainties, comparing field notes and photos of nest trees with what we see on the ground. For Kate and Mary, it’s one small part of the mountain of field work that makes up Lewis’s woodpecker research. For me, it’s a great introduction to the unexpectedly mysterious world of these birds.
Compared to the other woodpeckers that commonly nest here – northern flickers, red-naped sapsuckers, and downy woodpeckers – Lewis’s woodpeckers are rather unusual in their basic biology. They almost never excavate their own nest holes. Instead, they reuse those of other woodpeckers or make do with a partially rotten nook. Their foraging is different, too. Instead of hunting insects on tree trunks and plant stems like a downy woodpecker, snapping up ground-dwelling ants like a northern flicker, or lapping tree sap like a red-naped sapsucker, Lewis’s woodpeckers frequently hunt in midair. Like an oversized flycatcher, it’s common to see them flapping outwards from a snag to snatch wasps, beetles, or aerial ants.
We stop near a cluster of cottonwoods where Kate and Mary have some nest tree records to verify. Kate says that the nests tend to be high in the trees. In this floodplain forest they’re often in cottonwoods, but sometimes in a ponderosa pine. And especially if a tree is only half-dead, they can be incredibly hard to spot among the leaves. Sometimes, Kate tells me, the best way to find a Lewis’s woodpecker nest is to wait until the babies have hatched. Their insistent begging calls can give away the location of a previously invisible nest, as the parents work hard to bring insects to the fast-growing hatchlings.
Tracking Lewis’s woodpeckers
Typically, the same nest trees are occupied every year – but amazingly, the individual woodpeckers are often different. So far, Kate and her team have tagged 99 Lewis’s woodpeckers with radio transmitters. They’ve put colored leg bands on 141. While the leg bands allow them to recognize previously captured birds during the intensive, on-the-ground summer search for active nests, the transmitters give them important information about where these birds are moving when they’re out of sight.
Kate’s team participates in the Motus project, a global network of automated telemetry receivers managed collaboratively by a large partnership of wildlife researchers. What this means for Lewis’s woodpecker research is that, any time a bird passes within roughly 12 miles of a Motus receiver, Kate’s team gets a notification in real time of the bird’s location. This allows them to track arrivals, departures, and movements within the Bitterroot Valley – and to get a better idea of where Lewis’s woodpeckers go throughout the year.
And incredibly, using Motus receivers and lots of on-the-ground searching for birds with colored leg bands, Kate’s team is finding that only 15-20% of these woodpeckers return to the Bitterroot Valley from one year to the next. What’s more, only 2% nest again in the same tree. And of that 2%, only half of them pair with the same mate.
It’s a highly counterintuitive finding. Most nest trees are occupied by Lewis’s woodpeckers in succeeding years – but the individual birds are different.
“If you were a casual observer, you would assume it’s the same pair,” Kate says.
Following these radio-tagged birds away from the nesting area, the story gets even stranger. Where do they go? And what happens to the 80%, that vast majority that never return? Largely, we just don’t know yet. There have been a few Motus detections of Bitterroot Valley birds passing through southern Oregon. Kate suspects that the birds she’s studying may be among the Lewis’s woodpeckers that overwinter in northern California alongside their highly social relatives, the acorn woodpeckers. But there’s not yet good coverage of Motus receivers there, making it difficult to confirm this hunch – for now.
“It’s really surprising that we haven’t picked up more,” Kate says.
Generally speaking, Lewis’s woodpecker populations are in steep decline, for reasons that remain unclear. And with so many of the Bitterroot Valley birds just vanishing each year, it raises concerning questions about what is happening. Are they simply breeding in a different area the next year, where the Motus network is still too patchy to detect them? Or, in a much more concerning scenario, could all of the missing birds just be dying?
In an additional wrinkle, Kate mentions that it’s been extremely rare to find second-year Lewis’s woodpeckers in the Bitterroot Valley. Where are the two-year-olds? It’s another mystery. Could they be staying in California with the acorn woodpeckers, only moving on to breed once they turn three?
At a glance, it would appear that Lewis’s woodpeckers are thriving in the cottonwood forests along the Bitterroot River. There are some concerns for the future: many of the cottonwoods are aging, and few young ones are growing up to replace them. But for the moment, the breeding habitat here seems good. And indeed, the studies of nesting success that Kate and her team have conducted confirm that, for now, Lewis’s woodpeckers are nesting quite successfully in this area.
But the closer they’ve looked at these birds, the more puzzles have emerged. Where are the Bitterroot birds overwintering? What’s happening to the four out of five that never return? Where are the two-year-olds going? And in the midst of widespread declines, how can we take care of our populations of these beautiful woodpeckers?
Over time, more answers will likely emerge. And in the meanwhile, the next time you see a Lewis’s woodpecker, give it a closer look. As with so many of the animals around us, there’s much more going on than meets the eye.
Blake, W.M. & Stone, K.R. (2021, November 4). Fall 2021 Motus update. Retrieved from https://zivranch.s3.amazonaws.com/s3fs-public/2021-11-04_WMB_KRS_Update_Motus.pdf
Blake, W.M., Stone, K.R., Janousek, W.M., & Martin, T.E. (2022). Lewis’s woodpecker nest success and habitat selection in floodplain and burned forests in western Montana. Journal of Field Ornithology 0(0):1-15. Retrieved from https://zivranch.s3.amazonaws.com/s3fs-public/Blake%20et%20al%202022%20LEWO%20Paper.pdf
Stone, K.R. (2020, September 22). 2020 Lewis’s woodpecker research update. Retrieved from https://www.mpgranch.com/research/2020-lewiss-woodpecker-research-update
Vierling, K.T., Saab, V.A., & Tobalske, B.W. (2020). Lewis’s woodpecker (Melanerpes lewis), version 1.0. In Birds of the World (A.F. Poole, editor). Ithaca, NY: Cornell Lab of Ornithology. Retrieved from https://birdsoftheworld.org/bow/species/lewwoo