Category: Field Observations

The thrill of discovering “new” birds in the footsteps of Denver’s first ornithologist

What the century-old reports of Denver’s first ornithologists tells us about the birds and changing urban landscape.

In 2015, I became a “patch birder,” focusing my outings near my central Denver apartment. Usually, this meant visiting Cheesman Park and Denver Botanic Gardens next door. In part, I did this to spend less time in my car and more time in the field. But I also did so because at that time, Cheesman and the Gardens were “underbirded,” a term meant to describe locations with relatively few checklists on eBird.

At the start of 2015, fewer than 90 species had been reported to eBird from the two locations. This gave me the opportunity for one of the undisputed thrills of birding: To “discover” species in the middle of an urban center where many had yet to be recorded — in this case, central Denver.

So that spring, I visited both locations regularly — and I was rewarded with “discovery” after discovery. In April and May alone, I added 16 species to the joint Gardens/Cheesman hotspot list on eBird. In fall and winter, I added another 11. With fresh attention to this rather overlooked location, more other birders joined in. By the end of 2015, the hotspot list had grown by one-third, to more than 120 birds. In the years since, birders have boosted the eBird checklist to 150 species.

Among these additions were many “good” birds for urban Denver: Red Crossbill, Common Poorwill, Brown Thrasher and Sage Thrasher. Philadelphia Vireo, a rarity, visited in September 2015, giving good looks to me and Chris Rurik, who identified it. In May 2017, another local birder found Virginia’s and Black-throated Gray warblers, and in April 2018, both Long-eared Owl and Loggerhead Shrike on the same day! Suddenly, a tepid, back-burner destination on Denver’s eBird map was hot.

I learned a couple of valuable lessons birding Cheesman and the Gardens in 2015: eBird is an imperfect guide to the reality of birds in our region, and there is a long history of birding in Colorado still awaiting discovery.

So many of us rely on eBird to lead us to lifers, rarities and “good” birds — and yet, here in central Denver, hidden from eBirders for years, were at least 150 common, uncommon, and rare species.

Digging into the history can help us understand how our present-day finds are often encounters with birds that have long visited our state and its people . . . people like William H. Bergtold, whose century-old footsteps I would soon find myself retracing in Cheesman Park.

Born in 1865, Bergtold lived and birded in central Denver more than a century ago. He came to Colorado, as I had, from the Northeast; we both grew up in upstate New York. For a time, he even worked for my current employer, the University of Denver, teaching in DU’s medical school at the end of the 19th century.

An 1899 note in the journal Science reported that Bergtold was the first president of what may have been the first bird-related organization in the state, the Colorado Ornithological Association. Over the first three decades of the 20th century, he published numerous reports, articles, and books on Colorado’s birds. Those writings led me to Bergtold. Yes, while looking for Cheesman’s birds, I found one of the park’s first birders.

Bergtold wrote one of the state’s first books for birding, A Guide to Colorado’s Birds. Through his articles, he did something further — he told stories of the times. In a 1921 article about the “English Sparrow” (now House Sparrow) and the rise of motor vehicles, Bergtold speculated that the transition to automobiles from horses in urban centers might reduce the population of a despised non-native bird. Not only would fewer horses mean fewer horse droppings (road apples?!) for starving sparrows to comb for morsels, it would “probably also (make) the species’ street life so hazardous and fatal as to drive it largely out of the business area” of downtown Denver.

Many of Bergtold’s reports focused on birds in Denver and surrounding cities. He publicized other birders’ accounts of uncommon and rare birds. Noteworthy was a pair of Northern Cardinals that apparently nested in Littleton for several years. Reading Bergtold’s reports today, I can’t help but marvel at the city of a century ago — its natural and human-made landscapes, the birds that populated them, and the people who watched those birds.

 “The Birds of Denver: An Annotated List,” Bergtold’s 1917 essay in The Wilson Bulletin, is riveting for what it tells us about bird diversity in Cheesman Park and around the city. Some species we take for granted today were far less numerous in Bergtold’s time — and others that were common here in his day are scarcer now.

Writing about the American Crow, Bergtold noticed one “flying over Eleventh Avenue and Corona Street, December 7, 1913.” Another Crow was “seen in Cheesman Park, May 1, 1917.” Where he once noticed a single bird, I have watched hundreds of crows fill the park, which seems to be a staging ground for overnight roosting in late autumn and winter. Spotted Towhee, a rather ubiquitous backyard sparrow these days, was even scarcer. On Jan. 1, 1913, Bergtold wrote, “One detected in Montclair,” a Denver neighborhood 3 miles east of Cheesman. Black-capped Chickadees (in those days called Long-tailed Chickadees) hadn’t even begun nesting in Denver but instead were “regular winter visitors,” he said.

His reports also reflect what the city has lost to human alteration of once-natural landscapes. Pine Siskin was once a common spring nester in Denver, the bulk arriving “early in March, and many linger till June . . . probably going to higher altitudes to nest a second time.” Bergtold tells us Black-headed Grosbeak and Bullock’s Oriole were common breeders throughout the city a century ago. Although less common, Lazuli Bunting and Northern Mockingbird both were regular summer breeders in the city, too. Although Colorado Breeding Bird Atlas II lists them all as breeders in Denver County, none seems as common in the city as Bergtold suggests they once were.

One bird I’m particularly fond of roosts in the midst of these losses and gains. According to Bergtold, Common Poorwill was an infrequent migrant through Cheesman Park — and it still is today.

Having stalked through Cheesman a century after Bergtold, I like to think there was a connection between the poorwills we both encountered. I imagine that through decades and generations of humans and birds — then, now, and after us — the poorwills come and go, only occasionally resting in places like Cheesman where birders decide to look.

To read more about Bergtold, consider these articles:

This essay first appeared in the October 2022 newsletter of Denver Field Ornithologists, The Lark Bunting.

Featured photo of Cheesman Park in Denver by flickr user Ken Lund.

The Nighthawk’s Trajectory

What the trajectory of Common Nighthawks tells us about the suburban landscape.

I’m an agnostic in all things but nighthawks, for with the bullbat I hold this belief: one cannot pursue the bird directly; rather, one can only seek a trajectory that may someday cross theirs. 

My faith in the bird was born amid their southward migration through Denver, Colorado, in September 2015. I’d gone looking for nighthawks in a place where and at a time when I thought it likely I might see one. Common Nighthawks are (mostly) crepuscular; they hunt for flying insects through dawn and dusk. Walking around central Denver’s Cheesman Park after sunset, eyes aimed upward, I found only brown bats. I sat a while, awaiting night, and watched these other things with wings. Then, I left.

In truth, I just readied to leave. I sat in my car and, though it was a Sunday and though it was evening, I compulsively checked my email. A (lengthy) message from my department chair at the University of Denver greeted me. Compulsively, I read it, though I believe one should neither mix time off with work nor birds with the same. Dusk gave way to night. The bats gave way to a still park.

At the end of the email, nighthawks. 

A trio, emerging from the nearby neighborhood, furiously pursued insects under the park’s streetlights. I left my car and followed them. Nighthawks, like swallows, feed on the wing, catching insects as they fly. They are strong, agile fliers. I have seen them cut upward, leaning backward as they do, in pursuit of prey. They make micro-adjustments that give them a “tipsy” appearance, as Pete Dunne puts it in his Field Guide Companion. To me, they appear confident in the air. Untouchable, even. Nighthawks always seem to be beyond their human-observer, even when approaching them—a twist of angles always cutting away. Unlike songbirds, which rarely fly directly at people, this trio chased their prey wherever it went, even if it meant flying directly at me. 

An arm’s length away, a nighthawk.  

Photo credit: "Nighthawk at Dusk (Centennial, Colorado)" by Jared Del Rosso
Nighthawk at Dusk (Jared Del Rosso)

One can only seek a trajectory that may someday cross the trajectory of a nighthawk. I spent this past summer seeking just that. I let my dogs lead me. I indulged every detour and delay. We turned home when they wanted to. We inspected dead ends. We doubled back on trails. We lingered when the dogs wanted to linger. We sat together in fields and on curbs. I suppressed my better judgement of where and when the birds would appear. By maintaining the appearance of not seeking nighthawks, I hoped I could fool serendipity into delivering them.

I did so to try to document the bird’s presence in Centennial, a southern suburb of Denver, during the bird’s nesting season. A mid-June sighting gave me hope. My dogs and I sought the birds above a buggy marsh at a local open space. The setting sun inspired the complex chorus of catbirds, blackbirds, and sparrows. But I missed a simpler sound: the buzz of the bird I sought, the distinct, nasal “peent” of a nighthawk. As dusk deepened, my dogs decided it was time to head back to our car. (One dog is afraid of the dark and what it means in Colorado: wild canids. The other is simply not much for walking.) I obliged, though I wanted to keep seeking. 

Nearer to the car, the dogs changed their minds, insisting I let them chase each other around me. Though leashed, the dogs sprinted circles. To keep myself from their tangle, I spun with them. Once, twice, then—and only because the dogs had chosen when to turn back and when to stop for play and when to turn me in the right direction—a nighthawk. 

I seek the nighthawk’s trajectory because I measure the world by this bird. They arrive in Colorado late in spring migration, just as that season tips toward summer. They leave before autumn begins whispering of winter. But the bird isn’t just a sign of the seasons. Their presence speaks of the complexity of our climate, the non-human world, and the human/non-human nexus. Obligate feeders on flying insects, the Common Nighthawk’s steep population decline over the past half-century may relate to broader declines in their prey, owing to pesticide use, the warming planet, and other factors. Nighthawks are losing habitat, too. Some of that habitat is their wild habitat of grasslands and forests. But they’re also losing built habitats in urban and suburban environments. Nighthawks use the flat, gravel-covered roofs of many urban buildings as nesting sites. Unfortunately for the birds, most new development forgoes gravel for other materials, such as rubber. (Patches of gravel, installed on flat roofs, are a potential compromise that may support nesting nighthawks. New Hampshire’s “Project Nighthawk” is experimenting with this.)  

The fate of Common Nighthawks is tethered to us, in ways that the fates of many non-human animals are. But it isn’t easy to observe our entangled destinies. Nighthawks are not like the chickadees that visit our feeders, the finches and phoebes that nest on nooks around our houses, the corvids that seem more at home around our homes than we do, or the hawks that hunt on our highways. Nighthawks nest on our skylines. They migrate at incredible heights, and the vast majority of these birds pass over our summer and fall activities without being noticed. By day, they disappear into trees, grasses, and rocks. Their cryptic feathering renders them invisible. If you’ve ever lucked into a sighting of a nighthawk on a tree, you know how easy it would be to overlook the bird. You also know that nighthawks don’t care that you’ve found them. Their faith in their camouflage, their use of difficult to access perches, and the fact that they have no need for daytime activity allows them to tolerate proximity to us. 

Photo credit: "Perched Common Nighthawk (St. Paul, Minnesota)" by Jared Del Rosso
Perched Nighthawk along the Mississippi River (Jared Del Rosso)

Ultimately, my trajectory and the Common Nighthawk’s did not intersect during their nesting season. Perhaps this is a sign of the species’ decline or of my neighborhood’s hostility, with our grassy lawns and dependence on pesticides, to the birds and their prey. Perhaps it is only that I have not yet found our shared trajectory. 

But I have learned something else from this effort. Pursue this uncommon bird, during the uncommon hours of dawn and dusk, and you will find the trajectory of other uncommon creatures. Those brown bats, one of which dropped me to my knees by hunting at the brim of my hat. A raccoon, ambling down a drainage ditch. A coyote, patrolling an undeveloped field. Fox kits, playfully hunting along a neighborhood path. Great Horned Owls, perched in suburban parking lots and cemeteries. A Mule Deer pair, cautiously watching the human animals who ride bikes, and toss baseballs, and walk dogs while seeking nighthawks in fields near riparian corridors.

This essay originally appeared on the Center for Humans & Nature’s blog.

Featured image by Kenneth Cole Schneider @ https://flic.kr/p/2j6PJNM

From the Field #2: More Nighthawks, More Flying Ants

Last night, I arrived home from some errands around 6:30 PM to find a flock of Common Nighthawks feeding over my neighborhood in the southern suburbs of Denver. Two or three of the birds became several became a dozen then two then more still.

The birds flew wide laps around my neighborhood, occasionally streaming over my house. They were silent the entire time, as they fed on flying insects. The most likely prey were more flying ants. As I walked through my yard, I saw small insects taking flight. They stood out because they were not visiting, as the bees and flies and wasps and beetles do — my wildflowers. Rather, they seemed to float upward as they went.

I pursued a few of the insects, but most beat me to the sky. Finally, on a dog walk a bit later in the evening, I hawked one from its flight. (In truth, I cupped my hand in its path, causing it to land on my palm.) It was, indeed, a small flying ant.

The nighthawks looked dramatic in the late light of summer. Our western sun, as it dips toward the Rocky Mountains, is particularly strong and bright. The sun lit the nighthawks. Their white markings — their throats and underwings — shined.

The birds cast shadows on themselves, their long wings darkening their chests and flanks. This added to the drama of their flight, as they cut upward, backward, away, then back toward me.

I hope I never tire of this simple thrill — to be in the presence of these birds, who I barely understand. They seem to come out of nowhere. Not unlike the flying ants they pursue, which leave the rain-softened soil in late summer, nighthawks spend their days unseen. And where? Building tops? Perched on the cottonwoods lining the trails in Denver?

And then all at once, they arrive. Then all at once, they don’t.

In the Field #1: Common Nighthawks

On Friday night (August 12), a group of four or five Common Nighthawks (Chordeiles minor) joined a few swallows in feeding over my home and neighborhood. It’s always something when this happens — the birds flying relatively low, low enough to get good views (but not low enough for good photos).

The visit likely wasn’t a coincidence. Soon after the birds left, I spotted a few flying insects in my yard. They seem to be one of the nighthawks favored late-summer prey, flying ants, though I’m still working to confirm my tentative i.d.

According to the wonderful resource, Birds of the World (subscription required), a 1940 study of the stomach contents of 87 Nighthawks found that flying ants constituted about 25% of the mass of what the birds ate. Flying ants apparently emerge in late summer and, so, are a critical food source for migrating Nighthawks, not unlike late blooms (and feeders full of sugar water) are for migrating hummingbirds.

We’re in the early days of the Common Nighthawks’ southward migration. In past years, I’ve seen them in great numbers (for a suburban environment) in my neighborhood, encountering flocks of a dozen or two or three feeding over area parks. Here’s hoping this year brings the same.

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