Sunday afternoon in Borrego Springs, Merry and I walked into the library of the Anza-Borrego Desert Natural History Association on Palm Canyon Drive to hear a wildlife biologist talk about hawks.

That morning, we had watched two kettles lift off from the Borrego Valley — nearly fifty Swainson's Hawks circling on thermals, gaining altitude, and streaming north. We had gone out to the Borrego Springs Hawkwatch, a volunteer monitoring effort organized by the Anza-Borrego Natural History Association that has been counting migrating raptors every spring since 2003. The observation point is simple: a stretch of open ground with a clear view of the sky. The volunteers arrive early, before the sun heats the ground enough to generate the thermals the hawks depend on. They set up spotting scopes and wait. The birds are scattered in the landscape — perched on fence posts, on power poles, in the sparse trees along the washes. They are waiting too.

What happens next is one of the great spectacles of avian ecology, and it is driven entirely by physics.

As the sun heats the desert floor, columns of warm air begin to rise. The hawks feel it before any instrument could measure it — a subtle shift in the air, an invitation. One bird lifts off. Then another. They begin to circle, tightening their turns as they find the column's center, rising without flapping on wings designed for exactly this purpose. Swainson's Hawks have long, narrow wings relative to their body mass — a high aspect ratio that maximizes lift-to-drag in soaring flight. They are engineered by selection for the thermal column the way a sailboat is designed for wind.

As more birds commit to the air, the formation becomes a kettle — the birder's term for a circling group of raptors riding a thermal. From below, it looks like a slow vortex, birds spiraling upward in a widening gyre. They gain altitude — a thousand feet, two thousand — until the thermal weakens or they reach the altitude they need. Then, one by one, they peel off and stream northward on a glide, losing altitude gradually until they find the next thermal and the process repeats.

So when we walked into the ABDNHA library that afternoon for Lizzi Meisman's talk, the birds were already in our bodies. We had stood in the desert that morning and watched them rise.

We were a week into two weeks based in Borrego Springs, exploring Anza-Borrego Desert State Park and conducting a computational photography survey at the nearby Steele/Burnand Anza-Borrego Desert Research Center. The talk — part of the annual Borrego Springs Hawkwatch series — had caught our attention eye on a flyer that our friend Jean had forwarded to me. Lizzi is a wildlife biologist and NSF Graduate Research Fellow pursuing her master's degree under Matt Johnson in the Wildlife Department at Cal Poly Humboldt. Her subject was Swainson's Hawks in the Butte Valley — a high-elevation basin in Siskiyou County, California, where Brian Woodbridge began monitoring a nesting population in 1985. Lizzi had inherited one of the longest-running raptor study datasets in North America: forty years of nest occupancy and productivity records from a population of sixty-five to eighty breeding pairs in a landscape of juniper steppe and irrigated agriculture.

She was good. Enthusiastic, careful with her data, honest about what she didn't know. Her central research question was elegant: why do Swainson's Hawks sometimes select nesting territories that lead to reproductive failure? The ecological trap hypothesis — the idea that organisms can key on environmental cues that no longer correlate with actual fitness outcomes — is one of the most important concepts in conservation biology, and Lizzi was testing it in a system with rare temporal depth. In the Butte Valley, crop rotations and water availability shift the foraging value of a territory year to year, but hawks may be selecting nest sites based on structural features — the tree, the openness of the surrounding landscape — that remain stable while the food base changes beneath them.

The multivariate statistics were returning weak connections, and she was candid about it. During the question period, I asked whether she was tracking individual birds to build daily activity budgets. She wasn't — the resources weren't there. I asked about the prey base. Not tracked. I asked about site-specific climate data — temperature, precipitation, soil moisture records that could be overlaid against four decades of nest success. She had none. The long-term dataset was a treasure, but it was a treasure without context. The signal was hiding in what wasn't being measured.

After the talk, I introduced myself and told her about an open-source climate analysis tool I've been building that could pull forty years of historical weather data for the Butte Valley from reanalysis archives. She was interested. We exchanged emails. I sent her a note the next day offering to build a demonstration.

That's how conservation biology works, sometimes. You go to a lecture because it's a Saturday and you're curious, and you end up offering a small piece of infrastructure that might help a young scientist find the signal she's missing. One field ecologist reaching across a generation to another.

Font's Point

On Monday, our friend Frank Padilla drove Merry and me out to Font's Point — the great overlook into the Borrego Badlands that I wrote about in my memorial for Paul Ehrlich. As we stood on the rim, staring into four million years of exposed sediment, Swainson's Hawks circled on thermals above us. After the morning kettle and Lizzi's lecture the day before, I was seeing the hawks differently — not just raptors riding thermals, but migrants in passage, part of the formally monitored northward movement through the Borrego Valley, circling above me on the same day I learned we had lost one of the scientists who spent his life arguing that such things mattered.

Swainson's Hawks make one of the longest migrations of any raptor on Earth. Breeding populations from western North America — the birds Lizzi studies in the Butte Valley, the birds I was watching at Font's Point — winter on the Argentine pampas, roughly fourteen thousand miles round trip. They travel in flocks, sometimes numbering in the thousands, riding thermal columns to gain altitude and then gliding on a heading until the lift gives out and they need the next thermal. The migration follows the Central American land bridge, funneling birds through narrow corridors where the spectacle becomes visible to anyone who knows to look. Last year in Borrego Springs, Dr. Pete Bloom attached a GPS backpack to a young hawk they named Betsy. Betsy has since completed a migration loop, and as of this week is heading north once again along the west coast of Mexico and is expected to arrive soon.

The Borrego Valley is one of the staging areas on the northbound leg. Desert thermals are strong, predictable, and early — the same heat that is making this March anomalous for humans is, for the hawks, a reliable engine. They need the warm air to rise. The heat dome that had been building over the Southwest all week — pushing temperatures above ninety in a season that should still be in the seventies — was also the thing lifting these birds skyward. There is an uncomfortable elegance in that: the same atmospheric anomaly that signals a changing climate provides the energy the migrants need to complete a journey shaped by millennia of stable seasons.

Tuesday Morning

This morning, Merry pulled me away from my coffee and my inbox to drive out to the morning hawk watch again. We arrived twenty minutes too late. The kettle had already formed and dispersed. We saw Turkey Vultures riding the thermals, a Cooper's Hawk, Ravens in flight — but the Swainson's Hawks had already committed to the air and gone north.

That's field biology. The birds don't consult your schedule.

The Longer View

I have been thinking all week about what it means to watch — and about the limits of watching.

The Borrego Springs Hawkwatch has been counting Swainson's Hawks every spring since 2003. Twenty-three years of season totals, recorded by volunteers standing in the desert with spotting scopes. The data show enormous year-to-year variability: season totals of over sixteen thousand in 2023, nearly twelve thousand in 2017, but barely a thousand in 2019. This year, with the season only half over, the count is tracking in the low one-thousand once again — and potentially the lowest in the history of the watch.

Nobody knows why. The heat dome is one hypothesis: stronger thermals could be lifting the birds higher and faster, carrying them above the observers' detection ceiling, or the anomalous heat could be pushing the corridor eastward toward the Chocolate Mountains or the Imperial Valley. The timing may have shifted. The population itself may be declining. A single observation point on the ground, with a fixed aperture and a limited season window, can tell you what passes through — but it cannot tell you what didn't come, or where it went instead. The variability in the dataset is itself a signal, but it's a signal that resists easy interpretation.

Lizzi Meisman inherited a forty-year dataset from Brian Woodbridge and is trying to understand why hawks choose the wrong territories. The Anza-Borrego Natural History Association organizes volunteers to count migrants every spring. Merry pulls me away from my computer to stand in the desert and look up. All of these are acts of attention — patient, sustained, often unglamorous attention — directed at a species that has no idea it is being observed and would not care if it did.

The Swainson's Hawk doesn't know about ecological traps. It doesn't know that the alfalfa field it chose last year has been converted to a crop with a different mowing schedule that no longer flushes the grasshoppers and voles it needs to feed its nestlings. It doesn't know that its fourteen-thousand-mile migration depends on atmospheric physics that are shifting under the pressure of a warming climate.

What the hawk knows is the thermal. It knows when the air is right. It commits to the column with its whole body, and it rises.

I spent Saturday morning watching two kettles rise from the desert floor, and Sunday afternoon in a library learning about the science of these birds from a young researcher who has given her career to them. I spent Monday watching them circle over four million years of exposed sediment at Font's Point. I spent Monday morning arriving twenty minutes too late, seeing only the empty sky where they had been. Four encounters with the same species across three days, each revealing a different layer: the spectacle, the science, the deep time, and the absence that reminds you the birds owe you nothing.

This is what long-term ecological monitoring does. It makes visible the patterns that would otherwise remain hidden — the slow decline in nest success, the shifting relationship between habitat and fitness, the multi-decade signal of climate change working through a food web. Woodbridge started counting in 1985. Lizzi is counting now. The volunteers in the Borrego Valley are counting this morning. None of them can see the full pattern from where they stand. But each count, each season, each year of data is a point on a curve that only becomes legible across decades.

The hawks are rising over the Borrego Valley. The air is warm and getting warmer. Somewhere to the north, the Butte Valley is waiting — juniper steppe and irrigated fields, nest trees that have been occupied for forty years, and a young scientist trying to understand why some of them fail. The thermal column connects them all: the winter range, the migration corridor, the breeding grounds, the science, the watching.

I'm going back out with Merry this evening to see where the hawks come down — or tomorrow morning, earlier this time, to try again for the kettle. The season is nearly over. There will be more hawks, for now, if you know when and where to look.