Fall migration: some birds hit hazards and others find feeding bonanzas
By Barb Gorges
Mark and I were camping in the Cascades with our granddaughter and her parents, watching American dippers fly up and down the Sauk River when the unseasonably early snowstorm hit Cheyenne September 8-9.
The first rumor we heard about a bird migration catastrophe was from my sister and brother-in-law in Albuquerque who mentioned a lot of dead birds had been found in New Mexico after that same storm.
Albuquerque dropped from a record high of 96 degrees for the date to a record low of 40 with high winds. Up on Sandia Crest overlooking the city there was snow. Dead bird reports started coming in including 300 carcasses at White Sands Missile Range and more in other parts of the region.
Within a week, the major bird conservation organizations and the national media were writing about it. The best account is at the American Birding Association website, written by Jenna McCullough, a graduate student at the University of New Mexico, https://www.aba.org/the-data-behind-mysterious-bird-deaths-in-new-mexico/.
But there were also anecdotal reports of dead migratory birds in the west back in August, the possible culprit being the wildfires. Apparently, when smoke fills the air, the migratory birds leave, even if it is prematurely, so they may not have eaten enough to store enough fat for the journey.
Perhaps the birds can’t find the food they need along the way because the smoke is obscuring it. And breathing smoke weakens them. Mark and I had a taste of that on our drive back across Washington, Oregon, Idaho and Utah. Cheyenne had even thicker smoke Sept. 26 when it was engulfed in the orange plume from the Mullen fire.
Not all birds migrate. The non-migratory birds know their territory’s food sources well and are less likely to starve during rough times. However, many of the species that migrate are insect eaters, insectivores. They migrate south as far as Central and South America when it is too cold up north for insects.
There are birds that specialize in finding hibernating insects and their eggs in tree bark, like the brown creeper in winter in Cheyenne. But warblers and flycatchers want more lively insects, and swallows require flying insects.
No insects fly for a while after a freezing event. Even if the birds had stored fat for the journey, they would burn a lot trying to keep warm. Swallows are known to huddle together, and Jenna found crevices in the bank along the Rio Grande stuffed with emaciated, dead swallows.
What radar tells us
Weather radar stations around the country can pick up the movements of migratory birds. At Cornell Lab of Ornithology, the BirdCast team, https://birdcast.info/, besides forecasting migratory activity, processes the data to show the amount and direction of migration over time in active maps.
The night of September 8-9, you can see a hole in migratory activity centered on New Mexico, Colorado, and western Texas, Kansas and Nebraska—no bird movement. And none in much of Wyoming, but apparently no one reported high numbers of dead birds here.
Conversely, on Sept. 21 as I walked the dog along the Henderson ditch in the morning, the vegetation was alive with small birds busily hunting. I checked BirdCast and sure enough, overnight there had been a major migration push from eastern Montana down through Cheyenne and down all along the Colorado Front Range, as well as in the Pacific Northwest and along the East Coast. The night flyers had landed and were having breakfast.
One upside to the drought is the drawdown of reservoirs. When reservoirs are full, there are few migrating shorebirds stopping to feed. We went up to Bump Sullivan mid-September and it was a cornucopia: Mudflats full of feeding birds stretched a hundred yards between shore and water.
We saw sandpipers: Baird’s, least, pectoral, and spotted, and long-billed dowitchers plus great blue herons and sandhill cranes probing for invertebrates with their bills. On the water, hundreds of American white pelicans were feeding in long strings, shoulder to shoulder.
On Sept. 21 I also heard my first dark-eyed juncos in our neighborhood. While insectivorous birds abandon us for the winter, the seed-eating juncos join us. They aren’t quite ready to be bird feeder regulars yet—plenty of seed in the wild for now—but they haven’t forgotten how to find us. It would be interesting to do a banding study and find out which mountain ranges our juncos nest in.