It’s been described as among the “dullest, most drab” birds in North America. It’s not widespread, and the places where it lives are remote, far from most research institutions and most researchers. It’s perhaps not surprising that the gray vireo – a small desert songbird – has been almost entirely overlooked by scientists.
But Dr. Silas Fischer has helped correct that. Across seven summers, Fischer studied gray vireos, tracking their nesting, fledging and migration. Eventually, Fischer was joined by fellow biologist Dr. Gunnar Kramer, who expanded the research to other species.
The scientists found that these often-overlooked desert birds have powerful stories to tell – about how our fellow creatures may adapt to climate change, and about the limits of that adaptation.
“We hope our models are wrong,” Fischer said. “We don't usually say that as scientists. But in this case, it's really true.”
Amidst historic drought and heat, West Texans might imagine they’re bearing the brunt of climate change. They’re right. Our region is a climate hotspot, and creatures here – especially birds – are paying the price. Desert bird communities have collapsed in recent decades.
For insight into those declines, Fischer turned to gray vireos. The birds are less than 6 inches long, weigh half an ounce and, as their name suggests, are mostly gray. They nest in junipers in the foothills of sky-island mountains, including, in West Texas, the Chisos and Guadalupes. Fischer did their research at the Sevilleta National Wildlife Refuge, near Socorro, New Mexico.
In assessing reproductive success, scientists usually consider how many young birds survive long enough to leave the nest, or “fledge.” But by placing radio transmitters on young birds, Fischer tracked post-fledging survival. They found that survival plummeted under very specific conditions.
“And so we found that the drought index,” Fischer said, “basically the cumulative drought index over 18 months leading up to the breeding season, was the most predictive of fledgling survival.”
Like many desert creatures, gray vireos get all their water from what they eat, which in the case of young birds is insects. Extended drought means fewer insects in summer. With a diminished insect supply, young vireos are hard-pressed to survive their first vulnerable days out of the nest.
By measuring drought impacts, and studying climate models, Fischer concluded that gray vireos are almost certain to vanish from Sevilleta by 2050. Whether the birds might shift their range northward, or whether the entire species is doomed, is uncertain.
“It just really hit home once I actually saw the plots of what drought would look like relative to the historic baseline,” Fischer said, “and it's chilling.”
To track migration, Fischer and Kramer placed tiny geolocators on gray vireos, along with other desert songbirds – ash-throated flycatchers and Scott’s orioles. The orioles and flycatchers wintered in central and eastern Mexico, they learned. Vireos journeyed to Baja California, before returning to New Mexico to nest again in the same cluster of junipers.
To simulate climate-change impacts, Kramer heated the nests of desert wrens and flycatchers. The nestlings were small, but they rebounded and survived as well as birds from unheated nests. It suggests some desert songbirds may be better equipped for a warming world, Kramer said.
“In the case of wrens and flycatchers, I think we actually left feeling a little bit more hopeful for them being able to survive in the future at Sevilleta,” Kramer said. “But that's very different from what the vireos experienced. It's just complicated.”
Desert birds are hardy, but they have their limits. And some could vanish from our region, or even our planet, before science has taken their full measure.
This story was made possible by generous donations from supporters like you. Please consider showing your support with a contribution today.
