Far from the reach of the destructive flames of catastrophic wildfires in California and the Pacific Northwest, but not beyond the pervasive billows of smoke from the conflagrations, something weird and disturbing is happening here in the southern Rocky Mountains.

Thousands, if not millions, of migrating birds are dropping dead for no obvious reason.

Where I live in northern New Mexico, incidents of mass bird death are being reported widely among communities, on social media and in local news reports.

On Sunday I was working outside of the town of Taos, pulling up prickly tumbleweed on my high desert property. Beneath one of the plants I plucked from the sandy earth was a single, brilliant yellow western tanager. It appeared to have crawled under the small bush, hunkered down and died sometime recently. There was no sign of trauma or decay, just a small but beautiful dead bird.

Weird, but not nearly as strange as the scene that journalist Austin Fisher came across just about twenty miles further down the Rio Grande river from my home. There he came across a cluster of dead birds near the village of Velarde and posted video of the scene on Twitter.

The bulk of the reports seem to be coming from New Mexico, but the bird deaths are also now being reported throughout the southwest in Arizona and Texas. It also seems to be limited to migratory birds. Species that tend to stay put in the southwest rather than heading towards Mexico and further south in the winter appear unaffected.

Scientists are just beginning to get a handle on the situation and gather data. Wildlife spotting app iNaturalist is encouraging the public to photograph and document dead birds in the area to help wildlife biologists understand the extent of the die-off.

While it may be too soon to understand what’s really going on, Andrew Farnsworth and Benjamin Van Doren from the Cornell Lab of Ornithology point to particulate matter from wildfire smoke in the air as a potential culprit.

“Migrating birds encountering high concentrations of toxic compounds from or particulate matter like smoke at altitudes well above ground level could be at serious risk,” they write. “It is also unclear whether aerial insectivores are overrepresented among the dead species, but it may be that birds actively foraging for aerial food items like flying insects are at greater risk—either from direct smoke inhalation or lack of food if their prey are influenced adversely by smoke or its correlates.”

The region has also been subject to a bout of weird weather extremes recently. Last week saw a wild swing from hot weather approaching triple-digit highs at lower elevations to a freak summer snowstorm within about 24 hours.

Farnsworth and Van Doren point to extreme heat throughout August as another potentially lethal factor. They encourage bird watchers to use the iNaturalist app or report bird casualties to a local US Fish and Wildlife Service Office.