Wednesday, September 23, 2020

Early Snowstorm Affects Swallows & Warblers

Tens of Wilson’s Warblers were among hundreds of Violet-green Swallows – a small proportion of the birds found after an early violent snowstorm.

Recent mysterious deaths of thousands of migrating swallows, warblers, and flycatchers in the Southwest, primarily in New Mexico, are now thought to be the result of the sudden and dramatic lack of food – small flying insects – caused by a historic early snowstorm, according to researchers at New Mexico State University. Initially there was speculation the fatalities were the result of smoke from western wildfires, but hundreds of birds collected after the recent storm showed the birds had no fat and extremely low weight, indicating they likely died from a combination of starvation and hypothermia.

During the second week of September, the Rocky Mountain states experienced an intense freezing storm that brought snow, near hurricane force winds, and unseasonable record-breaking cold temperatures. On September 8, it was sunny in Albuquerque with a record-high temperature of 96ºF. The next afternoon the severe snowstorm tore through the region with wind speeds over 70 mph and temperatures plummeting to historic lows.

The 55 to 60 degree temperature swing observed in New Mexico combined with hurricane force winds and wet snow very likely caused hypothermia in many birds, especially juveniles experiencing their first migration. Cold temperatures also affected the food supply for insectivorous birds as insects died or became dormant and were covered by snow. Certainly, insects were not flying through the air, as required by swallows and flycatchers. Migration is a dangerous period for all birds, as emphasized by the many bird deaths reported in five states, especially in New Mexico, during this unusually violent early snowstorm.

For a full account of the information used in this article, you can refer to the American Birding Association’s most recent Field Ornithology article authored by Jenna McCullough from New Mexico State University at https://www.aba.org/the-data-behind-mysterious-bird-deaths-in-new-mexico/