Abstract
I explored the avian nocturnal flight call phenomenon near Nogales, Arizona from mid-August through October 2015 and found a surprisingly heavy calling rate. My analysis of the 6-10 kHz audio frequency band revealed nearly 21,000 warbler and sparrow calls, 17,629 of which were loud enough to present well for classifying to a species category. Preliminary results suggest 82% involve 7 species of migratory sparrows, 12% are of undetermined species ID, and the rest from an assortment of warblers, other sparrow species, and Passerina buntings. Artificial light was minimal at the recording site and is not suspected to have significantly impacted the calling rate of individual birds or caused aggregation behavior. The high calling total may reflect channeling of night migrants in the lower atmosphere, perhaps due to concentration dynamics from regional montane terrain.