Both findings could be correlated with climate change, although more investigation is needed to confirm. This study presents a new counting method that could prove useful for studying other soaring raptor species, especially at topographical "bottlenecks" like large water crossings.

Turkey vultures are facultative migrants, meaning some individuals migrate and some do not. The western North American breeding population typically migrates south in the winter, with some individuals journeying as far as Venezuela. Being relatively big-bodied, vultures utilize thermals and updrafts to travel efficiently, which funnels their movements along ridges and other landscape features that result in suitable air phenomena.

At some junctures, however, they must traverse large bodies of water. At Rocky Point Bird Observatory, located on a military base on the southern tip of Vancouver Island, Canada, researchers recorded daily estimated totals, or DETs, of vultures for 25 years as the birds congregated before crossing the 18-kilometer-wide Strait of Juan de Fuca.

To obtain these DETs, the team paid close attention to what are called "kettles"—groups of vultures spiraling upward inside a thermal, so named from a kettle-shaped land formation at one of the first established hawk watch sites. Author on the paper and a longtime volunteer at Rocky Point Bird Observatory, Dr. Daniel Dönnecke and his team looked at whether kettle size changed from 1999 through 2023.