Count estimates at Chapman School of 1,700 to 35,000 swifts have been reported. The Audubon Society provides detailed information about the annual swift watch at Chapman School, which draws a crowd each night.
These swifts typically roost in dead but still-standing, large diameter, old growth hollow grand fir (Abies grandis) trees. However, deforestation has reduced the number of available roost sites and numbers of Vaux's swifts have declined sharply since the 1980s. Other chimneys are used by the swifts throughout the area. Pendleton, Medford, Roseburg, and other Oregon locations,also have brick structures that are used annually by the birds. There are efforts in some parts to preserve chimneys that have been torn down.
References:
Evelyn L. Bull and Roy C. Beckwith (1993). Diet and Foraging Behavior of Vaux's Swifts in Northeastern Oregon. The Condor Vol. 95, No. 4, Nov.
Evelyn L. Bull (2002). The Value of Coarse Woody Debris to Vertebrates in the Pacific Northwest. USDA Forest Service Gen. Tech. Rep. PSW-GTR-181.