ACES – Pitkin County Open Space Birding 8/18/2025

We began this outing with a view of the gorge from the top of the trail at the back of the AABC that overlooks the Roaring Fork River above Aspen Sanitation facilities. From this vantage point, we were able to see hundreds of swallows perched on utility wires spanning the gorge. The angle allowed us to see most of the birds against the landscape across the gorge, rather than backlit against the sky. As we moved down the switchbacks and the sun rose over Hunter Creek, our viewing changed and we were able to see details on closer birds even better. Based on both field marks and voices, we determined that tree, violet-green, cliff and northern rough-winged swallows were present, and that, based on unit estimation, there were likely around +/- 800 birds. It was exciting to see this abundance and to understand their migration staging and the distances they would be flying to their wintering range. These birds, some of the earliest to depart the Valley, will be leaving any day. We spent time on the switchbacks in the open shrub habitat where vireos, warblers, tanagers, catbirds, and flycatchers were foraging. Along the river, a kingfisher was actively fishing and giving flight calls, two dippers were in the river at the bridge, and Steller’s jays, nuthatches, warblers, and flycatchers were active in the riparian forest. We found great pockets of activity along the Burlingorge Trail and in Promontory Park before walking the traverse trail back to the AABC. Highlights here included watching a tanager break up and remove the stinger from a wasp before eating it, two Townsend’s solitaires, many hummingbirds, a Bullock’s oriole, and a sage thrasher. Other highlights included a golden-crowned kinglet and a brown creeper at very close range for excellent views. We ended the trip with a discussion of bill color change and the physiological mechanisms behind this seasonal appearance change. We were all happy to have seen the overall abundance of birds and the 43 species in the varied habitats of the Burlingorge loop! Join us on Tuesdays as Morning Birding continues through late summer!