Pacific Commons Linear Park (8/8/20) - Possible Chimney Swift

Jerry Ting

This (8/8/2020) morning I saw a possible Chimney Swift at the large pond picnic area (37.493236, -121.983744) in Pacific Commons Linear Park in Fremont. It was flying with other swallows and I first noticed its darker underparts then the darker rump compared with Vaux's Swift. Less contrast between the dark auricular and the underparts. It also shows the more bulging inner primaries compared with VASW's more evenly tapered and straight-edged wings.
Some shots can be seen in my eBird checklist here:

Stay Safe and Happy Birding
Jerry Ting,

Michael Park

Here's a guide to judging the wingshape characters mentioned by Jerry.

Judge for yourself. Vocalizations are distinct between Vaux's and Chimneys swifts, but are not noted in the report.

The wing's look broad, the secondaries do not seem to bulge significantly, and the primary shape appear relatively linear. The photos are very nice for seeing these characters.\

David Sibley refutes his previously published notions of relative tail lengths in the linked web page. This illusionary difference may be the result of the narrower wing in Chimney Swift.

Michael Park