I would argue that this species does not have broad wings, instead having the slimmest wings of any N. Am. bird that is not a hummingbird or tubenose; they often appear downright scimitar-like. The "milk mustache" is a clincher if seen. Note that spring Vaux's Swifts in their fresh deep-sooty plumage can seem convincingly blackish, and at times Vaux's will glide for long moments in the manner of Black. A true Black Swift will at least occasionally fan its no-doubt tail into a vague spoony shape as it turns. The slight projection of the head forward of the wings, combined with the much greater rear-parts projection behind the wings, produces a distinctive shape. These birds are capable of migrating directly into a Beaufort 4 north breeze, scaling for long distances on set wings and only occasionally flapping to find better "purchase" on such seemingly perverse airflow.

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