Sick's Swift is considered by some authorities to be a subspecies of Ashy-tailed Swift C. andrei. Other authorities consider it to be a full species while they consider C. andrei to be a sub-species of Vaux's Swift C. vauxi . All rather confusing really. 

Photo 3 shows a bird with its head tucked down showing the pale throat and photo 4 was taken in a well where some birds were roosting and some were nesting.

There are recordings on xeno-canto and additional information available via Avibase and Wikiaves.