Very large, spectacular swift of highlands in west Mexico, also descending locally to foothills and lowlands. Often in flocks, at times of hundreds, especially around waterfalls and other roosting sites. Flight fast and strong, often soaring in kettles with wings spread in paddlelike bulges. Note the very large size, thick white nape band (often visible in a side view), and slightly notched tail (tip squared when tail is spread). Varied screaming and chattering calls can suggest parakeets.