CACK-A-CACK. Duck-like quacking or cackling, several harsh notes given in rapid succession : cack-a-cack or cack-a-hack, or craw-aw-auk. often repetitive: r-r-racket, r-r-racket, r-r-racket. Little carrying power. Also compared to round stones being clacked together
PREEP. Single, clear, piercing, high-pitched, bird-like prreep that slurs upward at the end, given about once per second. From a distance, collective sound is like sleigh bells jingling. Closer, seems deafening.
CHU-HU-HU-HUCK. A series of 5 or more (sometimes 3-5) gutteral “chucking” notes or croaks, delivered as a stutter usually too fast to count: chu-hu-hu-hu-huck, chu-hu-hu-hu-huck, chu-hu-hu-hu-huck. Also described as a short chuckle-like guttural trill, or like the sound of rubbing a balloon
DREAMY TEMOLO. High, sweet, dreamlike tremolo, lasting several to 30 seconds or more, pausing for a few seconds, and then repeated. Can be imitated by whistling and humming a high note at the same time. Calls day and night during peak breeding season