Kevin J. Beaty/Denverite An Audubon's yellow-rumped warbler hunts for bugs above the Denver Audubon Nature Center south of the Chatfield Reservoir. May 12, 2021. Around twelve million birds are expected to fly north and make their way across Colorado over the next few nights during the peak of spring migration. And despite any fears of flocks that Alfred Hitchcock may have instilled in you, they mean no harm. “They’re coming into North America to breed,” Zach Hutchinson of Audubon Rockies said. “So it’s an annual cycle that’s part of maximizing their ability to survive and reproduce.” In Colorado, we’re talking about Swainson's Thrushes, Bullock's Orioles, Western Tanagers, Yellow Warblers and many others that want to take advantage of the warmer, clearer weather. Most of them migrate at night, when conditions are calm, fewer predators are out and stars can help with navigation.