Peregrines don't build nests. They usually just find a shallow dip in some rocks or scrape a depression in the soil on the ledge of a cliff, or even use the ledge of a building. Female peregrines lay two to four eggs at a time. Parents incubate the eggs for about a month until the eggs hatch. Peregrine chicks stay in the nest for up to six weeks, by which time they've learned to fly.