In harder terrain it may be no more than a cavity under a pile of rocks. At some sites where constant burrowing has taken place over the years, whole areas have collapsed, rendering then untenable. The extinction of the colony on Grassholm, Wale, is a classic example of such a situation. The nest itself may be little more than a few bits of grass and the odd feather, whilst at times the egg can be deposited on bare soil. The single egg, laid during the second half of May, is dull white with a rough texture and is usually faintly marked with grey or reddish spots.
Incubation lasts for about forty days.
The newborn chick is covered in black down above and white below. When feeding their young the adults are particularly vulnerable to predation by large gulls and skuas. The Great Black-backed Gull , particularly, preys on the Atlantic Puffin and can swallow them whole. The young Atlantic Puffins are feed for about 40 days and then abandoned by their parents. Eventually, after about a week, they are driven by hunger to emerge from the nesting burrow and make their way to the sea.