R. J. Greenwood 1969 <p>The eggs of early-nesting waterfowl in North Dakota are frequently exposed to subfreezing temperatures. Mallards (<i>Anas platyrhynchos</i>) and Pintail (<i>Anas acuta</i>), normally the first ducks to arrive in the spring, begin limited early nesting in min-April. Nighttime temperatures during this period frequently drop below freezing, and late spring blizzards are not unusual.</p> application/pdf 10.2307/4083468 en American Ornithological Society Mallard hatching from an egg cracked by freezing article