HELP! A female mallard duck left 12 eggs in my yard and has nurtured them for a few weeks. She has been gone for over a day now and the temperature is going below freezing tonight. High winds bring the wind chill to -9 °C (15 °F). Is this normal? Will she come back or should I take care of the babies myself? Thanks in advance!
At this point in time the chicks (if there ever were some in the eggs) are certainly dead.
Duck eggs need to be kept in a very narrow range of temperature to develop and the incubation time is 21 - 31 days. This period is very stressful for the mother, because she has to constantly turn and shift the eggs around to keep them at the same temperature, but she also has to eat and defend the nest from predators. If the male is killed or abandons her, she might have to give up the nest to ensure her own survival.
On average, females leave the nest three times per day, and each recess lasts about an hour.
Source and more information: Ducks Unlimited
So a duck leaving a nest for several hours means that she won't come back, or if she does return, the eggs are much to cold and the embryos already died.
There's also the possibility that the mother never mated or is infertile and the eggs weren't fertilized. Most birds have a rough idea about how long the chicks would normally take to hatch and when nothing happens after that time, they abandon the nest.
One side note: if you find a duck nest and there's no bird around, you should not touch the nest and leave it alone. If the mother is taking a break to eat or waits nearby, she needs free access to her nest to return. If she's disturbed too often, she could abandon her eggs.