sounds like they are laying in the same nest, not uncommon. if they are still laying remove the oldest eggs, mark the freshest each day, leave 8-12 in the nest. They may both set but probably the runner will not set for long, they are non setters as a breed, exceptions exist.

I did a through check of the nest today. 28 eggs! It appears both girls are laying as I see half the eggs have a greenish tint and the others a pinkish tint. I will check again tomorrow to see if either are still laying. I wonder if I should try and hatch half myself?

Why not give it a try! They should be close to going to setting, at least the Mallard. Th greeish ones should be Mallard. What color are the Runners?

The runners are chocolate indian runners (but look black in color).

just trying to figure what the offspring would look like, they could be Khaki from the runner x Mallard cross. (M^D) for mallard X (d^d) for chocolate = khaki. They could still have facial stripes and white neck rings and they wont be a gopod khaki color but some phase of it anyhow.

I am wrong, maybe?? Its the dusky pattern mallard(MD) and Chocolate which make khaki, not the wild type(m+)which you probably have. I still think they will be a poor Khaki color .

Awwwww, baby ducklings! How cute! I want to see pics when they hatch, please!

Update...the female runner was taken by a coyote about 3 weeks ago. My husband has finally fenced the yard! Now down to the male Indian Runner and the female Rouen (who is setting on a clutch of 17 eggs in a new and safer spot) The eggs I brought in to incubate was doing great at 16 days until my pre-school moved the heat lamp. Sadly, I think they all died. It was 110F and I see no more movement or much progress (but can still see the blood veins)