Duck and chicken eggs can be incubated together, but you should consider differences in the incubation process for each including duration, required temperature, and humidity.
Egg size is an important consideration during incubation because most incubators come with turners the size of a particular egg. If the turners of your incubator are designed for chicken eggs, they might not turn duck eggs properly.
Duck egg shells are tougher than chicken eggs. Even though they appear tougher, you should not roughly handle the eggs. The texture of the egg determines the brightness of light you should use when candling (inspecting) the eggs.
Most homesteaders agree that the optimum temperature to incubate duck and chicken eggs is 99.5°F (37.5°C). When the eggs are transferred to hatcher trays (to prepare them to hatch), the temperature may reduce to 99°F (37.2°C).