Partial incubation during egg laying reduces eggshell microbial loads in eastern bluebirds, helping maintain egg viability by inhibiting microbial growth. The researchers found that eggs exposed to partial incubation had significantly lower microbial colony counts compared to eggs left in ambient conditions. This suggests that partial incubation during egg laying can enhance egg viability in eastern bluebirds by reducing the presence of potentially harmful microbes on the eggshells.