Do birds lay eggs at a particular time of day?

Most small birds lay soon after sunrise, most likely because their eggs are relatively large compared to body size. Carrying such a big, fragile object around may make a bird more vulnerable to predators and increases the risk of damage. Larger birds, whose eggs are much smaller relative to body size, often lay at other times of day with no clear timing pattern. Some, however, are constrained by behaviour. For example, most petrels and shearwaters only return to their nesting burrows after dark, which restricts egglaying to night-time hours. Interestingly, female cuckoos – whose eggs are very small for a bird of their size – lay during the afternoon, possibly because they are less likely to be detected by their hosts, who spend more time away from the nest during these hours.

Small birds, such as nuthatches, generally lay their eggs at first light.