Effects of early incubation constancy on embryonic development: An experimental study in the herring gull Larus argentatus

1.In many birds, parental nest attendance in early incubation is variable, with eggs incubated only intermittently. The effect of this on chick hatching success is unknown.2.We allowed clutches of a semi-precocial species, the herring gull, to experience different levels of early incubation constancy and examined the effects on embryonic development and hatching.3.We found evidence that high early incubation constancy enabled some eggs to develop and hatch faster. Chicks that experienced high thermal constancy during early incubation had heavier body mass at hatching.4.We discuss the factors that might constrain parental attendance early in incubation.