Asynchronous and synchronous hatching: effect on early growth and survivorship of Herring Gull, Larus argentatus, chicks

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Abstract
The adaptive significance of asynchronous hatching in the Herring Gull, Larus argentatus, was examined during the summer of 1984 at Kent Island, New Brunswick. Chick growth and behaviour in 28 experimental three-egg clutches in which the eggs hatched synchronously (i.e., hatch interval ≤ 24 h between the first (A chick) and last (C chick) hatched) were compared with that of 15 control three-egg nests with normal hatching asynchrony (A–C hatch interval > 24 h). All chicks had similar hatch weights, except for control C chicks, which on average were significantly lighter than their nest mates and experimental chicks. Growth rates were also similar for all chicks within and between groups, except for control C chicks, which grew at a significantly slower rate compared with nest mates and experimental chicks. In control broods, C chicks disappeared first significantly more often than A or B chicks. In experimental broods, a similar proportion of A, B, and C chicks disappeared first. Survivorship, through to day 5 posthatch, was significantly lower for control C chicks than for control A and B chicks as well as experimental chicks. These results suggest that the benefit Herring Gulls achieve hatching their eggs asynchronously results from the competitive advantage accrued to the A chick (and the B chick to some degree), which allows them to obtain more food, especially during periods of food stress. Subsequently the probability of survival of the older, more fit chick(s) is enhanced.