Position in the laying order has sex-specific consequences for reproductive success in adult black-headed gulls

Mothers who produce multiple offspring within one reproductive attempt
often allocate resources differentially; some maternally-derived
substances are preferentially allocated to last-produced offspring and
others to first-produced offspring. The combined effect of these different
allocation regimes on the overall fitness of offspring produced early or
late in the sequence is not well understood, partly because production
order is often coupled with birth order, making it difficult to separate
effects of pre-natal maternal allocation from those of post-natal social
environments. In addition, very little is known about the influence of
laying order on fitness in later-life. In this study, we used a
semi-natural captive colony of black-headed gulls to test whether an
offspring’s position in the laying order affected its early life survival
and later life reproductive success, independent of its hatching order.
Later-laid eggs were less likely to hatch, but among those that did,
survival to adulthood was greater than that of first-laid eggs. In
adulthood, the laying order of females did not affect their likelihood of
breeding in the colony, but male offspring hatched from last-laid eggs
were significantly less likely to gain a breeding position than
earlier-laid males. In contrast, later-laid female parents hatched lower
proportions of their clutches than first-laid females, but hatching
success was unrelated to the laying order of male parents. Our results
indicate that gull mothers induce complex and sex-specific effects on both
the early survival of their offspring and on long-term reproductive
success through laying order effects among eggs of the same breeding
attempt.