Rb. Bradbury et R. Griffiths, Sex-biased nestling mortality is influenced by hatching asynchrony in the Lesser Black-backed Gull Larus fuscus, J AVIAN BIO, 30(3), 1999, pp. 316-322
Many birds hatch their eggs asychronously while other species are more sync
hronous. Different hatching patterns may produce different sex-ratios throu
gh sex-biased chick mortality, but the relationship between sex-ratios and
hatching pattern has received little attention. An extreme food shortage in
a Lesser Black-backed Gull colony allowed us to examine the timing of mort
ality of nestlings relative to sex and to hatching order. This was carried
out in experimentally-created synchronous and asynchronous broods. when the
latter mimicked the normal hatching spread. Unambiguous sexing was facilit
ated by use of molecular methods. In asynchronous broods, last-hatched fema
le chicks survived significantly longer than last-hatched male chicks, whil
st the males significantly out-lived the females among the earlier-hatched
chicks. Then was no difference in survival time of the sexes in synchronous
breeds. This suggests that chick sex-ratio is, at least partly, a function
of asynchrony. Production of skewed sex-ratios via sex-biased mortality sh
ould be considered when evaluating the merits of asynchrony and synchrony.