EGG-PRODUCTION CONSTRAINTS AND THE EVOLUTION OF AVIAN CLUTCH SIZE

The aim of this study was to examine whether the capacity of female bi rds to produce high quality eggs could act as a constraint on the evol ution of clutch size. By removal of the first laid egg; lesser black-b acked gulls were experimentally induced to lay an additional egg. Thei r breeding success was then compared with a control group rearing the same clutch and brood size, The survival of chicks from the additional egg was only about a quarter of that of chicks from last laid eggs in the control group; it was found that this was largely an effect of re duced hatchling mass. The limited egg production capacity of females d emonstrated by this experiment may in part explain discrepancies betwe en predicted optimal and observed modal clutch sizes in birds.