Nest predation may decrease the optimal clutch size for many reasons.
In particular, a smaller clutch size may permit more investment in re-
laying or in survival to the next reproductive event. The response to
nest predation may be either genetic, as shown by comparative studies
on birds, or phenotypic, as found in several aquatic species (inverteb
rates and fish). We have studied the effects of several years of high
nest predation on clutch size variation in a Great Tit (Pants major) p
opulation. We tested whether nest predation was associated with select
ion on clutch size or with any phenotypic changes. In the year followi
ng peak nest predation, mean clutch size was reduced by about one egg.
For nest predation, adult survival, and local recruitment, we failed
to detect any dependence on clutch size; the reduction in clutch size
was mostly phenotypic. Similarly, the return of clutch size to pre-pre
dation values was explained as a phenotypic change. Surprisingly, indi
viduals that did not experience nest predation themselves also modifie
d their clutch size. This suggests that information on past predation
persisted in the population for several years. In years with reduced c
lutch size, adult survival at the population level was higher, suggest
ing that a reduction in clutch size would be adaptive in case of nest
predation, and that females adjusted their clutch size toward the opti
mum.