Abstract

1. The management of habitat structure can limit access to food and can also alter perceived predation
risk. Minimising the risk of predation, by changing behaviour, may have negative impacts similar
to predation itself across a wide range of species. Predation risk influences the behaviour of
adults foraging for altricial young, so that they avoid disclosing the location of their offspring to
predators. The consequences of these behavioural changes for offspring are unknown.
2. We investigate whether predator-induced changes in provisioning rates can have impacts upon
avian nestlings through reductions in growth and condition, and whether this is influenced by
resource availability, using the declining yellowhammerEmberiza citrinella as a model species.
3. We show a sizeable negative impact of nest predator activity upon brood provisioning rate, indicating
that parents can assess nest predation risk and adjust their behaviour accordingly.
4. Chick condition and growth were both negatively influenced by corvid nest predator abundance
and positively influenced by food abundance in large broods, suggesting that parents raising large
broods in unfavourable conditions were unable to compensate fully for the effect of corvid activity
on provisioning rate.
5. In areas of low food availability, corvid abundance was associated with reduced chick growth
and condition; in areas of higher food availability no association was found indicating that where
food resources are abundant, parents can compensate for reductions in provisioning rate when corvids
are active, with no long-termimplications for chicks.
6. Synthesis and applications. We propose a mechanismby which two distinct trends linked with the
intensification of agriculture, namely increasing corvid abundance combined with a decreasing food
supply, may have indirectly precipitated population declines in farmland passerines through
delayed life-history effects across generations. As the impacts of corvids are reduced where invertebrates
are abundant, we suggest that management should concentrate on improving the quality of
foraging habitat by creating mosaics of long and short vegetation, rather than on the control of corvids.
This will allow adult birds to compensate for the indirect effects of high corvid abundance by
increasing their provisioning effort when nest predation risk is low and thus buffer any long-term
consequences for nestlings.