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Keywords:

  • behavioural compensation;
  • delayed life-history effects;
  • Emberiza citrinella;
  • indirect effects;
  • nest predation;
  • passerine bird;
  • yellowhammer

Summary

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 yellowhammer Emberiza 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-term implications for chicks.

6.Synthesis and applications. We propose a mechanism by 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.