Is nest predator exclusion an effective strategy for enhancing bird populations?

Evidence suggests that nest predation is a serious problem for the conservation of bird populations. Managers are, therefore, faced with decisions of whether to intervene to reduce this impact and if so what interventions to use. Nest predator exclusion is one of the most widely used methods for reducing predation, particularly for ground-nesting species, but studies testing its effectiveness have shown mixed results. We used explicit systematic review methodology to determine the impact of nest predator exclusion on hatching success. We used meta-analysis to summarise results from 16 predator exclusion studies. We also investigated whether factors relating to characteristics of the prey, predator species, location and study methodology explained heterogeneity in effect sizes. Predator exclusion using either exclusion fences or nest-cages resulted in a significant increase in hatching success. This was the case for declining as well as increasing bird populations indicating that nest predator exclusion is an effective method of increasing hatching success of vulnerable species. Nest-cages had a larger effect on hatching success than exclusion fences, although this difference was not significant and additional nest-cage studies are required as sample sizes were small. Heterogeneity in effect sizes was not explained by any of the covariates investigated. Studies have shown that nest-cages can lead to increased levels of predation on incubating adults and so should be used with caution especially within small populations. Research is required to determine whether increased hatching success following nest predator exclusion results in increased breeding populations as improving hatching success alone does not ensure improved conservation status of bird populations.