Factors predicting susceptibility of songbirds to nest predation by corvids

Despite the suggestion from several meta-analyses that nest predation is not limiting songbird populations, responses to experimental removal of nest predators, such as corvids, have varied. The impact of nest predation by corvids on songbird populations is unclear. One potential explanation for this disparity is that susceptibility could vary according to the nesting biology of a species. To investigate this hypothesis, we conducted a review of studies detailing nest predation on UK songbirds and extracted the reported rates of nest predation from 80 papers which attempted to identify the predators responsible. We found that corvids were significant predators of songbird nests (24% of nest predation was attributed to corvids). However, species that construct open nests, and whose breeding season overlaps considerably with the breeding season of magpie and jay, incurred the highest rate of nest predation by corvids specifically (different factors predicted predation by non-corvid predators). We then used attributes of nesting biology to predict predation rates for UK breeding species for which we found no empirical data (n = 31). Although, in most cases cited in the literature songbird populations are unaffected by changes in corvid numbers, there are some cases in which species we predicted to be more susceptible to corvid predation responded to changes in corvid numbers. However, an understanding of how of other predators and other non-predation-related factors limit both songbird breeding success and songbird population numbers is necessary in any conservation management of songbird populations.