nother possible mechanism for is the mesopredator release effect. In the absence of apex predators, mid-ranking predators can take over the ecological role of apex predators in the food web \cite{SOULE_1988}. In unfragmented habitats, apex predators can exert top down ecological control of an ecosystem, which has indirect benefits on prey populations by suppressing mid-level predators \cite{Elmhagen_2007}. However, larger species are more vulnerable to habitat fragmentation due to the larger range size, meaning mesopredator release may become a growing problem for an increasingly fragmented U.K. forest habitat \cite{Prugh_2009}. This in turns suggests that apex predator control measures may be a valid conservation mechanism for ground nesting bird populations through top-down control of rodent populations.
FIND OUT WHERE THIS SHOULD GO -> Nest predation is the most common cause of nest failure, and previous experiments in the U.S. have found over 75% of ground nest predations are caused by terrestrial rodents \cite{Sanders_2019}. These results are slightly higher than our experiment (63%), however this suggests a possible future avenue of study in this area should aim to examine the populations of apex predators and mesopredators in this woodland, and examine whether the mesopredator release hypothesis is a good fit for these findings.
Limitations
Artificial nest experiments have inherent flaws, and the results are not always directly applicable to wild bird populations. Artificial nests can overestimate predation rates, by attracting different predators and do not mimic the seasonal variation in predation rates observed in natural nest experiments \cite{Zanette_2002,WEIDINGER_2008}. The cryptic nature of artificial nests may provide a source of bias during fixed nest experiments, especially if there are associated sensory cues. While olfactory cues from the plasticine eggs in this experiment was controlled for, the artificial nests were made from non-native conifer leaves, which may have guided predators towards the nests.
Acknowledgements
I would like to thank Cristina Banks-Leite of Imperial College London for help and advice regarding the pilot study, statistical analysis and invaluable guidance. I would also like to thank the technical staff at Silwood Park for their assistance using the GPS unit for spatial analysis. Many thanks to the Biology Undergraduate department, without whom this project could not be possible.