Authors: Fenn, Sarah; Bignal, Eric;Bignal, Sue;Trask, Amanda;McCracken, Davy;Monaghan, Pat;Reid, Jane;

Effective conservation of threatened populations requires targeted and evidence-based mitigation of key demographic constraints that limit population viability. However, realised population-wide impacts of conservation interventions may be complex, with conservation outcomes depending on both temporal variation in impacts on target individuals, and impacts on non-target conspecifics (e.g. different age classes). Yet, such impacts are rarely quantified, hindering robust assessment of conservation efficacy.

Using a long-term demographic dataset on the threatened Scottish red-billed chough (Pyrrhocorax pyrrhocorax) population, we quantified the demographic consequences of a multi-year (2010-2018) supplementary feeding programme on target juvenile survival, and assessed collateral impacts on non-target adults. Multi-state mark-recapture analyses show that management successfully increased juvenile survival, but that efficacy varied both within and among years. Furthermore, before-after control-impact analyses showed that feeding increased the probabilities of adult survival and successful reproduction, with substantial population-level benefits. Consequently, the supplementary feeding intervention substantially increased the probability of population persistence. This case study of science-informed conservation management demonstrates that supplementary feeding, a widely used conservation tool, can have strongly beneficial conservation effects, and illustrates how full assessment of intervention impacts can affect assessment of short-term efficacy and thereby subsequent management decisions.