2. We used 15 years of individual-based demographic data in a “before-after control-impact” (BACI) analysis to quantify collateral demographic impacts of a targeted multi-year supplementary feeding programme designed to increase sub-adult survival and hence viability of a small, threatened red-billed chough (Pyrrhocorax pyrrhocorax) population. Specifically, we assessed whether the intervention also affected adult survival and reproductive success, and whether such collateral effects were themselves sufficient to stabilise population size and hence achieve short-term conservation aims.
3. The probabilities of adult survival and successful reproduction increased substantially between the “before-feeding” and “during-feeding” periods in those choughs associated with supplementary feeding, but not otherwise. Overall breeding success (i.e. number of chicks fledged per occupied territory) also tended to increase, even though brood sizes did not increase. These relationships, which were detectible only through BACI analyses, suggest that supplementary feeding targeted at sub-adults had unplanned positive impacts on adult demographic rates.
4. Deterministic matrix models designed to project population growth demonstrate that these estimated collateral effects were sufficient to make a substantial contribution to increasing population growth rate and achieving short-term population stability.
5. Synthesis and applications: Our results indicate substantial positive collateral impacts of a targeted supplementary feeding intervention on population viability, despite no a priori expectation that the non-target adults were food-limited. This case-study illustrates how thorough assessment of collateral impacts of targeted interventions can affect assessment of short-term efficacy and reveal new opportunities for future interventions, thereby informing subsequent management decisions.
We thank all Islay landowners and farmers who allowed access to nest sites and supported supplementary feeding, in particular Sue Bignal, Donald Jones and Robert and Tom Epps, and everyone who contributed to fieldwork and data collection. We thank Scottish Natural Heritage (SNH), particularly Rae McKenzie, Jess Shaw and Des Thompson, and Royal Society for the Protection of Birds, for their ongoing support and for funding supplementary feeding. S.R.F was funded by a Natural Environment Research Council iCASE studentship (NE/P009719/1) supported by SNH. A.E.T was funded by SNH. D.I.M was supported by the Scottish Government’s 2011-2016 and 2016-2021 Strategic Research Programmes.
- Adaptive management
- adult survival
- annual reproductive success
- before-after control-impact
- evidence-based conservation
- population growth rate
- supplementary feeding
- adaptive management
- RED-BILLED CHOUGH
- BREEDING SUCCESS
- FOOD SUPPLEMENTATION
- OFFSPRING SEX-RATIO
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Collateral benefits of targeted supplementary feeding on demography and growth rate of a threatened population
Fenn, S. (Creator), Bignal, E. M. (Creator), Trask, A. E. (Creator), McCracken, D. (Creator), Monaghan, P. (Creator) & Reid, J. (Creator), Dryad Digital Repository, 6 Aug 2020