Collateral benefits of targeted supplementary feeding on demography and growth rate of a threatened population

Abstract

1. Effective evidence-based conservation requires full quantification of the impacts of targeted management interventions on focal populations. Such impacts may extend beyond target individuals to also affect demographic rates of non-target conspecifics (e.g. different age classes). However, such collateral (i.e. unplanned) impacts are rarely evaluated despite their potential to substantially alter conservation outcomes. Subsequent management decisions may then be poorly informed or erroneous. 2. We used 15 years of individual-based demographic data in a 'before-after controlimpact' (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 stabilize 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.

Within‐year and among‐year variation in impacts of targeted conservation management on juvenile survival in a threatened population

“…Nevertheless, at face value, our estimates suggest that the intervention effects on juvenile survival were sufficient to reduce (but not prevent) population decrease. Previous analyses showed that the intervention also had substantial collateral benefits, by increasing adult survival probability and components of reproductive success (Fenn et al., 2020). Together, these results imply that the intervention successfully prevented a rapid population decline (Trask et al., 2019).…”

Integrating advances in population and evolutionary ecology with conservation strategy through long‐term studies of red‐billed choughs

“…Cook et al, 2013;Toomey et al, 2016;Williams et al, 2020). To fulfil academic objectives, primary scientific papers were strategically published in British Ecological Society journals, targeted at general concept-led international audiences spanning pure and applied ecology (Journal of Animal Ecology: Reid et al, 2003aReid et al, † , 2003bReid et al, ‡ , 2004Reid et al, , 2006Reid et al, , 2008Reid et al, , 2010Trask et al, 2016Trask et al, † , 2017Journal of Applied Ecology: Reid et al, 2011;Trask et al, 2019;Fenn et al, 2020Fenn et al, , 2021; total >685 citations, Google Scholar October 2021, Elton prize ‡ winner, † highly commended). Yet, while these papers retained some system-specific context, the focus on general conceptual rather than system-specific impact (as required for these BES journals) meant that the full process of pure-applied integration and its application to chough conservation was not previously visible.…”

“…Such analyses are widely advocated, especially where formal experiments are impossible, but still relatively rarely implemented (Christie et al., 2019). We showed that adults that attended feeding sites had higher annual survival probabilities, and higher probabilities of successful reproduction, than adults occupying the same territories in previous years, while adults currently occupying other territories did not (Fenn et al., 2020). The estimated increases in adult survival were substantial and, alongside estimated moderate increases in nest success, were almost sufficient to maintain λ close to one and hence maintain population stability (Fenn et al., 2020).…”

“…Consequently, we used individual-based models incorporating inbreeding depression alongside environmental and demographic stochasticity to examine the degrees to which ecological management to improve habitat and increase food abundance, and/or genetic management to reduce inbreeding, could increase λ and ultimately population size (Trask et al, 2019). Models were parameterised using spatially structured estimates of baseline vital rates from the long-term demographic monitoring (Reid et al, 2004(Reid et al, , 2006, and used the estimated effects of supplementary feeding as a proxy for how much vital rates could potentially be increased through habitat management (Fenn et al, 2020(Fenn et al, , 2021Trask et al, 2020). The population-wide degree of inbreeding was estimated from microsatellite variation.…”

“…During 2001-2021, we completed one major iteration of the desired sequence of (a) rigorous scientific investigation of population ecology, demography and genetics (Reid et al, 2003a(Reid et al, , 2003b(Reid et al, , 2004(Reid et al, , 2006Trask et al, 2016Trask et al, , 2017 with targeted follow-up investigation of ecological and genetic constraints (Reid et al, 2008(Reid et al, , 2009(Reid et al, , 2011Trask et al, 2017;Wenzel et al, 2011Wenzel et al, , 2012, (b) resulting evidencebased intervention Trask et al, 2020) and (c) rigorous quantitative evaluation of efficacy (Fenn et al, 2020(Fenn et al, , 2021Trask et al, 2019). This work is now informing full costing and prioritisation of future chough conservation strategy in Scotland, including decisions on increases or cessation of investment in conservation actions, encompassing future agri-environment schemes and translocations (Trask et al, 2020;Appendix S1).…”