Raptor reintroductions: Cost-effective alternatives to captive breeding.

Reintroductions are becoming a popular tool to prevent extinctions, although their overall success rate is low. Assessing the efficiency and cost-effectiveness of different reintroduction strategies may help identify and promote efficient practices. Captive-breeding is widely used in animal reintroductions, although concerns have been raised about relatively high failure rates and economic costs. Here, we compared the effectiveness of two simultaneously used strategies in the reintroduction of the Bonelli's eagle on the island of Mallorca: The release of captive-bred chicks and wild-reared, translocated non-juveniles. To do so, we estimated the main vital rates for individuals released by both strategies and used these to perform population simulations to assess their overall performances. The use of wild-reared nonjuveniles showed a trend with higher numbers of breeding pairs 10 years after the end of releases (14.75 pairs, 95% CI 4-25 vs. 11.21 pairs, 95% CI 2-24) and was the only strategy that prevented extinction in the long term. Following that, based on cost estimations of every strategy and different reintroduction budgets, we assessed the cost-effectiveness of releasing wild-reared non-juveniles compared with two captive-breeding alternatives: Releasing chicks either originally from breeding programmes or extracted from nests in natural populations. Again, releasing wild-reared non-juveniles was the only strategy that prevented long-term extinction in all economic scenarios (i.e. low-budget scenario 21.49 pairs, 95% CI 2-25). The use of chicks sourced from captive-breeding programmes did not guarantee long-term persistence even in high-budget scenarios (14.50 pairs, 95% CI 0- 25). Releasing wild-reared non-juveniles boosts early recruitment to the breeding population and early reproduction, which can be key for reintroduction success. However, in some scenarios, post-release effects can be stronger in wild-reared individuals, especially because of high translocation stress and post-release dispersal. Hence, we recommend undertaking careful evaluation of the pros and cons of every strategy and embracing adaptive management to choose best strategies

Joint estimation of survival and dispersal effectively corrects the permanent emigration bias in mark‑recapture analyses

Robust and reliable estimates of demographic parameters are essential to understand population dynamics. Natal dispersal is a common process in monitored populations and can cause underestimations of survival and dispersal due to permanent emigration. Here, we present a multistate Bayesian capture-mark-recapture approach based on a joint estimation of natal dispersal kernel and detection probabilities to address biases in survival, dispersal, and related demographic parameters when dispersal information is limited. We implement this approach to long-term data of a threatened population: the Bonelli's eagle in Catalonia (SW Europe). To assess the method's performance, we compare demographic estimates structured by sex, age, and breeding status in cases of limited versus large data scales, with those of classical models where dispersal and detection probabilities are estimated separately. Results show substantial corrections of demographic estimates. Natal dispersal and permanent emigration probabilities were larger in females, and consequently, female non-breeder survival showed larger differences between separate and joint estimation models. Moreover, our results suggest that estimates are sensitive to the choice of the dispersal kernel, fat-tailed kernels providing larger values in cases of data limitation. This study provides a general multistate framework to model demographic parameters while correcting permanent emigration biases caused by natal dispersal

Assumptions about survival estimates and dispersal processes can have severe impacts on population viability assessments

Population viability analysis (PVA) is a central tool for conservation decision-making. To ensure the reliability of PVA projections, it is important to identify factors that can introduce biases. This study addresses two general but overlooked related issues in PVAs that can significantly affect the reliability of their projections. First, we examined the effects of using apparent versus true survival estimates on PVA outcomes. Second, we incorporated emigration and immigration into the models to assess their influence on the accuracy of projections based on each type of survival estimate. To evaluate these concerns, we implemented PVAs structured by age, sex, and breeding status using as a study system a threatened raptor population (Bonelli's eagle, Aquila fasciata) from which apparent and true survival were available (2008–2020). The performances of PVA projections based on each survival type and dispersal process were assessed by evaluating their fit to census data. Our findings revealed that using apparent survival underestimated census data, while true survival showed a considerably better fit. However, models including dispersal processes showed that each survival type may only deliver precise projections at very specific levels of emigration and immigration. Given the potentially large differences found when using true and apparent survival, we suggest that the relevance of this issue should be elevated to that of other widely reported PVA limitations. Recently developed, accessible analytical methods may permit an easier estimation of true survival and dispersal processes. Otherwise, calibrating projections against observed data may be fundamental to test the adequacy of survival estimates

Assumptions about survival estimates and dispersal processes can have severe impacts on population viability assessments

Population viability analysis (PVA) is a central tool for conservation decision-making. To ensure the reliability of PVA projections, it is important to identify factors that can introduce biases. This study addresses two general but overlooked related issues in PVAs that can significantly affect the reliability of their projections. First, we examined the effects of using apparent versus true survival estimates on PVA outcomes. Second, we incorporated emigration and immigration into the models to assess their influence on the accuracy of projections based on each type of survival estimate. To evaluate these concerns, we implemented PVAs structured by age, sex, and breeding status using as a study system a threatened raptor population (Bonelli's eagle, Aquila fasciata) from which apparent and true survival were available (2008–2020). The performances of PVA projections based on each survival type and dispersal process were assessed by evaluating their fit to census data. Our findings revealed that using apparent survival underestimated census data, while true survival showed a considerably better fit. However, models including dispersal processes showed that each survival type may only deliver precise projections at very specific levels of emigration and immigration. Given the potentially large differences found when using true and apparent survival, we suggest that the relevance of this issue should be elevated to that of other widely reported PVA limitations. Recently developed, accessible analytical methods may permit an easier estimation of true survival and dispersal processes. Otherwise, calibrating projections against observed data may be fundamental to test the adequacy of survival estimates

Egyptian Vulture CR data

This dataset was used to analyze survival probabilities of Egyptian Vultures at Canary Islands from 1998 to 2017.We acknowledge financial support through the projects REN 2000–1556 GLO, CGL2004-00270/BOS, CGL2009-12753-C02-02, CGL2012-40013-C02-01, and CGL2015-66966-C2-1-2-R (Spanish Ministry of Economy and Competitiveness and EU/FEDER).The data file contains capture, resight and recovery histories of Egyptian vultures at Canary Islands (Fuerteventura and Lanzarote) during breeding seasons 1998 to 2017. This file contains one line per individual; one column per encounter occasion (from column 1 to 20 were code “0” indicate that the individual was not observed in a particular year; code “1” is used for individuals detected (marked at capture or resighted) with both coloured and steel metal butt-end rings; code “2” is used for individuals detected (marked at capture or resighted) with coloured and steel metal lock-on rings; code “3” is used for individuals resighted only retaining their coloured rings, code “4” is used for individuals resighted only retaining steel metal butt-end rings; and code “5” is used for individuals recovered freshly dead. There are six further columns (21 to 26) indicating the group (starting age at marking form 1-year-old to ≥6 year-old) for each individual.N

Evaluating European LIFE conservation projects: Improvements in survival of an endangered vulture

Long-lived avian scavengers are threatened worldwide and thus, are common targets of conservation plans. However, scientific evidence of both the factors limiting populations and effectiveness of management actions are greatly needed in order to develop more efficient and successful conservation strategies. We assessed the effectiveness of conservation actions applied within a LIFE-Nature project aimed at improving the long-term survival of the critically endangered Canarian Egyptian vulture: including education campaigns for public awareness and control of illegal poisoning and the modification of power lines to reduce the risk of accidents. We formulated a multievent capture–mark–recapture model to obtain estimates of survival for juvenile, subadult and adult birds accounting for probabilities of resight, recovery and losses of metal and colour rings. Models supported a substantial enhancement in survival for subadult and adult birds and a moderate improvement for juveniles after the implementation of LIFE actions. Ring loss probabilities became notably high in the middle to long term. Poisoning events became very rare after LIFE was implemented, suggesting a positive effect of environmental education and awareness campaigns. Entanglements and collisions in power lines were also efficiently mitigated. Instead, electrocutions became the most identified cause of death in the post-LIFE stage. Synthesis and applications. Our results highlight the improvement of survival in a threatened island vulture population after the implementation of a European LIFE conservation project. On small islands, with small human populations and few stakeholders, education and awareness campaigns can be especially effective for biodiversity conservation. We also demonstrate the need to complement conservation programmes with long-term monitoring, which is essential to evaluate the effectiveness of actions, especially for long-lived species.Peer reviewe