Reduction of genetic diversity in 'Alalā (Hawaiian crow; Corvus hawaiiensis) between the late 1800s and the late 1900s

Genetic and genomic data are increasingly used to aid conservation management of endangered species by providing insights into evolutionary histories, factors associated with extinction risks, and potential for future adaptation. For the 'Alalā, or Hawaiian crow (Corvus hawaiiensis), genetic concerns include negative correlations between inbreeding and hatching success. However, it is unclear if low genetic diversity and inbreeding depression are consequences of a historical population bottleneck, or if 'Alalā had historically low genetic diversity that predated human influence, perhaps as a result of earlier declines or founding events. In this study, we applied a hybridization-based sequence capture to generate a genome-wide single nucleotide polymorphism (SNP) dataset for comparing historical specimens collected in the 1890s, when 'Alalā were more numerous, to samples taken between 1973 and 1998, when 'Alalā population densities were near the lowest documented levels in the wild, prior to all individuals being collected for captive rearing. We found low genome-wide diversity in both sample groups, however, the modern sample group (1973 to 1998 cohort) exhibited relatively fewer polymorphic alleles, a lower proportion of polymorphic loci, and lower observed heterozygosity, consistent with a population decline and potential bottleneck effects. These results combined with a current low population size highlight the importance of continued efforts by conservation managers to mitigate inbreeding and maintain founder representation to preserve what genetic diversity remains.

Adapting conservation breeding techniques using a data-driven approach to restore the 'Alalā (Hawaiian crow, Corvus hawaiiensis)

For some critically endangered species, conservation breeding is a vital steppingstone toward re-establishing wild populations. The 'Alalā (Hawaiian crow, Corvus hawaiiensis), currently extinct in the wild, exists today only in a conservation breeding program, which, for many years, utilized successful hands-on husbandry approaches such as separating and resocializing pairs, providing partially manmade nests, artificially incubating eggs, and puppet rearing nestlings. Yet, a top priority of any conservation breeding program is to retain natural behaviors essential to postrelease survival and reproduction, to achieve successful reintroduction and restoration to the wild. We describe how we are adapting 'Alalā husbandry techniques to strengthen pair bonds through full-time socialization, enable pairs to build robust nests, encourage females to incubate eggs to hatch, and provide pairs and their offspring with vital parental rearing experiences. We discuss the use of standardized, data-driven methods to objectively track our progress towards successful parental breeding and to select release candidates based on their likelihood to survive and breed in the wild. The information shared in this report can be applied to other conservation breeding programs, particularly those implementing or transitioning to husbandry techniques geared towards preparing species to thrive in the wild.

Anti-Predator Vigilance as an Indicator of the Costs and Benefits of Supplemental Feeding in Newly Released ‘Alalā (Corvus hawaiiensis)

Although supplemental feeding is commonly used as a conservation strategy during animal translocations, it comes with a number of pros and cons which can be hard to quantify. Providing additional food resources may lead to improved physical health, survivorship, and reproduction. However, offering predictable food sources could make individuals more conspicuous to predators and less aware of their surroundings, disrupting their natural predator-prey dynamic. Decisions such as release cohort size and supplemental feeder design could influence the balance of these costs and benefits, depending on how animals behave in the face of predation risk and static food sources. Additionally, animals released to the wild from long term human care must balance foraging and predation risk while adjusting to a novel environment. To help conservation managers make informed decisions in light of these potential costs, we studied the behavior of a cohort of 11 conservation-bred ‘alalā (Corvus hawaiiensis) at supplemental feeding stations after release into the wild. Vigilance, foraging behavior and social group size was quantified via 1,320 trail camera videos of ‘alalā over the span of 12 months. We found that vigilance increased over time since release, suggesting that ‘alalā learn and adjust to their novel surroundings. Both vigilance and eating decreased with group size, indicating that although conspecifics may share the burden of scanning for threats, they also increase competition for food. We also found that the design of the feeder may have limited birds' abilities to express anti-predator behavior since less vigilance was observed in individuals that manipulated the feeder. Yet, birds may have been able to offset these costs since they increasingly scrounged for food scraps next to the feeder as time progressed. We discuss how changes to behavior over time, social interactions, and feeder design should all be considered when planning supplemental feeding as part of wildlife translocations.

Moving from trends to benchmarks by using regression tree analysis to find inbreeding thresholds in a critically endangered bird

Understanding how inbreeding affects endangered species in conservation breeding programs is essential for their recovery. The Hawaiian Crow ('Alalā) (Corvus hawaiiensis) is one of the world's most endangered birds. It went extinct in the wild in 2002, and, until recent release efforts starting in 2016, nearly all of the population remained under human care for conservation breeding. Using pedigree inbreeding coefficients (F), we evaluated the effects of inbreeding on Hawaiian Crow offspring survival and reproductive success. We used regression tree analysis to identify the level of inbreeding (i.e., inbreeding threshold) that explains a substantial decrease in 'Alalā offspring survival to recruitment. Similar to a previous study of inbreeding in 'Alalā, we found that inbreeding had a negative impact on offspring survival but that parental (vs. artificial) egg incubation improved offspring survival to recruitment. Furthermore, we found that inbreeding did not substantially affect offspring reproductive success, based on the assumption that offspring that survive to adulthood breed with distantly related mates. Our novel application of regression tree analysis showed that offspring with inbreeding levels exceeding F = 0.098 were 69% less likely to survive to recruitment than more outbred offspring, providing a specific threshold value for ongoing population management. Our results emphasize the importance of assessing inbreeding depression across all life history stages, confirm the importance of prioritizing parental over artificial egg incubation in avian conservation breeding programs, and demonstrate the utility of regression tree analysis as a tool for identifying inbreeding thresholds, if present, in any pedigree-managed population.

Animal Welfare in Conservation Breeding: Applications and Challenges

Animal welfare and conservation breeding have overlapping and compatible goals that are occasionally divergent. Efforts to improve enclosures, provide enriching experiences, and address behavioral and physical needs further the causes of animal welfare in all zoo settings. However, by mitigating stress, increasing behavioral competence, and enhancing reproduction, health, and survival, conservation breeding programs must also focus on preparing animals for release into the wild. Therefore, conservation breeding facilities must strike a balance of promoting high welfare, while minimizing the effects of captivity to increase population sustainability. As part of the Hawaii Endangered Bird Conservation Program, San Diego Zoo Global operates two captive breeding facilities that house a number of endangered Hawaiian bird species. At our facilities we aim to increase captive animal welfare through husbandry, nutrition, behavior-based enrichment, and integrated veterinary practices. These efforts help foster a captive environment that promotes the development of species-typical behaviors. By using the "Opportunities to Thrive" guiding principles, we outline an outcome-based welfare strategy, and detail some of the related management inputs, such as transitioning to parental rearing, and conducting veterinary exams remotely. Throughout we highlight our evidence-based approach for evaluating our practices, by monitoring welfare and the effectiveness of our inputs. Additionally we focus on some of the unique challenges associated with improving welfare in conservation breeding facilitates and outline concrete future steps for improving and evaluating welfare outcomes that also meet conservation goals.