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.

中文翻译：

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通过使用回归树分析找到极度濒危鸟类的近亲繁殖阈值，从趋势转向基准

了解近亲繁殖如何影响保护育种计划中的濒危物种对于它们的恢复至关重要。夏威夷乌鸦 ('Alalā) ( Corvus hawaiiensis ) 是世界上最濒危的鸟类之一。它于 2002 年在野外灭绝，直到最近于 2016 年开始的放生工作，几乎所有的种群都在人类照料下进行保护繁殖。使用系谱近交系数 ( F)，我们评估了近亲繁殖对夏威夷乌鸦后代存活和繁殖成功的影响。我们使用回归树分析来确定近亲繁殖水平（即近亲繁殖阈值），这解释了 'Alalā 后代存活到招募的显着下降。与之前在 'Alalā 进行的近亲繁殖研究类似，我们发现近亲繁殖对后代存活有负面影响，但亲本（与人工）卵孵化提高了后代的存活率。此外，我们发现近亲繁殖并没有实质性地影响后代的繁殖成功，这是基于这样的假设，即存活到成年的后代会与远亲的配偶繁殖。我们对回归树分析的新应用表明，近交水平超过F 的后代= 0.098 与更多的远交后代相比，招募后存活的可能性要低 69%，为正在进行的种群管理提供了特定的阈值。我们的结果强调了在所有生命史阶段评估近交衰退的重要性，确认了在鸟类保护育种计划中优先考虑亲本而非人工卵孵化的重要性，并证明了回归树分析作为识别近交阈值（如果存在）的工具的效用，在任何谱系管理的人群中。