Knowing about a threatened species’ effective population size (N_e) is vital to assess population trends and guide conservation efforts. Highly mobile and migratory species are some of the most threatened yet hardest to monitor groups. Recently, a conversion has been proposed to convert estimates of the effective number of breeders (N_b) to N_e using two life history traits. We evaluated current methods to estimate N_b and N_e to inform conservation management using the black-fronted tern/tarapirohe (Chlidonias albostriatus) as a case study. Black-fronted terns are endangered, highly mobile and traditional monitoring methods have proven difficult. Based on 17 microsatellites and extensive sampling throughout the breeding range, we estimated mean N_b ca. 700 based on sibship assignment and linkage disequilibrium (LD) methods. Mean estimates of LD N_e based on the conversion of N_b and two life history traits was 668, while LD N_e based on samples of chicks and adults was 3216. The low ratio of N_b/N_e when using the N_e estimate based on mixed-age samples is probably driven by a combination of N_b being more sensitive to the large recruitment failure of individuals, large variation compared to mean reproductive success between same-age and same-sex individuals, and the ongoing overall population decline. We highlight that in relatively long-lived and threatened species, a combination of N_band N_e estimates are more appropriate to assess the population status rather than solely relying on N_eof mixed-age samples. For black-fronted terns, we recommend increased conservation management and genetic monitoring based on N_b and N_e.

了解受威胁物种的有效种群数量（N _e）对于评估种群趋势和指导保护工作至关重要。高度流动和迁徙的物种是最受威胁但最难监测的群体。最近，已经提出了一种转换，以使用两个生活史特征将育种者的有效数量（N _b）的估计值转换为N _e。我们评估目前的方法来估算ñ _b和ñ _Ë使用通知养护管理黑额燕鸥/ tarapirohe（Chlidonias albostriatus）作为案例研究。黑面燕鸥濒临灭绝，机动性强，传统的监测方法被证明是困难的。根据17个微并在整个繁殖范围广泛的取样，我们估计平均Ñ _b约 700基于同伴关系分配和链接不平衡（LD）方法。的LD平均数估计Ñ _Ë基于转化Ñ _b和两个生活史是668，而LD Ñ _Ë基于小鸡的样品和成人是3216的低比Ñ _b / Ñ _Ë使用时Ñ _Ë估计基于混合年龄的样本可能是由以下因素共同驱动的ñ _b是个人的招聘大失败，大的变化相比，平均同年龄和同性别的个体，以及正在进行的总人口下降的繁殖成功率更敏感。我们着重指出，在相对长寿和受威胁的物种中，N _b和N _e估计值的结合更适合评估种群状况，而不是仅仅依赖混合年龄样本的N _e。对于黑额燕鸥，我们建议基于N _b和N _e加强保护管理和基因监测。