Assessing the impacts of invasive predators on the demography and distribution of native species is critical for understanding mechanisms of species persistence and informing the design of recovery programmes. On the oceanic island of Guam, the introduction of the predatory brown treesnake Boiga irregularis after World War II caused the near-total loss of the native forest avifauna. Localised snake control measures have been implemented since the early 1990s, yet it remains poorly understood how they have impacted Guam’s remaining native bird populations. To address this question, we combined intensive area searches of Andersen Air Force Base (AAFB) with island-wide transect surveys and opportunistic sightings to provide a comprehensive update on the distribution and abundance of Såli (Micronesian Starling, Aplonis opaca) – one of Guam’s last extant native bird species. Area searches of AAFB, where the largest remnant of the Såli population persists, revealed a 15-fold population increase since the last survey in the early 1990s, and transect surveys and opportunistic sightings indicate incipient recolonisation of other urbanised areas of northern and central Guam. We estimate the current island-wide population size at ~1,400 individuals. The population increase can likely be attributed to a combination of snake control measures and the Såli’s ability to exploit urban refugia for nesting and roosting. Although these trends demonstrate some population recovery, a skewed age ratio (>90% adults and subadults) at AAFB and a highly urbanised distribution and low abundance outside AAFB indicate that snake predation continues to strongly impact the population. More intensive snake suppression efforts, particularly in forested areas, may allow for the Såli population to attain its former distribution and abundance on Guam. More broadly, our findings reinforce the importance of urban areas as refugia for some threatened species.

评估入侵性捕食者对本地物种人口和分布的影响对于了解物种持续存在的机制和为恢复计划的设计提供信息至关重要。在海洋岛屿关岛，二战后掠食性棕色树蛇 Boigaregularis 的引入导致原生森林鸟类几乎全部消失。自 1990 年代初以来，已实施了局部蛇类控制措施，但人们对它们如何影响关岛剩余的本地鸟类种群仍然知之甚少。为了解决这个问题，我们将安徒生空军基地 (AAFB) 的密集区域搜索与全岛横断面调查和机会性目击相结合，以提供有关 Såli（密克罗尼西亚椋鸟，无花果) – 关岛现存最后的本土鸟类之一。对 AAFB 进行的区域搜索显示，自 1990 年代初的最后一次调查以来，人口增长了 15 倍，横断面调查和机会主义目击表明关岛北部和中部其他城市化地区的重新殖民化初期。我们估计目前全岛人口规模约为 1,400 人。人口增长可能归因于蛇控制措施和萨利人利用城市避难所筑巢和栖息的能力。尽管这些趋势表明种群数量有所恢复，但 AAFB 的年龄比例偏差（>90% 成人和亚成人）以及高度城市化的分布和 AAFB 以外的低丰度表明蛇捕食继续对种群产生强烈影响。更密集的蛇类抑制工作，特别是在森林地区，可能会使 Såli 人口达到其在关岛以前的分布和丰富程度。更广泛地说，我们的研究结果强化了城市地区作为某些受威胁物种避难所的重要性。