A major myna problem; invasive predator removal benefits female survival and population growth of a translocated island endemic

Invasive predators are a major driver of extinctions and continue to
threaten native populations worldwide. Island eradications of (mostly
mammalian) invasive predators have facilitated the reestablishment of
numerous island-endemic populations. Other invasive taxa, such as some
predatory birds, could pose a more persistent threat due to their ability
to fly and actively re-invade even remote and isolated islands. However,
the impact of invasive predatory birds has been largely overlooked. We
report on a novel sex-specific impact of an invasive-nest predator, the
common myna (Acridotheres tristis), on a reintroduced population of
Seychelles warblers (Acrocephalus sechellensis); translocated from Cousin
Island to Denis Island in 2004. Regular post-translocation monitoring
revealed that female mortality was 20 % higher than males, leading to a
60–70 % male-biased population sex-ratio between 2005 and 2015. This was
attributed to common mynas inflicting severe injuries to incubating female
Seychelles warblers while attempting to prey upon eggs in their nests.
These effects likely contributed to the slower-than-expected population
growth observed (relative to previous translocations of Seychelles
warblers to other islands) over the same period. An eradication programme
beginning in 2011 removed all common mynas from Denis by 2015.
Subsequently, we observed a balancing of sex-specific survival and the
population sex-ratio of Seychelles warblers and, consequently, accelerated
population growth. This study demonstrates the importance of assessing the
threat posed by all invasive taxa (not just mammals) to island
conservation. Furthermore, we show how extended monitoring is needed to
identify problems and develop solutions, post-translocation.

入侵性捕食者是导致物种灭绝的主要因素之一，并持续威胁着全球的本土种群。岛屿上对（主要为哺乳类）入侵性捕食者的清除，促进了众多岛屿特有种群的重建。其他入侵类群，如部分捕食性鸟类，因其具备飞行能力且能主动重新入侵甚至偏远孤立的岛屿，可能构成更持久的威胁。然而，入侵性捕食鸟类的影响在很大程度上被忽视了。我们报告了一种入侵性巢捕食者——家八哥（Acridotheres tristis）对重新引入种群的塞舌尔林莺（Acrocephalus sechellensis）的新型性别特异性影响；该塞舌尔林莺种群于2004年从库金岛（Cousin Island）易地转移（translocation）至丹尼斯岛（Denis Island）。定期的易地转移后监测显示，雌性死亡率比雄性高20%，导致2005至2015年间种群性别比呈现60-70%的雄性偏倚。这归因于家八哥在试图捕食巢中鸟蛋时，对正在孵卵的雌性塞舌尔林莺造成了严重伤害。这些影响可能导致了同期观察到的种群增长慢于预期（相较于此前塞舌尔林莺向其他岛屿的易地转移）。2011年启动的清除计划到2015年已将丹尼斯岛上的所有家八哥清除。随后，我们观察到塞舌尔林莺的性别特异性存活率和种群性别比趋于平衡，进而种群增长加速。本研究表明，评估所有入侵类群（而非仅哺乳类）对岛屿保护构成的威胁具有重要意义。此外，我们还揭示了在易地转移后需要进行长期监测以识别问题并制定解决方案的必要性。