A unique opportunity to study fertility and maternal investment in the critically endangered kakapo (Strigops habroptilus)

鸮鹦鹉（学名Strigops habroptilus）是一种极度濒危的不会飞的鹦鹉，原产于新西兰。目前世界上只有147只鸮鹦鹉，全部由新西兰自然保护部的鸮鹦鹉恢复小组在没有捕食者的近海岛屿上管理。管理鸮鹦鹉种群的恢复是具有挑战性的：鸮鹦鹉只有在条件良好的情况下繁殖，而当它们繁殖时，大约70%的蛋无法孵化。在这些未孵化的卵中，大约75%的卵看起来是“不育的”——也就是说，它们没有发育的迹象。然而，卵子发育不全的原因可能是：(i)受精失败，这可能是由于精子不足或质量差造成的；或（ii）胚胎早期死亡，这可能与女性状况不佳、近亲繁殖或环境有关。区分未受精卵和早期胚胎死亡的卵子是很困难的，但我们之前已经建立了这样做的方法，使我们能够识别和减轻孵化失败的潜在原因。鸮鹦鹉的繁殖是高度不可预测的，它依赖于几种果实周期不规则的树种的丰富食物。鸮鹦鹉的繁殖季节平均每2-4年发生一次，通常只有不到50%的雌性产卵。在过去的20年里，只有三个主要的繁殖季节，大多数雌性都试图繁殖。今年（2019年），特殊的生态条件导致了创纪录的繁殖率，超过90%的雌性在繁殖季节预计开始之前就产卵了。鸮鹦鹉恢复小组最近报告了有记录以来的第一次5个蛋的窝，预计在这个季节晚些时候会有前所未有的第二轮筑巢。到目前为止，鸮鹦鹉的小种群规模和缓慢的繁殖速度限制了我们对其生殖生物学的了解，但这个季节的极端不寻常的情况提供了一个千载难逢的机会，可以获得所需的样本量，以解决这种极度濒危鸟类繁殖失败的关键问题。我们提出的研究将分析这个季节生产的所有未孵化的鸮鹦鹉蛋，使用我们自己建立的方法来确定孵化失败是由于受精失败还是早期胚胎死亡。我们将量化到达卵子的精子数量，以评估受精失败是否由精子缺乏引起，并确定胚胎死亡的发育阶段，目的是将其与外部原因联系起来。最后，我们将通过记录鸮鹦鹉产卵的数量、大小和时间来量化雌性鸮鹦鹉在生殖行为和投资方面的差异，并收集雌性鸮鹦鹉如何照顾后代的数据。然后，我们将评估这些特征与生育能力、胚胎存活、小鸡发育以及其他因素（如年龄、状况和生殖史）的关系，这些数据可从鸮鹦鹉恢复小组的长期监测中获得。这项工作对于规划这一标志性物种的未来管理至关重要，并将大大提高我们对鸟类生殖问题的更广泛理解。

The kakapo (Strigops habroptilus) is a critically endangered flightless parrot native to New Zealand. Only 147 currently exist in the world, all managed on predator-free offshore islands by the New Zealand Department of Conservation's Kakapo Recovery Team. Managing the recovery of the population is challenging: kakapo only breed when conditions are good, and when they do, approximately 70% of their eggs fail to hatch. Of these unhatched eggs around 75% appear to be 'infertile' - that is, they show no sign of development. However, undeveloped eggs can result either from (i) fertilisation failure, potentially caused by insufficient or poor quality sperm, or (ii) early embryo death, which may be linked to poor female condition, inbreeding, or the environment. It is difficult to distinguish unfertilised eggs from those that have suffered early embryo death, but we have previously established methods for doing this, allowing us to identify and mitigate the underlying causes of hatching failure.Kakapo breeding is highly unpredictable, being dependent on abundant food from several tree species with irregular fruiting cycles. Kakapo breeding seasons occur on average every 2-4 years and fewer than 50% of females typically lay eggs. There have been only three major breeding seasons - where the majority of females attempted to breed - in the last 20 years. This year (2019), exceptional ecological conditions have induced record-breaking reproductive rates, with over 90% of females laying eggs before the breeding season was even predicted to start. The Kakapo Recovery Team recently reported the first 5-egg clutch on record, and an unprecedented second round of nesting is expected later in the season. Until now, the kakapo's small population size and slow reproductive rate has limited our understanding of its reproductive biology, but this season's extremely unusual circumstances provide a once-in-a-generation opportunity to obtain the sample sizes required to address crucial questions about the causes of reproductive failure in this critically endangered bird.Our proposed research will analyse all unhatched kakapo eggs produced this season, using our own established methods for determining whether hatching failure is due to fertilisation failure or early embryo mortality. We will quantify the number of sperm that reach ova to assess whether fertilisation failure is caused by a lack of sperm, and identify the developmental stage at which embryos die, with the aim of linking this to external causes. Finally, we will quantify how kakapo females differ in reproductive behaviour and investment by recording the number, size, and timing of eggs laid, and collecting data on how females care for their offspring. We will then assess how these traits are related to fertility, embryo survival, chick development, and other factors such as age, condition, and reproductive history, for which data are available from long-term monitoring by the Kakapo Recovery Team. This work will be crucial for planning the future management of this iconic species, and will substantially improve our broader understanding of reproductive problems in birds.