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

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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.