Hidden impacts of conservation management on fertility of the critically endangered kākāpō

Abstract

Background Animal conservation often requires intensive management actions to improve reproductive output, yet any adverse effects of these may not be immediately apparent, particularly in threatened species with small populations and long lifespans. Hand-rearing is an example of a conservation management strategy which, while boosting populations, can cause long-term demographic and behavioural problems. It is used in the recovery of the critically endangered kākāpō (Strigops habroptilus), a flightless parrot endemic to New Zealand, to improve the slow population growth that is due to infrequent breeding, low fertility and low hatching success. Methods We applied Bayesian mixed models to examine whether hand-rearing and other factors were associated with clutch fertility in kākāpō. We used projection predictive variable selection to compare the relative contributions to fertility from the parents’ rearing environment, their age and previous copulation experience, the parental kinship, and the number of mates and copulations for each clutch. We also explored how the incidence of repeated copulations and multiple mates varied with kākāpō density. Results The rearing status of the clutch father and the number of mates and copulations of the clutch mother were the dominant factors in predicting fertility. Clutches were less likely to be fertile if the father was hand-reared compared to wild-reared, but there was no similar effect for mothers. Clutches produced by females copulating with different males were more likely to be fertile than those from repeated copulations with one male, which in turn had a higher probability of fertility than those from a single copulation. The likelihood of multiple copulations and mates increased with female:male adult sex ratio, perhaps as a result of mate guarding by females. Parental kinship, copulation experience and age all had negligible associations with clutch fertility. Conclusions These results provide a rare assessment of factors affecting fertility in a wild threatened bird species, with implications for conservation management. The increased fertility due to multiple mates and copulations, combined with the evidence for mate guarding and previous results of kākāpō sperm morphology, suggests that an evolutionary mechanism exists to optimise fertility through sperm competition in kākāpō. The high frequency of clutches produced from single copulations in the contemporary population may therefore represent an unnatural state, perhaps due to too few females. This suggests that opportunity for sperm competition should be maximised by increasing population densities, optimising sex ratios, and using artificial insemination. The lower fertility of hand-reared males may result from behavioural defects due to lack of exposure to conspecifics at critical development stages, as seen in other taxa. This potential negative impact of hand-rearing must be balanced against the short-term benefits it provides.

Capturing species‐wide diversity of the gut microbiota and its relationship with genomic variation in the critically endangered kākāpō

“…Kākāpō age was binned into 10 year categories to compensate for birds of unknown age that were discovered on Rakiura/Stewart Island in the 1970s–1980s. Kākāpō of unknown age comprised 26% of individuals sampled in this study and were assigned a minimum age of 10 years at date of discovery, an age at which kākāpō typically begin breeding (Digby et al, 2023).…”

“…Cloacal swabs were initially collected if fresh faecal material could not be obtained, but the bacterial profiles of swabs were sufficiently dissimilar to those of faecal material that they could not be used as a proxy (Figure S1). (Digby et al, 2023). saline if stored in RNAlater, or with 70% ethanol if directly frozen.…”

The ghost of selection past: evolution and conservation relevance of the kākāpō color polymorphism

“…The kākāpō has experienced a population decline and significant genetic drift over the past 30,000 years (30 KYA), followed by a sharp, anthropogenically induced population bottleneck resulting in just 51 surviving individuals in 1995 7 . Under the close management of the Aotearoa New Zealand Department of Conservation Te Papa Atawhai Kākāpō Recovery Programme in partnership with Ngāi Tahu 4,8 , the population size has increased to 247 birds located on several predator-free islands [as of September 1 st 2023]. Despite these severe bottleneck events, the population exhibits a relatively balanced distribution of green and olive individuals; to understand the evolution of this color polymorphism, we here assess the phenotype's genomic basis and how the genetic polymorphism was first established and has since been maintained in the population.…”