Saving an extinct-in-the-wild species: Genetic threats increase extinction risk of the sihek (Guam kingfisher)

Amanda Trask

Dr Amanda Trask, from ZSL Institute of Zoology, discusses recovery planning for the extinct-in-the-wild sihek or Guam kingfisher and recent research that shows that the sihek faces threats due to inbreeding – the research is published today in Scientific Reports.



Extinction of the sihek in the wild

The sihek (Guam kingfisher, Todiramphus cinnamominus) is endemic to the tropical island of Guam, a United States territory in the Western Pacific Ocean. The accidental introduction of predatory brown tree snakes (Boiga irregularis) to Guam in the 1940’s resulted in rapid population decline and extirpation of the sihek - from being reported as ‘fairly common’ in 1945 to the last sighting of a wild sihek in 1988. Luckily, before their extirpation, 29 wild sihek were captured and translocated to zoos in the US mainland to start a captive breeding program. Sihek have subsequently been maintained in zoos and breeding institutions in the US mainland and Guam, but the population remains at precariously small size, with currently only approximately 135 individuals.

Close up photo a golden brown bird with white belly and black wings, perched on a branch, looking into the camera

Sihek recovery planning

Researchers and conservation practitioners and experts from ZSL, Calgary zoo, US Fish & Wildlife Service, Guam Division of Aquatic and Wildlife Resources, and Association of Zoos and Aquaria have formed a Sihek Recovery Team and are working with other stakeholder groups to create a recovery plan for the sihek. This planning involves consideration of conservation translocations for release of sihek back into the wild.

Genetic threats to the sihek

Due to the small numbers of individuals that were captured from the wild and which successfully bred to establish the captive population, some inbreeding (i.e. mating between related individuals) is inevitable in the sihek population. Inbreeding can reduce individual’s reproductive success and survival (this is called ‘inbreeding depression’), and therefore impact a population’s viability and extinction risk. We therefore investigated levels of inbreeding and any impact on survival and reproductive success in the sihek. We found that inbreeding was having a substantial impact on adult male and female lifespan as well as reproductive success, so that more inbred individuals had reduced lifespans and fewer offspring than more outbred individuals.


Extinction risk

We next wanted to know if our detected impacts of inbreeding depression translated into an effect on the sihek population’s extinction risk and if, when inbreeding depression was taken into account, the population could support removing individuals for release to the wild, without threatening its viability. We therefore created a model of the sihek population to simulate what might happen under different management scenarios, including taking individuals from the captive population for release to the wild.

Our results suggested that, with impacts of inbreeding depression taken into account, the sihek population is predicted to decline rapidly into the future and that removing individuals for release to wild could increase the rate of decline. However, when we simulated a scenario of increasing breeding in the population, the population was predicted to increase in size, even when impacts of inbreeding where taken into account. Under this management scenario, the sihek population was able to support removing individuals for release, without it impacting the population’s viability.

What next for sihek?

The findings from our study highlight the need to increase breeding and grow the sihek population, to ensure the population is viable and can support releases to the wild. Planning is underway for releases of small numbers of individuals to small island ‘learning sites’, where released individuals can be closely monitored – if successful, these releases will be the first sihek in the wild for over 30 years!

© Colton Bolender

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