Extinct Bird Provides Roadmap For Reintroducing Other Long-Lost Animals

The Guam kingfisher has been extinct in the wild for more than 30 years but thanks to intense conservation efforts, it now stands on the brink of being released back into the wild

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NOTE: Originally published under the title: “Extinct Guam Kingfisher Provides Blueprint For Reintroducing Other Long-Lost Animals”

Adult male sihek, or Guam kingfisher (Todiramphus cinnamominus). This critically endangered species is extinct in the wild. (Credit: John Ewen)

The Guam kingfisher, or ‘sihek’ as it’s known by the Chamorros, the indigenous people living on Guam, is becoming a symbol of conservation hope these days. It has been extinct in the wild for more than 30 years, but thanks to intensive captive breeding and conservation efforts, it now stands on the brink of being released back into the wild.

The sihek, Todiramphus cinnamominus, is a compact rusty-red bird with a long dark blue tail and short dark blue wings, a large charcoal grey bill and a black stripe through its eyes. This handsome bird was endemic to the small tropical island of Guam, which is a territory of the United States located in the western Pacific Ocean. They were reported to be ‘common’ in 1945, but declined rapidly until the last wild sihek was spotted in 1988. Why did they suddenly disappear?

Brown tree snake (Boiga irregularis) is an invasive species on Guam, where it wiped out nearly all the endemic birds and other vertebrates on the island. (Credit: Gordon H. Rodda / USFWS / public domain)

By way of the US military, the brown tree snake, Boiga irregularis, was introduced to Guam during World War II. This invasive snake, a notoriously voracious predator, quickly gobbled up all the birds on the island until nine of Guam’s eleven endemic bird species were extinct. The sihek was one of two endemic birds that somehow managed to hold on, although it teetered precariously on the brink of extinction. Fortunately, the last 29 wild sihek were captured and placed into captive breeding programs on the US mainland. Unfortunately, only 16 of these rescued birds would end up successfully breeding in captivity.

Such a tiny founder population has led to a number of problems stemming from the effects of inbreeding depression.

Are captive-bred sihek impacted by inbreeding depression?

A team of scientists led by conservation biologist Amanda Trask, a Postdoctoral Research Associate at the Zoological Society of London (ZSL), investigated whether inbreeding depression was impacting sihek survival and reproductive success or if there something else associated with decades in captivity might be impacting their health.

Dr Trask specializes in population ecology and genetics, and her current research uses population modelling to evaluate the potential outcomes of different conservation management scenarios. Dr Trask’s ultimate goal is to develop a conservation translocation plan to reintroduce Guam kingfishers back into the wild.

“I have a background in conservation biology and population genetics, so I enjoy working with small populations of highly threatened species and there is a great team of people on the sihek project,” Dr Trask said in email.

The rescued sihek population started out with a mere handful of individuals, and the captive population of these birds still remains very small, with roughly 135 individuals alive today. Thus, the resulting sihek population is the product of inbreeding closely-related individuals, which is plagued by problems stemming from in inbreeding depression. Inbreeding depression reduces the overall genetic diversity of a population and reduces the reproductive success and long-term health and survival of individuals, which strongly impacts a population’s long-term viability and overall extinction risk.

In this study, Dr Trask and her collaborators started by establishing that inbreeding depression was having a substantial impact on the lifespan of adult birds as well as their reproductive success: individuals with more inbreeding lived shorter lives and raised fewer chicks than did less inbred individuals. But they were surprised to find that juvenile survival rates were unaffected.

Measuring the sihek’s extinction risk

Dr Trask and her collaborators wanted to know how the impacts of inbreeding depression might affect whether the captive population was capable of supporting the release of some individuals into the wild without driving the entire captive population into extinction. To get at this question, they created a statistical model to simulate a variety of potential management scenarios, particularly with the goal of removing some birds for wild releases (‘harvesting’).

F I G U R E 3 : Simulated size of the sihek ex-situ population under alternative management scenarios. Solid lines indicate mean population size across model iterations, with standard deviation (shaded areas). Colours indicate model scenarios including our sihek B estimates (red), no inbreeding depression (blue), or default B (black). (doi:10.1038/s41598–020–79979–4)

If the current sihek population management scenario remains unchanged, Dr Trask and her collaborators’ model predicted sihek would rapidly decline in the future, and removing individuals for release into the wild would only accelerate this rate of decline (Figure 3, upper two panels).

However, if captive sihek were encouraged to produce more chicks, the population would increase, despite the negative impacts of inbreeding depression (Figure 3, lower left panel). Furthermore — and most important — this growing population would be able to support the removal of some individuals for release into the wild without harming the captive population’s long-term viability (Figure 3, lower right panel).

This was good news indeed.

Dr Trask and her collaborators’ findings highlight the urgent need to work on increasing the captive population of sihek to avoid future extinction as well as to support sustainable wild releases of some individuals.

This finding — increase the population size, even if they are inbred — makes intuitive sense, which raises the question: if zoos and other captive breeding institutions actually can breed more sihek, why haven’t they done so?

Sihek are expensive to maintain in captivity

“This is quite a tricky question in reality, because we are constrained by how much space there is in the zoos and breeding institutions to keep them,” Dr Trask explained in email. “[B]ecause they are highly territorial, [each pair] needs their own enclosure and [they] also have a specialized diet (their natural diet is mainly lizards and insects), this makes them expensive to keep in captivity.”

Additionally, the coronavirus situation is making things more difficult for zoos and their ongoing captive-breeding efforts.

“The cost of breeding and housing sihek has been brought into focus further with the Covid-19 pandemic, where lockdowns have meant zoos have had to close, which has put financial strain on zoos,” Dr Trask said in email.

This puts zoos into a very tight situation.

“As an extinct-in-the-wild species, sihek are currently entirely under human care,” Dr Trask said in email, adding: “It is really important that we try to establish wild populations of them as soon as possible, to reduce potential for things like adaptation to captivity, but also so that we can grow the population.”

Can extinct-in-the-wild bird species fly wild and free again?

Another extinct-in-the-wild bird from Guam, the Guam rail, or ko’ko’, Hypotaenidia owstoni, is helping pave the way for the sihek recovery. Ko’ko’ were recently downlisted to Critically Endangered after 16 captive-bred birds were released onto the uninhabited and snake-free Cocos Island in 2010, followed by release of another 12 individuals in 2012. This species is flightless, so it is an easy target for the brown tree snake, which would have quickly eaten it into extinction if not for several quick-thinking conservation-minded people who rescued the last individuals of this species.

In 2019, ko’ko’ made conservation history by becoming the second bird species to ever be downlisted by the International Union for Conservation of Nature (IUCN) from extinct-in-the-wild to Critically Endangered (the California condor was the first).

The recent reclassification of the ko’ko’ from extinct-in-the-wild to Critically Endangered shows there is precedent for recovering extinct island species.

“I think it would be amazing if the sihek could follow its fellow Guam endemic’s path.”

Critically endangered Guam rail, or ko’ko’ (Hypotaenidia owstoni), at the Cincinnati Zoo. (Credit: Greg Hume / CC BY-SA 3.0)

Dr Trask and her collaborators now have a clear course of conservation action for helping sihek, so they are hopeful.

“We are trying to recruit more partners to the SSP [ Species Survival Plan], so that we can expand the population,” Dr Trask elaborated in email. “[I]f releases are successful, then the learning sites themselves could create extra space to grow the population, so that we then have birds available for releases to larger establishment sites.”

A Sihek Recovery Team, comprised of experts, researchers and conservation practitioners from ZSL, Calgary Zoo, US Fish & Wildlife Service, Guam Division of Aquatic and Wildlife Resources, and Association of Zoos and Aquaria, are working with other stakeholder groups to create a recovery plan for the sihek (PDF). Not only will this plan involve increased sihek breeding to grow the captive population, but it also will involve conservation translocations for small numbers of sihek to be released into the wild.

“For first small, trial releases of sihek to the wild, we have been looking at Cocos island, which is a small islet off Guam, and Palmyra atoll in the Northern Line Islands,” Dr Trask said in email. “Cocos island was free of snakes and still has some of the herpetofauna that have been extirpated from Guam and is also a reintroduction site for the ko’ko’ (Guam rail). However, there has recently been a brown tree snake incursion on the island, so efforts are now under way to eradicate the snakes there and we are waiting to see what the outcome of that is before any sihek releases there.”

The Palmyra Atoll may be a release site for captive-bred sihek, or Guam kingfishers (Todiramphus cinnamominus). (Credit: USGS Unmanned Aircraft Systems / CC BY 2.0)

Palmyra atoll is free of brown tree snakes, so Dr Trask and her team are planning sihek releases there in collaboration with the US Fish and Wildlife Service and The Nature Conservancy.

They are also planning future releases of sihek onto Guam, too, despite the presence of brown tree snakes there.

“For releases to sites where a larger population can be established, we are considering snake-proof fenced areas on Guam (but I agree that brown tree snakes are a formidable bird predator, so there would need to be on-going efforts to suppress the snake population and maintain snake-proof fencing),” Dr Trask said in email. “[W]e are also considering assisted colonisations to other nearby Micronesian islands without brown tree snakes.”

This planning process involves multiple stakeholder groups, including native Chamorro people and local community groups, with the goal of working out where are the best possible locations for sihek releases.

“If successful, these releases will be the first sihek in the wild for over 30 years!”


A. E. Trask, G. M. Ferrie, J. Wang, S. Newland, S. Canessa, A. Moehrenschlager, M. Laut, L. Barnhart Duenas & J. G. Ewen (2021). Multiple life-stage inbreeding depression impacts demography and extinction risk in an extinct-in-the-wild species, Scientific Reports, 11:682 | doi:10.1038/s41598–020–79979–4

Originally published at Forbes.com on 25 February 2021.

PhD evolutionary ecology/ornithology. Psittacophile. scicomm Forbes, previously Guardian. always Ravenclaw. discarded scientist & writer, now an angry house elf

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