How did the Guam Rail come back from extinction in the wild?
After more than 30 years, the Guam Rail is back: breeding naturally beyond the confines of captive breeding enclosures – making it only the second bird species ever to recover from extinction in the wild. How did conservationists do it, and what can we learn about the threat of introduced predators?
A circle of people stepped in towards a few unwilling flightless birds, as they darted about on a patch of US military land on the western Pacific island of Guam in the mid-1980s. The elder generation of Chamarro people knew a thing or two about catching ko’ko’ (the local name for the Guam Rail Hypotaenidia owstoni) as tens of thousands of these fast-running, chocolate-brown birds were once widespread on the island and routinely corralled to be kept for food – so it’s likely these birds were scared to death. This, however, was one of a few compassionate moments of salvation, when an entire species of just 21 birds (including a few eggs) was clutched from the jaws of extinction and taken into captivity.
Had this momentous herding not taken place, then the Guam Rail species would have certainly succumbed to the Brown Tree Snake Boiga irregularis, a voracious non-native predator that can grow three metres long and was introduced to Guam by a US military cargo ship returning from the Solomon Islands shortly after World War II. However, after over thirty years of work by a small team in the Guam Department of Agriculture, including a highly successful captive breeding programme on Guam and in US zoos, the 2019 Red List update proclaimed the Guam Rail as ‘extinct in the wild no more’.
“We’re walking on cloud nine”, said Suzanne Medina, Guam Department of Agriculture. “It’s so neat to hear the world talk about ko’ko’ and the California Condor in the same sentence” – referring to the only other bird in history to recover from the classification Extinct in the Wild. Medina has worked with the Guam Rail for over 20 years, in trial-and-error efforts to make captive breeding and reintroduction work. Among recent negative news about the environmental crisis, success stories like this can seem rarer than endangered species themselves, but now more than ever it is the hope and inspiration gleaned from the dedication of the conservationists behind these successes that must be shared.
In the 1960s Guam was a different place – not only with the ominous buzz of a strategic US military territory during the Vietnam War, but biologically. As this remote 50-by-10 km island became inundated by the flourishing tree snake, Guam’s forests changed forever, falling ever more silent and filling with spiders’ webs as insectivorous birds disappeared. Studies made by stick-wielding ecologists (to clear paths of webs) have shown that the forest is thinning and unable to rejuvenate because of bird loss, as most tree species rely on birds to disperse seeds and improve their chances of germination. Mechanical infrastructure was affected too: before electrical companies found solutions, the island even suffered frequent ‘brown outs’ – power outages attributed to the snakes arcing electrical wires. Today, whilst snake control measures (such as setting traps and air-bombing dead mice laced with a painkiller lethal to the snakes) heavily suppress them in key areas, there are thought to be over two million of these nocturnal predators on the island.
In the 70s and 80s, Guam’s birds were disappearing faster than conservationists could react, but it was hard to prove the declines; a graduate biology student at the time, Julie Savage, was even heckled at a conference for saying that Brown Tree Snakes were the cause. But she was right, and it turned out to be one of the worst cases ever of decimation by an introduced species. With no evolved natural defences against the snake (and the snake having no predators on Guam), twelve bird species were wiped out on Guam by the 1980s, including five species found nowhere else: three of which are now, sadly, globally extinct (including the Guam Flycatcher Myiagra freycineti); plus the Guam Kingfisher Todiramphus cinnamominus (still Extinct in the Wild today but captive-bred), and the Guam Rail. With no time to lose, the rail and kingfisher were put behind snake-proof enclosures on Guam with the aim of urgently bolstering the populations.
The team created “dating profiles” for pairs based on a balance between genetic importance and personality
“If it wasn’t for the zoos stepping up to begin our captive breeding, we would have lost ko’ko’ and sihek [Guam Kingfisher] too”, says Medina. Captive breeding is not easy, especially when little is known about a species, and some species are not able to cope with life behind bars at all. For the rails in the facility on Guam, dubbed ‘the railyard’, it was a steep learning curve. With the stakes high, the team had to adjust quickly when things didn’t go to plan – “learning from the birds”, as Medina puts it.
“On one hand they’re walking dinosaurs, pouncing at a skink, and on the other they can be super curious and playful”, says Medina. The birds became like family to the team – and this was key to their success. They created “dating profiles” for pairs based on a balance between genetic importance and personality, knowing which had “behaviour issues” – like males who needed to be allowed out to “release their aggression three times a day”, or females that were getting tired of breeding (they live longer in captivity and can have up to 36 chicks a year). All of this knowledge was shared with the zoos, and helped lead to a successful increase in the global rail population. “Whenever there was a changeover in staff, there was a big dip in ko’ko’ reproduction”, says Medina – which shows the difference a small group of committed people can make.
Whilst the team have found that adult rails can learn to defend against snakes, and can reproduce in areas of low snake density, Guam is still too dangerous for an unaided wild release. The team initially settled on Rota, a snake-free island north of Guam in the Mariana archipelago, and on a second snake-free site, Cocos – a tiny islet off the south coast of Guam, which saw its first rail release in 2010.
Early attempts to try the birds out in the wild on Rota failed however, with the birds spreading out too far to find each other, or being run over by vehicles. They cried, laughed, and learned on the job, such as when they hiked hours into the forest to release some birds only to later find they preferred nesting in a parking lot; or when an ‘exclosure’ in northern Guam, containing rails that had started foraging successfully on their own, had its snake-proof fence knocked down by a typhoon. But in Medina’s words, they always “keep on keeping on”, taking risks and learning. By 1998 captive breeding was booming, and up to 100 birds were released on Rota per year, with the aim of creating new strongholds.
Today, Rota is home to around 200 Guam Rails, and Cocos to 60-80 (which could soon approach the carrying capacity for the 38-hectare islet). Whilst Guam Rail are no longer extinct in the wild, they are still classified as Critically Endangered, because the population on Rota still requires some active management before the birds are considered fully self-sustaining, and the population size on Cocos is vulnerably small.
Laura Duenas, who has worked with the Guam Rail for a decade and is also researching their genetic diversity, says they’ve now reached a point where there are more birds in the wild than in captivity, and that they keep recording more un-banded rails on Rota – a sure sign of breeding. “In the last five years we’ve also observed a family with chicks about a week old, and I even had two ko’ko’ copulate in front of me during a survey this year!” Duenas also monitors nests on Cocos, which she hopes will be a source population for future releases, meaning they won’t need to be dependent on captive breeding to create sustainable populations on Guam.
“The recovery of the Guam Rail is fantastic proof of how effective targeted conservation action can be,” says Dr Ian Burfield, BirdLife’s Global Science Coordinator (Species). “However, it is important to remember that not all species can be brought back from the brink, especially if their natural habitat has been destroyed. The priority should always be conserving habitats to prevent declines and extinctions from happening in the first place.” For the rail to return to mainland Guam, the brown tree snake would need to be heavily suppressed or removed completely. Only then could Guam’s forests recover.
The Guam Rail is, however, a shining light for captive breeding programmes and for the personal dedication of conservationists. This dedication will continue as Duenas, Medina and colleagues will again construct large exclosures to reintroduce rails to Guam, and also turn their expertise to getting the Guam Kingfisher out of cages. “The birds are good for the forest”, says Medina – this is true for many Pacific island ecosystems, where introduced and invasive species upset the web of life. Looking to the future, Medina says she draws her inspiration from bold, large-scale island restoration projects such as New Zealand’s campaign to be ‘Predator free by 2050’ and BirdLife’s ambitions in the Marquesas and wider Pacific.