After months of jungle exploration, Gibson Morib was exhausted and his body was on the brink of collapse. Whilst he was deep in sleep, the ringtone of his mobile phone suddenly sounded, a notification popped up, displaying a blurry photo of a fuzzy, long-beaked animal. This unexpected image prompted Morib to rush out of his room, mount his motorcycle, and race to a field research station in the Sentani region of New Guinea, Indonesia. There, he witnessed a scene that moved him to tears: traversing the remote Cyclops mountains, even with an eye that had suffered leech attacks, his team finally captured an image of the rare Attenborough's long-beaked echidna, the first recorded sighting of the species in over 60 years. Morib, a biologist at the University of Paradise Birds in Indonesia, excitedly expressed, "I am so overwhelmed right now, I can only be grateful for God's mercy."

For the scientific community, declaring a species to be completely extinct is a heartbreaking matter. Therefore, researchers sometimes mark a species as "temporarily missing" after it has not been observed for over a decade, holding on to hope that they might be rediscovered in the future. It is this enduring hope that led to the rediscovery of several species believed to have been lost in 2023, such as South Africa's Van Zyl's Golden Mole and Australia's Grassland Earless Dragon.

Recently, the journal "Global Change Biology" published a study completed by an international research team. They shared various scientific methods for finding "lost" species of mammals, amphibians, reptiles, and birds. Conservation biologist Thomas Evans of the Free University of Berlin, with the assistance of researchers from countries such as China, the USA, Ecuador, and South Africa, spent two years compiling a very detailed catalogue of "missing" tetrapods, which not only recorded those species that still have not been seen, but also those that have been rediscovered.

The inspiration for Evans to participate in this project came from Julian P. Hume's book "Extinct Birds". Although the book records profound sadness, its appendix offers a glimmer of hope, listing species that were once mistakenly thought to be extinct but were unexpectedly found again. The catalogue compiled by Evans and his colleagues indicates that there are currently up to 856 species that are still missing. Despite technological advances, with methods such as environmental DNA, sound recognition software, and even indirect confirmation of an animal's presence by analyzing microorganisms remaining in its stomach, the pace of field expeditions discovering new species is far slower than the rate of species loss.

Recent scientific analyses have revealed a troubling fact: among the species that have disappeared, about a quarter are very likely to have been permanently lost from the Earth. In particular, larger-sized animals with conspicuous appearances, such as mammals and birds that once lived in densely populated areas and near economically developed countries, have so far not been observed again. The thylacine is a notable case; this marsupial that resembled a wolf has not been found since the last one died in a zoo at the end of 1936, despite decades of search efforts by scientists.

Experts point out that this dilemma strongly suggests that the thylacine may already be extinct. Besides the thylacine, over two hundred animal species identified as missing have been thoroughly searched for, but similarly, there has been no trace of them. However, those species that are not easily rediscovered, particularly reptiles, may still survive, as they are usually harder to find, and fewer people are looking for them. These less noticeable small species have a greater possibility of survival. In fact, in the past decade, the number of rediscoveries of small reptiles, once thought to be lost, has increased rapidly, doubling the amount from the previous decade.

The research also indicates that mammals on islands are more likely to face extinction than their counterparts living in other environments. As for birds, the study finds that they are most likely to be rediscovered 66 years after they are thought to have disappeared, a duration sufficient to inspire searches without leading to despair of their complete extinction.

In conservation efforts, wildlife protectors like Christina Biggs might gain help from these research details. Since 2017, Biggs has been compiling a list of species they hope to rediscover for the conservation charity "Return to the Wild", and the limited resources present her with a difficult choice when deciding how to allocate funds. The findings from this list will help the organization update the search list for the upcoming year 2024.

However, rediscovery is not always beneficial to the species that were once lost. After a species is found, conservation action may need to be taken quickly to fend off poachers and tourists within a matter of months. The rediscovery of the Attenborough's long-beaked echidna is one such case, where the discoverer has not revealed the exact location to prevent exposure to hunters or others who could pose a threat.

The ecologist involved in the discovery of the echidna cautions that publicizing a rediscovered species is not just about spreading knowledge to the world, but can also mean exposing the animals to hunters. On the other hand, the naming of these species in local languages often relates to their value or characteristics, such as in the local Papuan Tabla dialect, "amokalo" is a name for echidnas that includes the meaning of "fat", proving their popularity as a tasty treat in the area. Biggs also emphasizes that rediscovering species is very likely to boost interest and actions in species conservation.

"Once a species has been rediscovered, it can enter the process of creating protected areas," she says. "All the hard work we do can potentially save other species in the same habitat. To me, this is full of hope."

For example, in 2015, someone in Brazil heard the call of the Blue-eyed Ground Dove (Columbina cyanopis) for the first time in 75 years. This discovery led to the establishment of a state-level conservation park spanning 3.6 million acres. The disappearance of each species is not only an ecological loss but also a cultural one. Among the Yunsusapari tribe near the Cyclops Mountains, the echidna (a small mammal) was once used as a peaceful means of settling disputes.

Moribiti mentioned: "If brothers or friends have conflicts, they must find a thorn to settle their disputes." However, with the scarcity of species, this method of peacefully resolving conflicts has become increasingly difficult to sustain.

"Everything is interconnected, and every species is important. They play unique roles in the ecosystem and achieve their own goals, all of which together support the thriving of all life on Earth." Biggs said so.