While scientists have documented countless new animal species since the beginning of the 21st century, many others have gone extinct. Humans are a pervasive contributor to extinction despite groundbreaking research and conservation efforts. Determining how many species we have lost is difficult, with daily estimates varying ranging from two dozen to as many as 150. Here's a look at the species recently declared extinct or extinct in the wild.

1 of 11 Pinta Giant Tortoise Arturo de Frias Marques / Wikimedia Commons / CC BY-SA 3.0 The extinct Pinta giant tortoise's (Chelonoidis abingdonii) last known individual was Lonesome George, an icon of the Galapagos, who died in captivity on June 24, 2012. Since then, an expedition team located some first-generation hybrid tortoises on nearby Volcán Wolf on northern Isabela Island, another of the Galapagos Islands in Ecuador. The use of the tortoises as an onboard food source for 19th-century whalers and deforestation from introduced goats led to the extinction of the species.

2 of 11 Splendid Poison Frog Marcos Guerra / STRI The splendid poison frog (Oophaga speciosa) was declared extinct in 2020 and was last recorded in 1992. Researchers believe the chytrid fungus outbreak of 1996 in their home range of the western Cordillera Central in Panama, near Costa Rica, led to their extinction. Once widely kept as pets, there remains a possibility that living specimens exist in captivity. Unfortunately, none inhabit zoos or research collections.

3 of 11 Spix's Macaw Patrick Pleul / AFP / Getty Images The Spix's macaw (Cyanopsitta spixii), endemic to Brazil, was last seen in the wild in 2016. It was declared extinct in the wild in 2019, but there are currently around 160 of these parrots in captivity. This species had its moment in the spotlight when one named Blu starred in the 2011 animated movie "Rio." Unfortunately, the illegal pet trade served as a significant factor in driving the bird to extinction in the wild, as did habitat loss. Hope for the continuance of the species lies in captive breeding programs that intend to reintroduce the birds to the wild.

4 of 11 Pyrenean ibex Joseph Wolf / Wikimedia Commons / Public Domain The Pyrenean ibex (Capra pyrenaica pyrenaica) is one of two extinct subspecies of the Spanish ibex and was declared extinct in 2000. The species was once numerous and roamed across France and Spain. By the early 1900s, its numbers had fallen to fewer than 100. The last Pyrenean ibex, a female nicknamed Celia, was found dead in northern Spain on Jan. 6, 2000. It was determined that she was killed by a falling tree. Scientists took skin cells from the animal's ear and preserved them in liquid nitrogen, and in 2003 an ibex was cloned, making it the first species to become "unextinct." However, the clone died just seven minutes later due to lung defects. Subsequent efforts have failed to produce another clone, but studies examining the DNA viability continue. What caused the Pyrenean ibex's extinction remains unknown, but some hypotheses include poaching, diseases, and the inability to compete with other species for food.

5 of 11 Bramble Cay Melomys State of Queensland / Wikimedia Commons / CC BY 3.0 AU The Bramble Cay melomys (Melomys rubicola) was declared extinct by the IUCN in May 2015 and by the Australian government four years later in 2019. The last sighting of the melomys occurred in 2009 on the coral island Bramble Cay. The Queensland State government names the extinction the first documented mammal extinction caused by human-made climate change. Loss of habitat, particularly the island's vegetation, occurred due to rising sea levels. Furthermore, the analysis undertaken by the Queensland government scientists indicates that storm surges also led to the drowning of some animals.

6 of 11 Western Black Rhino Jerzy Strzelecki / Wikimedia Commons / CC BY 3.0 The rarest of the black rhino subspecies, the Western black rhino (Diceros bicornis ssp. longipes) was recognized by the IUCN as extinct in 2011. The species was once widespread in central Africa, but the population began a steep decline due to poaching. The rhino was listed as critically endangered in 2008, but a survey of the animal's last remaining habitat in northern Cameroon failed to find any of it or indicators of its presence. No West African black rhinos are known to be held in captivity. The West African black rhino is a subspecies of the black rhino, but all rhinos are in trouble. Some things are looking up for Eastern black rhinos, however. Two babies were born in captivity and then released into the wild in 2012. Their birth brought the population to 702, according to the BBC. The video below, created by WWF's Black Rhino Expansion Project, shows the lengths we need to go to prevent the loss of other species:

7 of 11 Moorean Viviparous Tree Snail Simon J. Tonge / Wikimedia Commons / CC BY 3.0 The Moorean Viviparous Tree Snail (Partula suturalis) was declared extinct in the wild in 2009. This extinction occurred due to a chain of events caused by humans. The African Land Snail was introduced to Tahiti in 1967 as a food source. It escaped and began to destroy crops. Biologists later attempted to control the African Land Snail by introducing the rosy woflsnail to the area starting in 1977. The rosy wolfsnail then eradicated the native snails, including the moorean viviparous tree snail. This and other species of Polynesian tree snails now only exist in captive populations. Reintroductions have shown these snails can breed in the wild, but the rosy wolfsnail population continues to prey upon them.

8 of 11 Po‘ouli Paul E. Baker / USFWS / Wikimedia Commons / Public Domain The po'o-uli (Melamprosops phaeosoma) is endemic to Hawaii's island of Maui and was listed as extinct in 2019. Recorded for the first time by college students participating in the Hana Rainforest project on the southeastern slopes of Haleakala in 1973, this bird ate spiders, insects, and snails. Of the three known birds discovered in 1998, one died in captivity in 2004, and efforts to spot the remaining two have come up empty since that year. Habitat destruction, the rapid spread of disease-carrying mosquitoes, and invasive species are the leading theories behind the extinction.

9 of 11 Baiji Institute of Hydrobiology, Chinese Academy of Sciences / Wikimedia Commons / CC BY-SA 4.0 China's baiji, (Lipotes vexillifer) or Yangtze River dolphin, is listed as critically endangered, possibly extinct. In 2006, scientists from the Baiji Foundation traveled up the Yangtze River for more than 2,000 miles equipped with optical instruments and underwater microphones but were unable to detect any surviving dolphins. The foundation published a report on the expedition and declared the animal functionally extinct, meaning too few potential breeding pairs remained to ensure the species' survival. The last documented sighting was in 2002. In October 2016, a team of amateur conservationists claimed to have seen the creature near the city of Wuhu in China's Anhui province. However, they did not photograph the dolphin and had no other conclusive proof of its existence. The decline in the baiji dolphin population is attributed to a variety of factors including overfishing, boat traffic, habitat loss, pollution, and poaching.

10 of 11 Maui 'Akepa Hiart / Wikimedia Commons / Public Domain The Maui 'akepa (Loxops ochraceus) is a songbird native to Maui listed as presumed extinct in 2018. The last sighting of this bird occurred in 1988. Recent audio recordings provide some hope that a few birds may yet survive. Like other Hawaiian forest birds, habitat loss, competition from introduced species, and death due to disease led to its disappearance. Researchers blame avian flu spread by introduced mosquitos for the extinction of the Maui 'Akepa.