The United States Fish and Wildlife Service has identified 23 species it says are now extinct. The agency released a list Wednesday that includes 11 birds, eight freshwater mussels, two species of fish, a bat and a plant. Most of the species had been found in states in the southeastern U.S. Eleven species lived in Hawaii or Guam. Perhaps the best known species on the list is the ivory-billed woodpecker. There had been unconfirmed sightings of the bird over the past 20 years. That led to search operations in parts of Arkansas, Louisiana, Mississippi and Florida. But none of the woodpeckers were found. Other species on the list had only been identified in the wild a few times and never seen again. One example is the flat pigtoe, a freshwater mussel found in Alabama and Mississippi. In such cases, the species likely started disappearing shortly after being discovered. In declaring a species extinct, the Fish and Wildlife Service removes it from its Endangered Species Act (ESA). The purpose of the ESA is to call attention to species with the greatest need for protection. The agency said the identifications came after officials carried out “rigorous” investigations based on “the best available science for each of these species.” The declarations will become final after a three-month public comment period. All 23 species were thought to have at least a small chance of survival when added to the ESA list. Only 11 species have been previously removed because of extinction in the nearly half-century since the ESA was signed into law. The Fish and Wildlife Service warned that climate change, combined with other environmental pressures, could make such disappearances more common. As an example, it said nearly 3 billion birds have been lost in North America since 1970. “These extinctions highlight the need to take action to prevent further losses,” the agency said in a statement. Around the world, about 900 species have been documented as extinct. The actual number, however, is thought to be much higher because some are never officially identified. Many scientists have warned that the planet is in an “extinction crisis,” with plants and animals disappearing at 1,000 times the historical rate.