In general, it is illegal to kill an animal that is on the endangered species list. In the United States, the Endangered Species Act (ESA) protects species that are considered to be in danger of extinction. The ESA makes it illegal to "take" any endangered species, which includes killing, harming, or harassing the animal. There are some exceptions to this rule, such as when the animal is killed in self-defense or for scientific research. However, these exceptions are narrowly interpreted and must be specifically authorized by the government.
In other countries, the laws protecting endangered species may vary. Some countries have laws that are similar to the ESA, while others may have less stringent laws or no laws at all. It is important to research the laws in your specific jurisdiction before taking any action that could potentially harm an endangered species.