A candidate species is a species for which the U.S. Fish and Wildlife Service (Service) has enough information on biological vulnerability and threats to warrant listing as endangered or threatened under the Endangered Species Act (ESA), but we are precluded from doing so by higher priority work within the Listing and Classification Program

Candidate species may be identified on our own initiative through the candidate conservation assessment process, or in response to a petition we have received.

ESA Petitions

Any member of the public may petition the Service to list a species, subspecies, or a population of a species as endangered or threatened under the ESA. During our review of the petition, we may determine that listing the species under the ESA is warranted but precluded. In this case the species is added to the candidate list and their status is annually reviewed.

Learn about the petition process.

The Candidate Assessment Process

Through the candidate assessment process, we assess the status of species that may be declining and identify those for which the best scientific and commercial data available indicates that a proposal for listing is appropriate, based on the following factors:

  • the present or threatened destruction, modification, or curtailment of the species' habitat or range;
  • overutilization for commercial, recreational, scientific, or educational purposes;
  • disease or predation;
  • the inadequacy of existing regulatory mechanisms; and,
  • other natural or manmade factors affecting the species' continued existence.

We gather species information from many sources including other federal and state fish and wildlife agencies, local and tribal governments, and academia.  One chief source of information is the network of State Natural Heritage Programs databases, which track species that are already imperiled, and those that are declining or at-risk.  Some of this data is available through NatureServe Explorer. Recently updated State Wildlife Action Plans also provide information on species of greatest conservation concern to states and territories. 

When sufficient information is developed to make a well-documented, biologically sound determination about a species’ conservation status, our field office biologists consider whether it meets the criteria for listing under the ESA. Our regional offices then provide recommendations for additions to the candidate list to the Service Director, who makes the final decision on whether the species is added to the list of candidates.

Candidate species are assigned a listing priority number based on the magnitude and immediacy of threats they face, as well as their taxonomic uniqueness. This number is a key factor in our decisions to proceed with a formal proposal to list a species (see 1983 published guidance on listing priority numbers). Listing priority numbers range from one to 12. A species with a listing priority of one has the highest priority for listing.

Identification of candidate species and the factors influencing their status, and the assignment of listing priority numbers, assists us and our partners in identifying and prioritizing conservation efforts that are most likely to be effective in addressing threats and removing the need for listing. 

Annual Status Reviews

Each year, we consider the best available scientific and commercial data, and reassess the threats to species previously identified as candidates. These analyses, published annually in the Candidate Notice of Review, allow a species’ status to be updated until a proposal to list the species as endangered or threatened can be completed, or new information indicates that the species no longer needs protection under the ESA. 

Decisions to elevate or remove species from candidate status, or update listing priority numbers, requires careful analysis and documentation of the best available scientific information regarding a species and factors influencing its status, as well as the known effects of ongoing conservation efforts.

We evaluate how conservation efforts have removed or reduced threats to the species. At the time we make our decision on whether to elevate a species to candidate status, or remove a species from candidate status, some of these conservation efforts may have been planned but not yet implemented, or have been implemented but not yet demonstrated whether they are effective in reducing or removing threats to a species. We assess some efforts according to our Policy for the Evaluation of Conservation Efforts When Making Listing Decisions – a joint policy with the National Marine Fisheries Service (NMFS). The policy was developed to provide a set of consistent standards for evaluating individual conservation efforts to identify those for which there is a high level of certainty of implementation and effectiveness in removing threats to a species.

View the current list of candidate species.


Butterfly with orange, brown, and white wings perched perched on a flower head gathering nectar with another butterfly on the backside of the flower head.
We assess the conservation status of species, using the best scientific information available, and identify those that warrant listing as endangered or threatened under the Endangered Species Act. A species that we find warrants a proposal to list as endangered or threatened, but listing is...
Close up of a California condor. Its pink featherless head contrasts with its black feathers.
We provide national leadership in the recovery and conservation of our nation's imperiled plant and animal species, working with experts in the scientific community to identify species on the verge of extinction and to build the road to recovery to bring them back. We work with a range of public...