Federal definitions
The Endangered Species Act defines both terms in 16 U.S.C. § 1532:
- Endangered species: “any species which is in danger of extinction throughout all or a significant portion of its range”
- Threatened species: “any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range”
- Species: the term “includes any subspecies of fish or wildlife or plants, and any distinct population segment of any species of vertebrate fish or wildlife which interbreeds when mature”
As Colorado Parks and Wildlife describes it, the act is “administered by the U.S. Fish and Wildlife Service and the Commerce Department’s National Marine Fisheries Service.”
How Colorado Parks and Wildlife describes them
Colorado Parks and Wildlife (CPW) puts the two categories in plain language:
- “Endangered wildlife are species that are likely to become extinct throughout all or a large portion of their range.”
- “Threatened wildlife are species that are likely to become endangered in the near future.”
Colorado’s statutes define the categories in C.R.S. 33-1-102:
- Endangered species: “any species or subspecies of native wildlife whose prospects for survival or recruitment within this state are in jeopardy, as determined by the commission.”
- Threatened species: “any species or subspecies of wildlife which, as determined by the commission, is not in immediate jeopardy of extinction but is vulnerable because it exists in such small numbers or is so extremely restricted throughout all or a significant portion of its range that it may become endangered.”
“The commission” is the Colorado Parks and Wildlife Commission. Under C.R.S. 33-2-105, it is unlawful to take, possess, transport, export, process, sell or offer for sale, or ship state-endangered or state-threatened species, except as otherwise provided in the article.
On every profile on this site, the Colorado badge shows the species’ state status next to its federal one.
Federal and state statuses can differ
A species can have different federal and state statuses. On this site, 5 species are listed by both, at different levels. Two examples:
- Canada Lynx: federally threatened, listed as endangered by Colorado.
- Colorado Pikeminnow: federally endangered, listed as threatened by Colorado.
A species can also be state-listed without a federal listing. The boreal toad is listed as endangered by Colorado and is not federally listed.
The distinction comes up on Colorado’s 2026 ballot: the right to hunt and fish in Amendment 83 would not apply to endangered species. Our explainer covers Amendment 83 and Proposition 137.
Other labels you’ll see on this site
Candidate
The U.S. Fish and Wildlife Service describes a candidate species as “a plant or animal species for which we have sufficient information on biological vulnerability and threats” to list it, but listing “is precluded by higher priority work within the Listing and Classification Program.” Candidate species “receive no statutory protection under the ESA.” USFWS encourages voluntary conservation for them (USFWS Candidate Conservation).
Proposed
From the NOAA Fisheries glossary: “A proposed species is one that is found to warrant listing as either threatened or endangered, or delisting, after completion of a status review and consideration of other protective conservation measures.”
The monarch butterfly is an example. It was proposed as threatened in December 2024 and is not yet listed. The final decision is due by June 6, 2030. Read our monarch news story.
SGCN
SGCN stands for Species of Greatest Conservation Need, from Colorado’s State Wildlife Action Plan. CPW says: “The SGCN list includes the species of animals and plants that most urgently need conservation action.” and “All U.S. states and territories update and publish a SWAP every 10 years.”
Colorado’s 2025 plan evaluated 1,408 species. Of those, 612 need conservation action: 152 tier 1 species, 253 tier 2 species and 207 species of greatest information need. SGCN is a planning list, not a legal protection status.
CO Special Concern
Special Concern is a state category the Colorado Division of Wildlife (now Colorado Parks and Wildlife) developed for nongame wildlife, as described in a 1999 Colorado Natural Heritage Program handbook. A species or subspecies of native wildlife qualifies if it meets any one of these:
- It was “removed from the state threatened or endangered list within the last five years”;
- It is proposed for federal listing or is a federal candidate species, and is not already state listed;
- Best available data show “a downward trend in numbers or distribution lasting at least five years” that may lead to threatened or endangered status;
- It is otherwise determined to be vulnerable in Colorado.
CPW’s current Threatened and Endangered Wildlife page uses the label “State Special Concern” next to species but does not define it. The Colorado Natural Heritage Program lists it the same way: “State status per Colorado Parks & Wildlife: Endangered (SE), Threatened (ST), or State Special Concern (SC).”
On legal protection: Colorado’s take prohibitions in C.R.S. 33-2-105 name endangered and threatened species only, and the statute does not mention special concern. Other wildlife laws, such as hunting and fishing rules, still apply to many of these species.
NatureServe rank
NatureServe ranks come in two kinds. A G rank is global, the status across a species’ whole range. Most species on this site show G ranks:
- G1, Critically Imperiled: “At very high risk of extinction or elimination”
- G2, Imperiled: “At high risk of extinction or elimination”
- G3, Vulnerable: “At moderate risk of extinction or elimination”
- G4, Apparently Secure: “At fairly low risk of extinction or elimination”
- G5, Secure: “At very low risk of extinction or elimination”
- GX, Presumed Extinct: “Not located despite intensive searches and virtually no likelihood of rediscovery.”
An S rank is subnational, the status within one state, here Colorado, assigned by Natural Heritage program scientists. S ranks use the same 1–5 scale for risk within Colorado:
- S1, Critically Imperiled: “At very high risk of extirpation in the jurisdiction”
- S2, Imperiled: “At high risk of extirpation in the jurisdiction”
- S3, Vulnerable: “At moderate risk of extirpation in the jurisdiction”
- S4, Apparently Secure: “At a fairly low risk of extirpation in the jurisdiction”
- S5, Secure: “At very low or no risk of extirpation in the jurisdiction”
SX means presumed extirpated; SH means possibly extirpated (known only from historical records, with some hope of rediscovery).
Reading combined codes
- T: “The status of infraspecific taxa (subspecies or varieties) are indicated by a ‘T-rank’”
- Range rank (e.g., G3G4): “A numeric range rank (e.g., G2G3, G1G3) is used to indicate uncertainty about the exact status”
- NR (as in GNR): “Global rank not yet assessed.”
- Q: “Distinctiveness of this entity as a taxon or ecosystem type at the current level is questionable”
- B (e.g., S3B): “Conservation status refers to the breeding population of the species in the nation or state/province.”
Example: the preble's meadow jumping mouse is ranked G5T2. The G5 is the rank for the species as a whole; the T2 is the rank for its subspecies.
These are scientific assessments, not legal designations.