The network of Natural Heritage Programs and Conservation Data Centers--which currently consists of installations in all 50 states, several Canadian provinces, and several Latin American and Carribean countries--ranks the rangewide (GRANK or global rank) and state (SRANK or state rank) status of plants, animals, and plant communities on a scale of 1 to 5. The rank is primarily based on the number of known occurrences, but other factors such as habitat quality, estimated number of individuals, narrowness of range of habitat, trends in populations and habitat, threats to the element, and other factors are also considered. The ranking system is meant to exist alongside national and state rare species lists because these lists often include additional criteria (e.g., recovery potential, depth of knowledge) that go beyond assessing threats to extinction.
Components of Ranks:
G = Global rank indicator; denotes rank based on rangewide status.
T = Trinomial rank indicator; denotes global status of infraspecific taxa.
S = State rank indicator; denotes rank based on status within Idaho.
- 1 = Critically imperiled because of extreme rarity or because some factor of its biology makes it especially vulnerable to extinction (typically 5 or fewer occurrences).
2 = Imperiled because of rarity or because other factors demonstrably make it very vulnerable to extinction (typically 6 to 20 occurrences).
3 = Rare or uncommon but not imperiled (typically 21 to 100 occurrences).
4 = Not rare and apparently secure, but with cause for long-term concern (usually more than 100 occurrences).
5 = Demonstrably widespread, abundant, and secure.
U = Unrankable.
H = Historical occurrence (i.e., formerly part of the native biota; implied expectation that it might be rediscovered or possibly extinct).
X = Presumed extinct or extirpated.
Q = Indicates uncertainty about taxonomic status.
? = Uncertainty exists about the stated rank.
NR = Not ranked.
NA = Conservation status rank is not applicable.
Examples of Use:
- G4T2 = Species is apparently secure rangewide, but this particular subspecies or variety is imperiled.
S2S3= Uncertainty exists whether the species or subspecies should be ranked S2 or S3.
State Ranks Specific to Long Distance Migrants (Bats and Birds):
- A = Accidental (occurring only once or a few times) or casual (occurring more regularly although not every year) in Idaho; a few of these species might have bred on one or more of the occasions when they were recorded.
B = Breeding population.
M = Only applies when migrant occurs in an irregular, transitory, and dispersed manner. Occurrences cannot be defined from year-to-year.
N = Nonbreeding population.
Examples of Use:
- S4N = Fairly common winter resident.
S1B,S5N = Rare breeder but a common winter resident.
S2B,SMN = Rare breeder and uncommon spring and fall transient with lesser numbers remaining as local and irregular (in location) winter residents.