^Appendix 6. Heritage program species ranking definitions. 



Taxa are evaluated and ranked by the Heritage Program on the basis of their global (range-wide) status, and 

 their state-wide status. These ranks are used to determine protection and data collection priorities, and are 

 revised as new information becomes available. 



A scale of 1 (critically imperiled) to 5 (demonstrably secure) is used for these ranks, and each species is 

 assigned the appropriate combination of global and state ranks. 



Example: common loon = G5 / S3 (i.e., species is demonstrably secure globally; in Montana is found within a 

 restricted range). 



Global and state ranks are assigned according to a standardized procedure used by all Natural Heritage 

 Programs, and are defined below. 



Global/state 



Rank Definition (G = Range-wide; S = Montana) 



Gl SI Critically imperiled because of extreme rarity {5 or fewer 



occurrences, or very few remaining individuals), or because of some 

 factor of its biology making it especially vulnerable to extinction. 



G2 S2 Imperiled because of rarity (6 to 20 occurrences) , or because of other 



I factors demonstrably making it very vulnerable to extinction 



throughout its range. 



03 S3 Either very rare and local throughout its range, or found locally 



{even abundantly at some of its locations) in a restricted range, or 

 vulnerable to extinction throughout its range because of other 

 factors; in the range of 21 to 100 occurrences. 



G4 84 Apparently secure, though it may be quite rare in parts of its range, 



especially at the periphery. 



G5 S5 Demonstrably secure, though it may be quite rare in parts of its 



range, especially at the periphery. 



GU SU ' Possibly in peril, but status uncertain; more information needed. 



GH SH Historically known; may be rediscovered. 



GX SX Believed to be extinct; historical records only, continue search. 



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