Ranks represent a prioritization scheme used by the network of Natural Heritage Programs and Conservation Data Centers to determine the conservation status of a species. The rank is primarily based upon the number of known occurrences but other factors such as habitat quality, estimated population size and trend, range of distribution, and threats to species or habitat are also considered. See Master (1991) for a detailed review and evaluation of this ranking system. The global rank denotes the rank of the species throughout its range, whereas the state rank refers to the species status within the borders of Idaho. Both the global and state ranks are subject to periodic revision as new information is obtained on a species either in Idaho or elsewhere in its range.
1 - Critically imperiled because of extreme rarity or because of some factor of its biology making it especially vulnuerable to extinction (typically 5 or fewer occurrences).
2 - Imperiled because of rarity or because of other factors demonstrably making it vulnerable to extinction (typically 6- 20 occurrences).
3 - Vulnerable (typically 21- 100 occurrences).
4 - Not rare, and apparently secure, but with cause for long- term concern.
5 - Demonstrably widespread, abundant, and secure.
E - Exotic or introduced species.
NTMB - Neotropical Migratory Landbird. As defined by Saab and Groves (1992), these are bird species that breed in Idaho and winter in tropical America between the tropics of Cancer and Capricorn. In the atlas, state ranks for these species include the acronym "NTMB."
Additional information on state and federal classfication of rarity for Idaho animals (e. g., Endangered, Sensitive, etc.) can be found in Idaho Conservation Data Center (1994).