Wildlife Mitigation Glossary

% Mitigated
The ratio of Current HUs or acres to Lost HUs or acres.

Baseline HUs
Habitat units recorded during the first HEP survey of a Parcel. For land BPA purchases, Baseline HUs are sometimes referred to as "acquisition HUs." As soon as they're available, Baseline HUs replace Minimum Estimated HUs when calculating wildlife credits.

Current HUs
The total number of habitat units available to wildlife species as of the most recent HEP survey; if no Follow-up survey has been conducted, Current HUs = sum of Baseline HUs (in which case Current HUs = Protected HUs); if Follow-up surveys have been conducted, Current HUs = most recent set of Follow-up HUs. a.k.a. "Total HUs".

Degraded HUs
Habitat units lost from degradations to wildlife areas (e.g. wildfires, invasive weed growth, etc). Defined as habitat units reported on follow-up HEP surveys that are less than the baseline HUs.

Enhanced HUs
Habitat units realized from both active (e.g. noxious weed removal, revegatation) and passive (e.g., ceasing to overgraze) habitat improvements to a Wildlife Management Area. Defined as habitat units reported on Follow-up HEP surveys that are greater than the Protected HUs.

Follow-up HUs
Habitat units recorded during the subsequent HEP surveys of a Wildlife Management Area. When calculating Enhanced HUs, only the most recent set of Follow-up HUs (as determined by the most recent HEP survey) are used.

Gained HUs
Habitat units produced by the construction of a federal dam and the inundation behind the dam. Gained HUs were determined by the Impact or Loss Assessment conducted for each federal dam. Gained HUs are often for waterfowl species due to the increase in open-water habitat created by the dam's reservoir.

Habitat Evaluation Procedure
The Habitat Evaluation Procedure (HEP) was developed by the U.S. Fish and Wildlife Service in the late 1970s through the early 1980s and is a species/habitat approach to habitat assessment. Habitat quality for selected "target" wildlife species (as representative of a whole guild of species) is documented with an index, the Habitat Suitability Index (HSI). HSI values range from 0.0 to 1.0, with 1.0 representing optimal habitat conditions for the target species. The HSI values are multiplied by the area (in acres) of available habitat to obtain Habitat Units (HUs) for individual species.

Habitat Unit
Habitat units (HU) are a measurement of the quality of one acre of habitat, as indicated by its suitability for use by target species that typically rely on a particular kind of habitat.

Impact or Loss Assessment
Through the use of the Habitat Evaluation Procedure (HEP), impact assessments, which are also referred to as loss assessments, identify the "habitat units" that were lost and gained due to dam construction and inundation behind the dams.

Lost HUs
Habitat units inundated or lost due to the construction and inundation of a federal dam. Lost HUs were estimated-often decades after the dams were completed-by federal, state, and tribal biologists using the HEP to create an Impact or Loss Assessment for each federal dam.

Minimum Estimated HUs
An intentionally conservative estimate, developed at the time of acquisition, of the number of HUs associated with a Parcel. Minimum Estimated HUs are typically developed using cover type maps and the wildlife managers' familiarity (i.e., "best professional judgment") with the Parcel. After the acquisition, Baseline HUs replace the Minimum Estimated HUs when calculating wildlife credits. If the Parcel is purchased with capital funding, BPA's policy is that the minimum estimated HUs are treated as a minimum level of guaranteed credit. For example, in the unlikely event that the habitat on the Parcel becomes significantly degraded and follow-up surveys indicate that the number of HUs is less than the minimum estimated HUs, BPA must still claim the minimum estimated HUs as the credit associated with the Parcel in order to justify its funding the Parcel by amortizing its costs over time with capital dollars.

Parcel
A tract of land that is acquired or improved through BPA's Wildlife Mitigation Program. Baseline Habitat Evaluation Procedure (HEP) surveys are performed on the parcel immediately after the acquisition or before habitat improvement work begins. Parcels can be aggregated to create a Wildlife Management Area that is managed as a single unit.

Protected HUs
Habitat units realized from the acquisition and holding of Parcels within a Wildlife Management Area. Defined as Baseline HUs less any possible decreases reported on Follow-up HEP surveys (due to degraded habitat as a result of wildfires, invasive weed growth, etc.)

Wildlife Management Area
An area made up of a single parcel or of a collection of parcels that are managed as a single unit. Follow-up HEP surveys are performed on the Wildlife Management Area in its entirety. Sometimes referred to as just "Area."