12-MONTH ADMINISTRATIVE FINDING, BLACK-TAILED PRAIRIE DOG
Chapter 4 Table of Contents
4.2 Listing Priority Number for the Species
The Act requires the Service to make a finding regarding the potential listing of any species based solely on the best scientific and commercial information available. After a review of the petition and supplemental information, the pertinent literature and other scientific data, and statements submitted by States, Tribes, Federal Agencies and other entities, the Service believes that sufficient information is currently available to support a determination that listing the black-tailed prairie dog as threatened is warranted.
A listing of the black-tailed prairie dog as threatened is warranted because of the number and variety of threats adversely affecting the status of the species, both alone and in concert. A significant recent decline in black-tailed prairie dog occupied habitat has been due to several factors, the most influential of which is the widespread occurrence of plague, an exotic and completely lethal disease to the species. In concert with plague, the loss of suitable habitat and inadequate regulatory mechanisms have adversely affected remnant fragmented populations. The available information indicates that the species is likely to become endangered throughout all or a significant portion of its range in the foreseeable future, i.e., meets the definition of a threatened species.
A major decline in historic black-tailed prairie dog occupied habitat has occurred (perhaps as much as 99 percent at present). Sixty percent of the species remnant occupied habitat is vulnerable or very vulnerable to the effects of habitat loss or modification, disease, inadequate regulatory mechanisms, and other factors in an area covering 84 percent of the historic range (Areas 1-6, Figure 3).
Approximately 30 percent of areas along the periphery of the historic range no longer supports any appreciable number of black-tailed prairie dogs (Areas 1, 2, 3, and 6; Figure 3). Approximately 37 percent of the suitable habitat within the species historic range in the United States has been fundamentally modified via conversion to cropland and is not available for use by the species (Table 2). Additionally, habitat in approximately 66 percent of the historic range of the species has been degraded by the occurrence of plague. These estimates are not additive inasmuch as several factors can affect any given portion of the range.
Notably, while black-tailed prairie dog population levels have remained relatively stable in parts of the eastern portion of the species range over the last 10-15 years, the best available information indicates they have declined in the western portion where plague occurs (Figure 4). Trends may be more indicative of population impacts than the absolute magnitude of declines, if rates of increase in some areas after the 1972 toxicant ban are contrasted with rates of decline after plague reports increased in the 1980s and 1990s. The shifting trends in extant black-tailed prairie dog occupied habitat from one of remarkable increases from approximately 1972 to 1980 (although not approaching historic levels) to marked declines from approximately 1980 to 1999 suggests the presence of a significant widespread depressant influence such as disease in many areas. Other factors also have limited population growth across the range as well, particularly in South Dakota where control efforts at Pine Ridge in the early 1980s resulted in a significant decrease in occupied habitat (Figure 5).
Recent, widely-separated, site-specific declines in 50 percent of the black-tailed prairie dog historic range where 60 percent of current rangewide populations occur (Area 4) appear to be indicative of a general population decline similar to that observed across the State of Montana from 1986 to 1998 (Montana Department of Fish, Wildlife and Parks 1998). In Montana, approximately 50 percent of all black-tailed prairie dog occupied habitat was lost, largely due to plague, from 1986 to 1998. Plague has incrementally extended its range and impacts on black-tailed prairie dogs since it was first reported in the literature in 1946. It may continue to expand into the eastern portions of the species range (Areas 7 and 8) in the immediate future. This likelihood is evidenced by recent reports of plague exposure to predator species in previously unaffected portions of the range. A similar decline can be expected for populations in Mexico (Area 5), 12 percent of current rangewide populations, where habitat loss due to cropland conversion is occurring. Assuming this pattern of decline persists across Areas 4 and 5, and plague manifests itself in Areas 7 and 8 (Figure 3) over the next 30 years, then existing black-tailed prairie dog occupied habitat could decline to as low as approximately 10 percent of current estimates for remnant populations. At present, occupied habitat has decreased over the past century by two orders of magnitude (from approximately 100 million acres to less than 1 million acres). In 30 years, occupied habitat could decrease by another order of magnitude to approximately 0.1 percent of historic estimates.
4.2 LISTING PRIORITY NUMBER FOR THE SPECIES
At present Region 6 has 26 proposed and candidate species and/or subspecies to address in addition to consideration of the required listing action pursuant to this 12-month finding. Service policy (48 FR 43098) requires the assignment of a listing priority number (LPN) to all candidate species that are warranted for listing. This listing priority system was developed to ensure that the Service has a rational system for allocating limited resources in a way that ensures that the species in greatest need of protection are the first to receive such protection. A smaller LPN reflects a need for greater protection than a larger LPN. The LPN is based on the magnitude and immediacy of threats and the species taxonomic uniqueness with a value range from 1 to 12 (Table 3).
The Service has provided guidance on evaluating the magnitude and immediacy of threats (48 FR 43104). The first criterion to consider is the magnitude of threats. Species facing the greatest threats to their continued existence should receive the highest consideration for listing based on the highest magnitude of threat. The second criterion to consider is the immediacy of threats. Species facing actual, identifiable threats should be given priority over potential threats. In assigning a species to a priority category regarding immediacy, the Service should consider the known occurrence or lack of documented detrimental trade or harvest, habitat modification, significantly detrimental disease or predation, and other present or potential threats. The third criterion to consider assigns priority to species that represent highly distinctive or isolated gene pools.
The Service has evaluated the magnitude and immediacy of threats to the black-tailed prairie dog as discussed in this finding. The following is a summary of these evaluations. The black-tailed prairie dog is considered a species under the third criterion mentioned above (Table 3).
!The Present or Threatened Destruction, Modification, or Curtailment of the Species Habitat or Range.
Habitat loss and fragmentation are considered a threat of moderate magnitude. The species has lost 99 percent of its historic occupied habitat, much of it through cropland conversion, largely in the eastern portion of the species range. However a considerable amount of potential unoccupied habitat remains, especially in the western portion of the species range. This unoccupied habitat could be utilized if other factors such as control efforts and disease were not present or carefully managed via adequate regulatory mechanisms.
This threat is considered imminent because habitat loss continues at present through cropland conversion, urbanization, change in vegetative communities, etc. Suitable habitat can be unavailable or degraded due to fragmentation, isolation, and/or the presence of disease in reservoir species.
!Overutilization for Commercial, Recreational, Scientific, or Educational Purposes.
Overutilization via commercial use of the species as a pet is not considered a threat, given the apparent low number of individuals utilized.
Overutilization via recreational shooting is considered a threat of low magnitude. Local populations may be impacted by shooting; however, significant rangewide population declines due to this factor are not likely.
This threat is considered imminent because it is ongoing.
!Disease or Predation.
Disease is considered a threat of moderate magnitude because it is not affecting all populations at once and since some recovery may occur, largely via unaffected adjacent populations, before its reoccurrence. Plague has impacted the species and its conspecifics throughout a significant portion of their ranges. Plague first occurred in Gunnisons prairie dogs in Arizona in the 1930s and in Colorado in the 1940s. Plague first occurred in black-tailed prairie dogs in Texas and Montana in the 1940s, and could spread eastward to the remainder of the black-tailed prairie dog range. Black-tailed prairie dogs suffer nearly 100 percent mortality when exposed to plague. An epizootic may affect an entire complex as if it were an individual animal affected by a pathogen. The spread of plague eastward in black-tailed prairie dog populations underscores the likelihood that unaffected areas may experience outbreaks. Plague is a new phenomenon in North American ecosystems. Its impacts may be as dramatic as those caused by other non-native invasive species.
This threat is considered imminent because it is ongoing.
Predation is not considered a threat.
!Inadequacy of Existing Regulatory Mechanisms.
Existing regulatory mechanisms are inadequate and considered a threat of moderate magnitude. All States within the current range of the black-tailed prairie dog classify the species as a pest for agricultural purposes and either allow or require its eradication. Few regulatory mechanisms exist to aid in conserving the species.
This threat is considered imminent because it is ongoing. State wildlife agencies and other interested parties are developing a draft conservation plan for the species. While we believe that this is a good beginning in addressing the conservation needs of the black-tailed prairie dog, this document lacks commitments to specific immediate actions that would affect the status of the species. However, implementation of specific actions developed under this Strategy could have a positive impact on the species status in the future.
!Other Natural or Manmade Factors Affecting its Continued Existence.
Control programs conducted largely in response to concerns related to potential forage competition with domestic livestock are considered a threat of moderate magnitude. Control programs have had significant impacts on population levels in the past. Control efforts resulted in extirpation of the black-tailed prairie dog from Arizona and significant reductions in populations in other States. Current control efforts may impact 10-20 percent of the species overall population annually.
This threat is considered imminent because it is ongoing. Control efforts in some areas could likely be accommodated if adequate regulatory mechanisms were in place which balanced agricultural and wildlife conservation interests.
The synergistic effects of various factors adversely influencing black-tailed prairie dog populations are largely unknown. Nevertheless, these influences are considered a moderate threat because of known exacerbating influences such as isolation of scattered populations.
This threat is considered imminent because it is ongoing.
The Service has concluded that the overall magnitude of threats to the black-tailed prairie dog throughout its range is moderate and the overall immediacy of these threats is imminent. The black-tailed prairie dog is considered a species pursuant to its genetic status. Pursuant to the Services Listing Priority Policy, a species for which threats are determined to be moderate and imminent is assigned a LPN of 8 (Table 3).
Under the Services Listing Priority Guidance for Fiscal Year 2000 (99 FR 57114) the Service prioritizes among the various listing activities. Highest priority is given to emergency listings, next priority to processing final decisions on already proposed listings, next priority is given to candidate species, and the lowest priority to responding to petitions. Region 6 currently has four species proposed as endangered or threatened including lynx (Lynx canadensis), Yermo xanthocephalus (desert yellowhead), mountain plover (Charadrius montanus), and Gaura neomexicana ssp. coloradensis (Colorado butterfly plant). Proposed rules for two other plant species, which were previously candidate species, have been developed and submitted for review. Critical habitat designation for species already listed also may become a higher priority if court action requires us to develop designations. Region 6 is currently under a court order to designate critical habitat for the Virgin River chub (Gila robusta seminuda), and is involved in settlement of a court case which will result in designation of critical habitat for the piping plover (Charadrius melodus).
Region 6 currently has 9 candidate species or subspecies that have lower LPNs, and, therefore, are in more immediate need of protection (Table 4). There are currently three species or subspecies with a LPN of 8. Those species or subspecies with lower LPNs include the sicklefin chub (Macrhybopsis meeki), sturgeon chub (Macrhybopsis gelida), fat-whorled pond snail (Stagnicola bonnevillensis), Astragalus tortipes (Sleeping-Ute milk-vetch), boreal toad (Bufo boreas boreas), Arkansas darter (Etheostoma cragini), Penstemon grahamii (Graham beardtongue), Penstemon debilis (parachute beardtongue), and Penstemon scariosus var. albifluvis (White River beardtongue). Other species or subspecies with the same LPN are swift fox (Vulpes velox), Castilleja aquariensis (Aquarius Indian paintbrush), and Astragalus equisolensis (Horseshoe milk-vetch).
The Service believes that sufficient information is currently available to support a decision that listing the black-tailed prairie dog as threatened is warranted, but that a proposed rule at this time is precluded by work on other higher priority species. The Service will re-evaluate the status of the species 1 year after publication of this finding in the Federal Register.