Hualapai Mexican Vole Conservation Status Review
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August 02, 2015 Hualapai Mexican Vole Conservation Status Review PREPARED BY Amanda Aurora, C.W.B . Eleanor Gladding Regional Scientist / Project Manager Senior Biologist/Project Manager SWCA Environmental Consultants - Austin SWCA Environmental Consultants - Tucson 4407 Monterey Oaks Boulevard, Building 1, Suite 110 343 West Franklin Street Austin, Texas 78749 Tucson, Arizona 85701 [email protected] [email protected] Introduction The Hualapai Mexican vole or Hualapai vole ( Microtus mexicanus hualpaiensis ) is a cinnamon-brown, small mammal in the Cricetidae Family. In January of 1987, the U.S. Fish and Wildlife Service (USFWS) proposed to list the Hualapai Mexican vole as endangered under the Endangered Species Act (ESA) and published the final listing rule in October 1987 (USFWS 1987a; USFWS 1987b). At that time, the species was considered “extremely rare and has among the most restricted habitats of any North American mammal” (USFWS 1987b). The USFWS in the final listing rule identified up to 14 locations in the Hualapai Mountains of west-central Arizona where the Hualapai Mexican vole (or its sign) had been observed (USFWS 1987b) (Figure 1). The USFWS also noted that “from 1923 to the present, only 15 specimens are known to have been captured in the Hualapai Mountains” (USFWS 1987b). This subspecies was differentiated by morphological characteristics from the other subspecies of Microtus mexicanus that occur in Arizona, including M. mexicanus mogollonensis and M. mexicanus navaho . The primary morphological differences differentiating the Hualapai Mexican vole from the other subspecies include: slightly longer body, longer tail, and longer and broader skull (compared to M. mexicanus navaho ) and a longer body, shorter tail, and a longer and narrower skull (compared to M. mexicanus mogollonensis ) (USFWS 2015). In 2004, the Arizona Game and Fish Department (AGFD) submitted a petition to the USFWS requesting that the federal agency delist the Hualapai Mexican vole. In the petition, AGFD presented data to support their assertions that: (1) the subspecies occurs over a much greater area and in higher numbers than previously known; (2) it is likely that all populations referred to as Microtus mexicanus hualpaiensis , along with other populations of the species in Arizona, should be referred to as a single subspecies; and (3) the threats faced by this more widespread taxon do not indicate that listing under the ESA is warranted (AGFD 2004). In 2008, the USFWS published a 90-Day Finding on the AGFD’s 2004 petition to delist the Hualapai Mexican vole. In its finding, the USFWS determined that AGFD presented “reliable and accurate information” in its 2004 petition indicating that the endangered Hualapai Mexican vole, under the 1 August 02, 2015 Known Range at Listing 2 August 02, 2015 scientific name of Microtus mexicanus hualpaiensis , may not be a valid taxon or, if it is valid, then the listed subspecies occurs across a greater range than previously known (USFWS 2008). However, the USFWS was unable at that time to ascertain the correct taxonomic interpretation of the group due to disagreements among peer reviewers on the most recent taxonomic research. Ultimately, the USFWS concluded that “We find that the petition presents substantial information indicating that delisting this mammal may be warranted. We are initiating a status review to determine if delisting this subspecies is warranted” (USFWS 2008). Subsequently on June 4, 2015, the USFWS issued a joint 12-Month Finding on the 2004 delisting petition and a Proposed Rule to delist the Hualapai Mexican vole on the basis that “the currently listed subspecies is not a valid taxonomic entity” (USFWS 2015). In the proposed delisting rule, the USFWS acknowledged that “based on morphological measurements, the Hualapai Mexican vole was previously considered one of three subspecies of Mexican voles ( Microtus mexicanus ) in Arizona,” along with M. mexicanus navaho and M. mexicanus mogollonensis . While USFWS recognized that taxonomic studies completed to date “offer different conclusions about which populations may or may not be Hualapai Mexican voles,” the agency stated that “there is sufficient evidence to indicate that the currently listed entity for the Hualapai Mexican vole [which USFWS notes is limited in distribution to the Hualapai Mountains of west-central Arizona] is no longer a valid taxonomic subspecies” (USFWS 2015). In the proposed delisting rule, the USFWS requested additional information on “the conservation status of Hualapai Mexican voles and Mexican voles in general” and “new information on the historical and current status, range, distribution, and population size of Hualapai Mexican voles, including the locations of any additional populations” (USFWS 2015). In response to their request, this report provides information documenting the current conservation status of the Hualapai Mexican vole and its likely synonymous populations, as well as an evaluation of potential threats to the larger, taxonomically valid species. Taxonomy USFWS (2015) summarized the findings of the various taxonomic studies conducted on Mexican voles in Arizona and the southwestern United States (Table 1). While these various taxonomic studies did not involve specimens from the same locations or distributions, USFWS (2015) recognizes this body of work to be the best scientific information available. The USFWS (2015) notes that five of seven peer reviewers of the most recent taxonomic study by Busch et al. (2001) supported the finding that genetic data do not support the separation of vole populations in Arizona into three subspecies. 3 August 02, 2015 Table 1. Taxonomic studies of Mexican voles in Arizona and the southwest United States. Year and Source Methods and Study Key Findings Distribution of Population Populations Synonymous with Hualapai Mexican Vole* 1987 Morphological variation M. mexicanus hualpaiensis is Hualapai Mountains Final Listing Rule a morphologically distinct (USFWS 1987b) subspecies 1989 Morphological variation Specimens from the Hualapai Mountains; Frey (1989) across the range of M. Bradshaw Mountains, AZ, Bradshaw Mountains mexicanus in the U.S. and should be reassigned from M. Mexico mexicanus mogollonensis to M. mexicanus hualpaiensis 1993 Genetic analysis based on Specimens in Hualapai Hualapai Mountains; Frey and Yates (1993) protein electrophoresis and Mountains, Hualapai Indian Hualapai Indian Reservation; mitochondrial DNA from 13 Reservation, and Music Music Mountains populations across AZ and 1 Mountains are closely related population in Mexico and distinct from other populations in AZ and may be considered to be M. mexicanus hualpaiensis 1995 Genetic analysis based on Specimens from six Hualapai Mountains; Frey and Yates (1995) protein electrophoresis and populations may be M. Hualapai Indian Reservation; mitochondrial DNA from 26 mexicanus hualpaiensis, with Music Mountains; populations across AZ, NM, two other populations Aubrey Cliffs/Chino Wash; UT, and Mexico suspected to be M. Santa Maria Mountains; mexicanus hualpaiensis on Bradshaw Mountains the basis of geographic proximity Possibly also: Round Mountain; Sierra Prieta 2001 Genetic analysis based on Study did not support the Hualapai Mountains; Busch et al. (2001) nuclear markers from 6 separation of Mexican voles Hualapai Indian Reservation; populations in northwest AZ into three distinct Aubrey Cliffs; and mitochondrial DNA from subspecies; specimens Bradshaw Mountains; 13 populations across AZ referred to as M. mexicanus Watson Woods; navaho or M. mexicanus Sierra Prieta; mogollonensis were Navaho Mountain; genetically similar to Minus Mountain; specimens from locations San Francisco Peaks; previously identified as Grand Canyon South Rim containing M. mexicanus Mogollon Rim; hualpaiensis ; only 1 Chuska Mountains; subspecies of Mexican vole White Mountains occurs in AZ *General locations are shown on Figure 1. As presented and discussed in the AGFD’s petition (AGFD 2004) and acknowledged in the USFWS 90-Day and 12-Month Findings (USFWS 2008; USFWS 2015), there is some uncertainty regarding the correct 4 August 02, 2015 taxonomic assignment of Microtus populations in Arizona and elsewhere in the southwest. For context on this issue, the current edition of the Mammals of the World states “Critical overhaul of the mexicanus complex is needed. A phylogeographic approach, integrating morphological and genetic variation across the collective range of these taxa, would offer a firmer basis for delineating species limits and diagnosing them” (Wilson and Reeder 2005). Nonetheless, as summarized by USFWS (2015), the majority of the experts who have reviewed this species complex and the supporting data agree that there is not enough evidence to support the delineation of three subspecies of Microtus mexicanus in Arizona. While most of the research conducted in recent years continues to use the current taxonomic nomenclature of Microtus mexicanus complex of subspecies (including the name M. mexicanus hualpaiensis ), the AGFD and other Microtus researchers believe that the Microtus mexicanus populations in Mexico should retain the name Microtus mexicanus and the populations in the U.S. should be reclassified as Microtus mogollonensis (AGFD 2004). This proposed separation of the two species is already noted on the International Union for Conservation of Nature (IUCN) database (Álvarez- Castañeda and Reid 2008) and the split is also supported by genetic analysis reported by Frey (2009). Further, the AGFD