Wolf populations are expanding in the western states. It started with the introduction of wolves into Yellowstone National Park and central Idaho in the 1990s, which was followed by wolves spreading across Montana, Wyoming, Idaho, Washington, Oregon and northern California. Wolves were transplanted into Colorado in 2023 and 2025. Mexican wolves were maintained in captivity, followed by releases into the wild in Arizona and New Mexico.
Wolves kill livestock and negatively affect ranchers. Recent issues of the WLJ have several Story Shorts articles on wolves in the western states. The July 28 and Aug. 4 issues of WLJ report that Colorado has three new wolf packs, and plans to release more wolves next winter in southwestern Colorado, including Gunnison County. The Aug. 4 WLJ reports that a Mexican wolf moved north of Interstate 40 in New Mexico, which is the northern boundary of the Mexican wolf range. I will explain why this is an important science issue.
The wolves in all of the western states except New Mexico and Arizona are the northern wolf subspecies, originally imported from Canada for the 1990s transplants to Montana, Idaho, and recently, to Colorado. The wolves in New Mexico and Arizona are the Mexican wolf subspecies. I’ve written in the WLJ and science journals about the indefinite nature of subspecies, including wolf subspecies (see the References below). Subspecies are populations in different geographic areas with different characteristics like coat color, size and genetics. Subspecies belong to the same species and can interbreed. Subspecies are like livestock breeds, but without the controlled mating that maintains livestock breeds as genetically different.
Wildlife, including wolves, disperse and interbreed among areas. This makes the subspecies category indefinite because of genetic mixing over space and time. But the Endangered Species Act (ESA) allows the listing of subspecies, not only an entire species, as endangered. The Mexican wolf is listed as an endangered subspecies in Arizona and New Mexico, separate from wolves in the other 48 contiguous states. Wolves are not listed as endangered in Alaska, Montana, Wyoming, Idaho and eastern Washington and Oregon. Wolves are listed as an endangered species, called a distinct population segment (DPS), in the rest of the 48 contiguous states. This is confusing because the ESA can consider species, subspecies and DPSs as endangered. The federal government is managing subspecies and DPSs, which are populations, with the ESA, but managing wildlife populations is a state function. Because science shows that subspecies and DPSs are not definite groups, the government has been using the ESA with indefinite science without fully acknowledging it.
The Mexican wolf and northern wolf subspecies are likely to mix as their ranges expand (see the References). Northern wolves have moved into Arizona and New Mexico in the past, and the recent movement of a Mexican wolf north of I-40 near Mount Taylor and the plan to bring wolves to southwest Colorado indicate the subspecies’ ranges will likely overlap at some time. Gunnison, CO, to Grants, NM, near Mount Taylor is about 400 miles, which is within the travel distances recorded for wolves.
Does it matter if northern wolves and Mexican wolves interbreed? Wolf populations have always increased, decreased and interbred over their ranges. Some biologists consider mixing the wolf subspecies as good because it will increase genetic variation, like crossbreeding livestock. Other biologists consider mixing the wolf subspecies as not good because it will change the genetics of the Mexican wolf. It’s not clear if or how the northern and Mexican wolves will be prevented from mixing, or if it’s scientifically good or bad.
Biologists and environmental groups insisted that the Mexican wolf be designated a subspecies which led to their listing as an endangered species under the ESA. The government decided the Mexican wolf was a legitimate subspecies, even though the scientific literature shows that subspecies are not definite. Whether this is biased science or simply opinion, it’s not definite science.
The problem is that the ESA includes subspecies and DPSs as “species.” Good wildlife management is focused on populations in geographic areas, like your state’s game management units. But is the ESA meant to manage populations or entire species? Congress needs to address this question. ESA listings result in the federal government seizing wildlife jurisdiction from states using the indefinite science of subspecies and DPSs. It’s a science issue, and the ESA is not using rigorous science.
Some biologists think subspecies are legitimate and disagree with descriptions of the indefinite nature of subspecies. But many scientists have written about the indefinite nature of subspecies and populations (DPSs) in the scientific literature (see the References). This must be acknowledged for the ESA to use the best science. This is important because wolves protected by the ESA are killing livestock and hurting American ranchers and agriculture. — Dr. Matt Cronin, WLJ columnist
(Matt Cronin is a biologist with Northwest Biology and Forestry Company LLC in Bozeman, MT, and a teaching professor at Montana State University. He may be contacted at croninm@aol.com.)
References
Western Livestock Journal Articles Available from M. Cronin (croninm@aol.com)
April 2024. Black and gray wolves. Western Livestock Journal.
November 2023. Wolves in Colorado and Mexican wolves. Western Livestock Journal.
August 2023. Possible black wolf sighting in Arizona. Western Livestock Journal.
June 2023. Wolf ESA populations are too complicated. Western Livestock Journal.
May 2023. Draft EIS for introducing wolves to Colorado. Western Livestock Journal.
March 2023. Predicting the numbers of wolves in Colorado. Western Livestock Journal.
March 2022. Wolves-When north meets south. Western Livestock Journal.
April 2021. An assessment of wolf numbers and predation in Colorado. Western Livestock Journal.
July 2020. Wolves in Colorado. Western Livestock Journal.
April 2020. Livestock losses to wolves: Insights for Colorado. Western Livestock Journal.
February 2019. Wolf species, subspecies, populations and the ESA. Western Livestock Journal.
Subspecies references (see the references in these papers for a complete understanding of subspecies)
Avise, J.C. 2000. Phylogeography, the History and Formation of Species. Harvard University Press, Cambridge, Massachusetts.
Bergstrom, C.T. and L.A. Dugatkin. 2023. Evolution 3nd edition. W.W. Norton & Company, New York.
Carey, J. 2023. Wolf observation report by Catron County Wildlife Investigator. Catron County, New Mexico Information Investigation Report, Case Number IR-052.
Cavalli-Sforza, L.L., P. Menozzi, and A. Piazza. 1994. The History and Geography of Human Genes. Princeton University Press, Princeton, New Jersey.
Darwin, C. 1871. The Descent of Man and Selection in Relation to Sex. Murray, London. Republished in 1981, Princeton University Press, Princeton, New Jersey.
Dawkins, R. 2004. The Ancestor’s Tale. Houghton Mifflin Company, New York.
Ehrlich, P.R. 2000. Human Natures. Island Press, Shearwater Books, Washington, D.C.
Fredrickson R, Hedrick PW, Wayne RK, vonHoldt BM, Phillips M. 2015. Mexican wolves are a valid subspecies and an appropriate conservation target. Journal of Heredity 106:415-416.
Futuyma, D. J. and M. Kirkpatrick. 2017. Evolution 4th edition. Sinauer Associates, Sunderland, Massachusetts.
Haig, S.M., E.A. Beever, S.M. Chambers, H.M. Draheim, B.D. Dugger, S. Dunham, and E. Elliott-Smith. 2006. Taxonomic considerations in listing subspecies under the US Endangered Species Act. Conservation Biology 20:1584–1594.
Jimenez, M.D., E.E. Bangs, D.K. Boyd, D.S. Smith, S.A. Becker, D.E. Ausband, S.P. Woodruff, E.H. Bradley, J. Holyan, and K. Laudon. 2017. Wolf dispersal in the Rocky Mountains, western United States: 1993-2008. Journal of Wildlife Management 81:581-592.
Mayr, E. 1954. Change of genetic environment and evolution. Pages 157-180 In: Evolution as a Process. J. Huxley, A. C. Hardy, and E. B. Ford Editors. Allen and Unwin, London.
Mayr, E. 1970. Populations, species, and evolution. Belknap Press, Harvard University Press, Cambridge, Massachusetts.
Mayr, E. 1982. The Growth of Biological Thought. Belknap Press, Harvard University Press, Cambridge, Massachusetts.
National Academies of Sciences, Engineering, and Medicine. 2019. Evaluating the Taxonomic Status of the Mexican Gray Wolf and the Red Wolf. Washington, DC: The National Academies Press. https://doi.org/10.17226/25351.
O’Gara, B.W. 2002. Taxonomy. Pages 3-65 In: North American Elk: Ecology and Management. D. E. Toweill and J. W. Thomas Editors. Smithsonian Institution Press, Washington D.C. and London.
Patten, M.A. Remsen Jr JV. 2017. Complementary roles of phenotype and genotype in subspecies delimitation. Journal of Heredity 108:462-464. doi:10.1093/jhered/esx013.
Vanzolini, P.E. 1992. Third world museums and biodiversity. Pages 185–198 In: Systematics, Ecology, and the Biodiversity Crisis. N. Eldredge Editor. Columbia University Press, New York.
Weckworth B, Dawson N, Talbot S, Cook J. 2015. Genetic distinctiveness of Alexander Archipelago wolves (Canis lupus ligoni): reply to Cronin et al. (2015). Journal of Heredity 106:412-414. doi: 10.1093/jhered/esv02
Wilson, E.O. and W.L. Brown. 1953. The subspecies concept and its taxonomic applications. Systematic Zoology 2:97–122.
Zink, R.M. 2004. The role of subspecies in obscuring avian biological diversity and misleading conservation policy. Proceeding of the Royal Society of LondonB 271:561-564.
Zink, R.M., G.F. Barrowclough, J.L. Atwood, and R.C. Blackwell. 2000. Genetics, taxonomy and conservation of the threatened California Gnatcatcher. Conservation Biology14:1394-1405.
Zink, R.M., J.G. Groth, H. Vaquez-Miranda, and G.F. Barrowclough. 2014. Phylogeography of the California gnatcatcher (Polioptila californica) using multilocus DNA sequences and ecological niche modeling: implications for conservation. Auk 130:449-458.
Cronin, M.A., A. Cánovas, A. Islas-Trejo, D.L. Bannasch, A.M. Oberbauer, and J.F. Medrano. 2015. Single nucleotide polymorphism (SNP) variation of wolves (Canis lupus) in Southeast Alaska and comparison with wolves, dogs, and coyotes in North America. The Journal of Heredity 106:26-36.
Cronin, M.A., A. Cánovas, A. Islas-Trejo, D.L. Bannasch, A.M. Oberbauer, and J.F. Medrano. 2015. Wolf Subspecies: Reply to Weckworth et al. and Fredrickson et al. J. Hered. 106:417-419.
Cronin, M.A., M.D. MacNeil, N. Vu, V. L. R. Leesburg, H. Blackburn, and J. Derr. 2013. Genetic variation and differentiation of extant bison subspecies and comparison with cattle breeds and subspecies. Journal of Heredity. 104:500-509.
Cronin, M.A. 2019. Resource Science: Spotted Owls and the Timber Wars. Western Livestock Journal, 10 June 2019.
Cronin, M.A. 2021. Wildlife, War, and God: Insights on science and government. Second Edition. Matthew A. Cronin, Produced and distributed by Liberty Hill Publishing, Maitland, Florida. First edition published in 2019.
Cronin, M.A. and L.D. Mech. 2009. Problems with the claim of ecotype and taxon status of the wolf in the Great Lakes region. Molecular Ecology 18:4991-4993.
Cronin, M.A. 2007. The Preble’s meadow jumping mouse: subjective subspecies, advocacy and management. Animal Conservation 10:159-161.
Cronin, M.A. 2006. A Proposal to eliminate redundant terminology for intra-species groups. Wildlife Society Bulletin 34:237-241.
Cronin, M.A., M.D. MacNeil, and J.C. Patton. 2006. Mitochondrial DNA and microsatellite DNA variation in domestic reindeer (Rangifer tarandus tarandus) and relationships with wild caribou (Rangifer tarandus granti, Rangifer tarandus groenlandicus, and Rangifer tarandus caribou). Journal of Heredity 97:525-530.
Cronin, M.A. 2003. Research on deer taxonomy and its relevance to management. Ecoscience 10:333-343.
Cronin, M.A. 1997. Systematics, Taxonomy, and the Endangered Species Act: The Example of the California Gnatcatcher (Polioptila californica). Wildlife Society Bulletin 25:661-666.
Cronin, M.A. and V.C. Bleich. 1995. Genetic (mitochondrial DNA) variation among populations and subspecies of mule deer in southern California. California Fish and Game 81:45-54.
Cronin, M.A. 1993. Mitochondrial DNA in wildlife taxonomy and conservation biology: cautionary notes. Wildlife Society Bulletin 21(3):339-348.
Cronin, M.A. 1991. Mitochondrial and nuclear genetic relationships of deer (Odocoileus spp.) in western North America. Canadian Journal of Zoology 69:1270-1279.
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