Mammal Tracks, 2nd ed. and the Elusive House Mouse

North American deermouse. Yosemite National Park, CA. Photograph by Mark Elbroch

Many animal signs have eluded me and caused me concern over the years. House mouse (Mus musculus) footprints were one such sign—I expected I’d seen them, but wasn’t certain. Certainly house mice are supposed to be widespread in some environments, but I’d never actually seen one in the northern woodlands that have for the most part characterized my homes over the last 30+ years.

The answer was to gather footprints from captive mice, and work backwards I figured. With the help of Andy Stratton, we did just that. Their footprints, thank goodness, have some distinctive features and therefore I can be fairly certain that I’ve not often mistaken deermice or harvest mice footprints for those of house mice. With the exception of one important occasion, unfortunately—I misidentified house mouse tracks in the 1st edition of Mammal Tracks and Sign.

It ends up that house mice are well established in reserves and parks bordering San Francisco Bay, where they compete with listed salt water harvest mice. And this is exactly where I’d taken the photograph found on page 593 in the second edition of Mammal Tracks and Sign: A Guide to North American Species, written with Casey McFarland. I’d called them harvest mouse tracks in the first edition, but upon inspection, they clearly aren’t. One quick and easy distinguishing feature useful in their identification is that whereas harvest mice front and hind tracks are of similar dimensions, the hind footprints of house mice are distinctly larger than those of front tracks.

I’m thrilled to finally feel I’ve made some progress with this elusive critter. One box checked, hundreds more to go!


Page 593 in the new edition of Mammal Tracks and Sign where I confess my mistake in the first edition–these are footprints of house mice not harvest mice.

Read Mammal Tracks and Sign, 2nd edition for additional details about house mouse tracks, and countless other tidbits to refine one’s observations in the natural world. The book is slightly taller and wider than the previous edition, but more slender. It feels better in the hand I think. Its just slightly more than 2.8 lbs, or weighs nothing at all as a Kindle file.

It’s dense. The designers really packed it in there, trying to save space everywhere possible to reduce the length of the book. Many images are smaller than I would have liked, but that’s just because I think tracks and sign are beautiful. Educationally, they should suffice.

The contributions of so many other people really elevated this edition to another level. Thank you everyone. Chris Hass shared so much about coatimundis, Preston Taylor and Matt Nelson shared amazing things about wild pigs, and numerous biologists contributed amazing images to expand the chapter on interpreting prey remains. And my CyberTracker evaluator and Specialist colleagues, Jonah Evans, George Leoniak, Dave Moskowitz, Kim Cabrera, Michelle Peziol, and Connor O’Malley contributed so much as well. And that’s just for starters… so many others contributed as well. Thank you all.

Link to the book on Amazon

Link to book on Barnes and Noble

Reflection on Tracker Evaluations in North America

Male mountain lion tracks. Mark Elbroch

Jonah Evans, CyberTracker Evaluator and host of, sent me an audio file of a talk I gave on the CyberTracker Tracker Evaluation system, at the International Society of Professional Trackers in 2005 (I think) in Texas, just before we gave the first tracker evaluation to Texas Parks and Wildlife Department employees responsible for river otter surveys in the eastern portions of the state. It was a historic moment, and tremendous fun to boot. Since then, we’ve evaluated and trained about 90 staff of Texas Parks and Wildlife. They were brave enough to let us assess their staff, and it was the perfect launch to North American tracker evaluations–working with people who utilize tracking skills in their everyday work and lives. I wouldn’t have had it any other way.

Moose trail, Grand Teton NP, Wyoming. Mark Elbroch

Its a long talk (link below), just to warn you, but mostly anecdotal and hopefully entertaining. Its fun to look back and consider how far the system has grown in this country over the last 14ish years. If we include those in training, we’ve about a dozen evaluators working across North America now, spreading the system created by Louis Liebenberg so many years ago in South Africa. Numerous countries have hosted evaluations around the globe, ranging from Spain to Denmark to Vietnam to Botswana to Canada. The system continues to grow.

Thank you everyone who has contributed to its success.

Link to the talk.

Eastern Cougar “Extinction” — Some Key Points


The eastern cougar is not extinct, it never existed–here is a mountain lion from the west, which genetics confirm is as much an eastern cougar as those cats that historically roamed New England.

I’ve received a lot of worried messages and comments on social media about the recent U.S. Fish and Wildlife declaration that the “eastern cougar” (or mountain lion, Puma concolor couguar) is extinct, and was therefore being removed from federal endangered species protections. I think the wording of the federal ruling unintentionally—but unfortunately—influenced how the media covered the change in conservation status.

Here is the complete federal ruling, but here I provide what I believe are the five key take-home messages for those of us invested in mountain lion conservation. This is just one man’s opinion, of course.

  1. There never was an “eastern puma/cougar.”

This is one point I believe should have been included in the summary at the start of the federal ruling. Yes, the fact that there is not a breeding population of “eastern cougars” in the northeast of the United States or eastern-most Canada is reason for the declaration. But, much more importantly, the newest science has revealed that there never was an “eastern cougar” subspecies to begin with.

Phylogeny is the science that proposes how animals are related by their evolutionary history. Think of phylogentic trees, something most people can remember from school, and the “tree of life” showing how animals evolved and are related to each other. Today, phylogenetics is the more appropriate term, because our study of phylogeny is almost entirely dependent upon genetic tools.

In the old days, phylogeny was proposed based upon morphology (the shape, color, and external characteristics of an animal and its skeleton). Based upon subtle differences in coat color and skeletal measurements, historic scientists believed there were many subspecies of mountain lions in North America, including the eastern cougar. Genetic tools, however, have provided a very different picture.

The International Union for Conservation of Nature (IUCN) currently recognizes six subspecies of mountain lions, of which only one—Puma concolor cougar—inhabits North America. This means that current genetic research supports the belief that all the mountain lions in North America are of a single subspecies. In other words, the eastern cougar was never a separate subspecies, and mountain lions that historically inhabited the northeast of North America were the same subspecies as the mountain lions in Idaho—which are still very much alive. Thus, the eastern cougar is not extinct—it never existed.

It is more correct to say that the North American subspecies of mountain lions is locally extinct in the northeast, because there is not a breeding population in this region.

  1. Recent and future mountain lions in the northeast are not eastern mountain lions.

Any recent news of mountain lion sightings in the northeast, and any future confirmations of mountain lions in the northeast, do not justify the existence of the “eastern cougar” as a separate subspecies. These are migrants from the west, not local mountain lions that survived undetected for the last 70 years. Even if there was evidence that some of these new migrants were breeding, that is still not evidence of eastern mountain lions. These are the North American subspecies of mountain lions returning to where they were extirpated some 70 years ago when wide-scale predator control was commonplace.

Tracks of an adult female mountain lion from northwest Wyoming (F72). Photograph by Mark Elbroch

Some people still argue that mountain lions have existed in hidden pockets in New England for all of these years. Importantly, this does not matter because the subspecies distinction of “eastern cougar” was incorrect. But, further, most people agree this is unlikely. New England has numerous people skilled in interpreting animal tracks and sign, and mountain lions leave considerable sign where they move and kill prey.

Consider the amazing adventure of the dispersing male mountain lion that was killed on a Connecticut highway in 2011—and subsequently became national news and was written up in the book Heart of a Lion. Documenting this lone male was akin to looking for a needle in a haystack when you consider the massive geographic range he traversed, in which he unlikely ever encountered another mountain lion east of the Mississippi (if not east of Kansas). Yet, even he was documented numerous times on motion-triggered cameras and by experienced woodsmen and women while he traveled. Paul Rezendes and I were two of the many that confirmed photos of footprints he left in the Quabbin Resevoir in central Massachusetts before he was killed. My point is that even a single cat without a territory leaves sign, and a resident breeding population leaves much more.

  1. Eastern migrants are unaffected.

Mountain lions that disperse eastward from the west were never protected under the Endangered Species Act. Thus, current and future eastern migrants are unaffected by the new federal ruling—and still protected following the laws of the states in which they move while they are dispersing to seek new territories to call their own.

This map was made by Brad Herried for the Cougar Network, an organization leading the documenting and analyzing the eastward expansion of western mountain lions.

  1. Introducing mountain lions in the east just got easier (probably).

Re-introducing animals into previous range (as was done with wolves into Yellowstone National Park and central Idaho in 1995 and 1996) is an arduous process. Re-introducing federally protected animals, which are monitored closely and have stringent rules about how they are handled and moved, is even more difficult.

The U.S. Fish and Wildlife Service and numerous conservation scientists agree that delisting the eastern cougar actually makes it easier to reintroduce this top predator in the northeast. For one reason, now that all mountain lions in North America are considered the same species, we can reintroduce the native subspecies to New England rather than replace it with a different subspecies. It will now be up to each state to decide whether that is a course they would like to pursue, however, the debates between pro-predator and anti-predator constituents are unlikely to be any easier

If you live in an eastern state that is deliberating reintroduction, or if you would like then to consider it as an option, get involved, reach out and contribute your thoughts. State Wildlife Agencies act on behalf of their public—so let them know how you feel. Certainly, there are numerous areas that could sustain mountain lions in the northeast.

  1. The Florida panther is unaffected (at least for now).

The Florida panther, Puma concolor coryi, is listed separately from the eastern mountain lion, and its status under the Endangered Species Act is unaffected by the recent federal ruling. The 80-100 wild Florida panthers remain protected wherever they are found, even if they disperse out of Florida into neighboring states.

The caveat, however, is that current phylogentics could be used to argue that the Florida panther subspecies, just like the eastern cougar, is not justified either, and that their protective status should be ended as well. This would be devastating for Florida panther conservation, which is currently led by the U.S. Fish and Wildlife Service. This is something conservation scientists, advocates, and managers need to monitor closely as the status of Florida panther is reviewed by the U.S. Fish and Wildlife Service.

The Importance of Fieldwork and Field Skills

Young male mountain lion with a mule deer fawn killed by his mother.

Among my favorite activities is investigating mountain lion kill sites—meaning the work of actually going into the field and finding the remains of prey killed by mountain lions. We just published new research in the Journal of Mammalogy that shows that these expeditions in search of prey remains are not just enjoyable, they are also the best way to study carnivore foraging behaviors.

Every kill site is different, and some are tough to find. But over the years, I’ve begun to better predict where a cat might feel secure enough to feed and hide the remains of their prey. Flies are a great clue too—the sound and sight of them have often drawn me to a hidden carcass or a subtle area blood-flecked and sprinkled with tiny bits of tissue and bone easily overlooked. Magpies and eagles are even better, their vocalizations provide guidance from afar and if you can spot them on the ground, then you’ve found your kill.

Modern research on mountain lions relies heavily upon GPS technology built into collars. Location data are transferred via satellites to our computers while the collar is still on the cat, thus we can follow them in near real time. It’s absolutely amazing. When we see a group of location points on a map, we know a mountain lion has remained in place for some duration—what that animal was doing can only be determined with certainty by visiting the site to see what happened (and even then its not certain because we rely upon tracking skills to interpret signs; tracking will always be an imperfect art and science).

An elk killed and cached by a female mountain lion in northwest Wyoming.

Now it might be apparent to those who know me—that studying mountain lion kill sites brings together my dual interests in wildlife tracking and mountain lions. Its as if this work were created with me in mind. For the most part, our research teams (including those with professional tracking skills: Casey McFarland, Neal Wight, Matt Nelson, Max Allen, Michelle Peziol, Connor O’Malley, Anna Kusler, Blake Lowrey, and myself) spend almost all of our time visiting these sites in the field—its time consuming work, but I believe, well worth the effort.

Other researchers, however, invest elsewhere, and rely upon statistics and mathematics to measure kill rates (how often a carnivore kills prey) and even prey selection (what carnivores eat). They do this by visiting just a sample of locations in the field and then extrapolating what they observed to every area a mountain lion or other carnivore stopped and spent time, with the help of complex mathematical models. This approach is appealing because it saves lots of time in the field, and therefore money. Thus, the mathematical method has spread rapidly across the globe where it is being applied to more and more carnivore species.

My coauthors, Blake Lowrey and Heiko Wittmer, and I tested this mathematical approach to estimating kill rates against our own heavy-fieldwork approach, in which we try to visit every location a mountain lion stops for 4 or more hours on the landscape (we used to do 2 or more hours but 2-hr sites yielded very little prey data). We did this for 3 different study systems in which we’ve worked (Chilean Patagonia, Northern California, western Colorado), and found that the mathematical approach yielded unpredictably, inaccurate and imprecise estimates of kill rates. This was mostly due to the fact that carnivores are inconsistent in how they feed. They eat prey of different sizes, so the associated time it takes to consume their kills is highly variable. Mountain lions and other carnivores also have their kills stolen by bears and condors, and thus they sometimes feed for very short time periods from a large animal they killed. This confuses computer models, which tend to predict that places where a mountain lion spent little time must have been a place where it rested rather than killed prey.

An adult female mountain lion stands over an 11-month old elk calf she killed and cached.

Fieldwork is not just enjoyable, its justifiable. Spending time in the field remains our best approach to studying carnivore diets and kill rates. This is excellent news for those of us that have invested so much time in learning tracking skills, and so delight in forays afield where we apply our trade.