Mammalian species prioritization scale

Hello all,

The write-up took much longer than I had anticipated – came out to 10 pages – for which I apologize sincerely. But finally, here is the scale for ranking mammals’ `desirability’, or prioritizing mammal-watching efforts by species. Attached herein as a PDF.

Hopefully it will be of value to all. Please do provide feedback, as this is the first time I am sharing this scheme with others.



Best regards,

-Eran Tomer

Atlanta, Georgia, USA


  • Leslie Sokolow

    I enjoyed this a lot. I still remember the thrill of seeing my first short-tailed shrew as s college student , so I wouldn’t rank it so low. Also give the difficulty of seeing polar bears in the wild, it requiring its own expedition, I’d say it’s on par with African big game animals.

    • Eran Tomer

      Thank you, Leslie. Personally I wouldn’t rate Short-tailed Shrews this low either (nor House Mouse, a lovable little beastie). These ratings were suggested only by virtue of comparison to other species. I too get thrills from observing these shrews, which I see infrequently here in Georgia. In fact, I should post about a very interesting encounter I had with one. Just made a note of it.

      Relatedly: I absolutely cannot read “Blarina” without thinking, “Ballerina”. I have visions of this small, chubby, mole-like creature performing elegant pirouettes in a tutu and ballet shoes… If only I could draw it. I’m no good at drawing.

      Best wishes,

      – Eran

      • Leslie

        Eran, I too live in Atlanta. I’m surprised we have t run into each other yet.

        • Eran Tomer

          Hi again,

          Goodness, small world. The Atlanta metro area is the nation’s 9th largest, vast enough for people to live here for years and never cross paths.

          If you are interested, I invite you to join the Georgia wildlife discussion list, GOWFOR-L, which I launched back in 2003. Not strictly mammal-focused but the only mailing list where observations of GA mammals can be posted and discussed. You can read more about it at:

          And look at the archives at:

          In fact, I posted about a Coyote just yesterday. And if you are interested in birds, there is also the Georgia birding list GABO-L at:

          If I can be of any assistance to you, pleast e-mail me directly: erantomer (AT)

          Best wishes,

          – Eran

  • John Fox

    I also enjoyed this post, Eran.

    I rate monotypic taxa highest because they are at the end of a very long evolutionary line. Mountain Beaver (Aplodontia rufa) and Round-tailed Muskrat (Neofiber alleni) in North America, for example. A. rufa is not that hard to find, N. alleni is very hard. That’s what makes it all fun, eh?

    My favorite by far is Monito del Monte. From Wiki:

    “It is the only extant species in the ancient order Microbiotheria, and the sole New World representative of the superorder Australidelphia (all other New World marsupials are members of Ameridelphia).”

    That this mammal’s lineage may go back 55 million years and it is the last one stirs my imagination like nothing else.


  • Vladimir Dinets

    Finding a non-feral, non-introduced house mouse is not a trivial task. It’s original range is still uncertain, so to be 100% sure you have to find it in remote areas of Afghanistan or eastern Iran with no human settlements within at least 25 km. And there are a few well-defined subspecies, at least two of which might eventually be split, so to be certain you have to find it on both sides of the Hindu Kush and also in the Iranian part. Just imagine yourself explaining all this to a local Taliban leader during a highway hold-up, while his subordinates rummage through your stash of Sherman traps 🙂

  • Vladimir Dinets

    As for black and Norway rats, it’s also anything but boring. Black rat belongs to a clade with mostly SE Asian distribution, but introduced populations in Europe and elsewhere appear to originate in SW India. It is unclear what the original range was, but I suspect that black rats in Western Ghats are 100% native. They are not easy to see there. Here is an interesting paper on the history of black rats in Europe.

    Norway rat apparently originates from steppe wetlands of N China, E Mongolia and adjacent parts of Russia; it is a shy rodent that lives in well-hidden burrows and is no easier to see than round-tailed muskrat. Zhalong Nature Reserve in Heilongjiang Province is a good place to try, but you have to get well away from the headquarters area where feral rats are present.

  • Steve Morgan

    Interesting attempt to introduce logic into something that is basically entirely subjective. But have you forgotten behaviour? I’d love to see, for example, an Australian Pebble Mouse. It’s a petty unremarkable creature visually but just look at the pebble mounds it spends its entire life building! Having seen the huge mounds, now I’d like very much to see the builder. Also, consider Striped Dolphin. I’ve seen them lots of times and they’re a fairly common species. But I never tire of watching their exuberant antics, leaping miles of the water and doing all sorts of acrobatics. They seem to have such fun! What the animal does is surely just as important in assessing its desirability as its appearance?

  • Eran Tomer

    John – very good point, evolutionary history really does count. No question about Monito del monte (plus such an alliterative name to boot, “little monkey of the mountain”). Giraffe, Okapi, rhinos, elephants and equids are fascinating not in the least because they are the only surviving vestiges of formerly large and diverse families. This is also one reason their conservation is so vital. Should they vanish, we’d lose not only incredible species but entire branches of mammalian evolutionary lineage. It’s depressing enough to think about related species lost during the Pleistocene extinctions.

    Vladimir – great information, thank you ! You are a true naturalist and man of science to retain this perspective. Milennia of association with humans would make one forget the original House Mouse and rat populations. These rodents are also interesting by virtue of their social behavior, ecological plasticity and rarely-acknowledged intelligence. They are charming little animals, much as we wouldn’t want them inside our homes except as pets. If compared to other mammalian species, though, they’d probably still end up on the bottom of many people’s desiderata lists. And for the time being at least, I’d rather avoid entering the giant Human Sherman Traps that some locations in SW Asia constitute…

    Steve – I agree entirely that behavior makes all the difference. I’d gently point out that this is the second bullet down in the list of non-visual merits: “Attractive behaviors (displays, playfulness, acrobatics etc.).” Perhaps I should have mentioned this more frequently in the rank descriptions. And living inland, I must say I’m jealous of your Striped Dolphins. But we do have River Otters here, which I rank highly for their endearing behavior.

    Thank you all,

    – Eran

  • Antee

    This list, with every mammal in the world, with their specific category, should be on this site with automatic counter for people to “tick off”.
    Who has the most points and a feautered top 10 list on front of the page…
    Just for fun 🙂

  • tomeslice

    I highly enjoyed reading your logic and the categories.
    I think that this is a very good basis. I think there could be more sub-categories, actually based on some criteria that you elaborated on but decided not to include.
    For instance: pattern.
    There could be an algorithm based on a series of questions, such as:
    Does it have a distinct pattern?
    if yes –> Is it of high contrast?
    –> Is it a dominant feature in the appearance of the animal?
    –>What percentage of the animal is covered by the pattern? (in increments of 10’s)

    That was just one example… But I can see many other logical questions. There are also statistical ways to rate the rarity of an animal based on how many camera-trapping nights it takes to see it, 1 in how many naturalists in the area (birders/mammal/herp watchers, etc.) see it, how inaccessible is the area to “travelers” (based on accommodations, number of visitors..) etc. This can make up for things like “size” because clearly the pygmy hippo would take over the hippo because of rarity. But had they been equally rare, I think the regular hippo would be even cooler.

    That’s my suggestion, anyway 🙂
    In general I could definitely relate to your categories, but I think many mammal watchers would disagree with things like Nilgai or common hippo ending up in the same category as clouded leopard, and long-tailed pangolin, or White Rhino ending up above these two.

    Also with all respect to the bisons (and I have much respect for them), I don’t see them in a category 2 classes above any of the aforementioned species, or any of the rare cats to be honest.

    I actually think that the “desirability” algorithm must somehow include rarity or effort required to see a species, just because if you look at the other thread (where we last talked) you wouldn’t find lion or bison on any of the “top” lists… nor cheetah nor southern right whale.

    But like I said, you’ve made some very good points and it’s an excellent basis! Maybe another thread would be to brain storm all the criteria that should go into the algorithm, and then sub-criterias, how to quantify all of them, and what “weight” they would each receive. But at the end of the day, for some people, until they see an Okapi it will remain at the very top of their list, regardless of the best algorithm we can come up with 🙂


  • Eran Tomer

    Hi Tomer,

    Thank you so much for the thoughtful and detailed reply. You raise many excellent points so there is much to address in replying.

    Regarding visual sub-categories, pattern analysis algorithms etc.: this is precisely what I attempted to do in early versions of the ranking scheme. It worked well for describing species’ visual complexity. That is, which species are more complexly or boldly patterned, and by what degree, versus others. But I discovered that visual complexity is not commensurate with visual appeal. Complexly-pigmented species usually had considerable allure, but some with simpler pigmentation did too (sometimes even more so). The same happened with coloration. Thus I discovered that physical appearance ought to be evaluated holistically, and this worked very well.

    Regarding trap nights, how many people have seen a species previously, geographic (in)accessibility and related metrics: these are certainly worthy considerations. I included several of these as non-visual merits to evaluate:

    * Geographic range is remote, very small, or difficult to access.
    * Species is difficult to locate and / or observe within its range & habitat.
    * Species is little known and little studied.

    Different people will ascribe different weights to these matters, which is perfectly fine. Species evaluation is inherently subjective, not absolute.

    But concerning specifics such as traps, nets, prevalence of sightings etc. – where would one obtain such information for each of the world’s approx. 5,500 mammalian species ? Such statistics are unavailable. But, we do know which species are more difficult to see, or have less accessible ranges, or are more observable, or are lesser known, versus other. This suffices for deciding how challenging a species is to see.

    Further, observability and abundance vary geographically. Species can be rare and elusive in certain places, but much more findable and observable in others. This makes range-wide assessment problematic.

    More generally, there is the SUPREMELY important issue of analytical cost-benefit. Or as it’s sometimes called, Analysis Paralysis. This is a major consideration in science, especially in field research which is usually labor-intensive. It is also prominent in conservation assessment. One could evaluate species by very many parameters, each with complex algorithms and formulas and data-hungry criteria. This has the appeal of objectivity and precision. But the more complicated the process and the more data it requires, the slower, less efficient and more difficult the assessment. Also, the more problem-prone the method becomes. It’s easy to end up with an “overkill” – a process so tedious, inefficient and complicated that it defeats the purpose, or goal. Therefore it is imperative to choose the simplest, most efficient method that will produce the desired results.

    Simple example: suppose we want to assess the abundance of species in a certain area. We could conduct a labor-intensive, expensive, complicated study to derive the exact population densities of various species. For rarer species – as many are at any given area – this would require a *tremendous* amount of effort for procedural and statistical reasons. BUT, why are we assessing abundance in the first place ? Do we really need precise population density data, or are we just trying to answer the question, “Which species occur here ?”. In the latter case we only need an index of abundance, i.e. determine which species are more common vs. others, not exact counts of individuals. This greatly reduces the requisite effort and costs.

    This is exactly the reason that the ranking scheme started out exceedingly detailed and complicated and mathematical in the 1990s, then evolved into a more general and flexible format over the years.

    Regarding the importance of rarity and difficulty of seeing a species: these are always important considerations but different people ascribe different weights to them. Some folks are supremely lured by the challenge of finding rare or difficult-to-view or difficult-to-access species, while others place more emphasis on the animal’s appearance or nature. Some rarely-seen, little-known species found in remote, unwelcoming or dangerous places are not much to look at. Other well-known, well-studied species found in readily accessible places are majestic, stunning animals.

    Hence I wrote, “Rank assignment is ultimately subjective… [but] one’s biases will be applied in a consistent, systematic manner”. If you are greatly attracted by challenging species, you will rate all challenging species more highly than similar but unchallenging ones. Hence you’d have consistency and the ranking system will work well. Comparing desiderata lists among different people would obviously be less consistent, but the ranking scheme is NOT meant to assign species universal, absolute desirability ratings. It is meant to help one decide on mammal-watching priorities and effort allocation. This is very important to keep in mind.

    Regarding the individual species you mentioned: when I put together the “possible examples” lists, I anticipated major disagreements. I also faced difficulties as I tried to put aside my personal biases – obviously, not always successfully. Hence I wrote, “possible” and emphasized that these lists are only meant to give an idea as to the abstract rank descriptions. Hopefully the disagreements will generate informative and helpful discussions about various animals and what makes them desirable, rather than engender arguments.

    Thank you again for the constructive criticism. I much appreciate the feedback.

    All the best,

    – Eran

  • kittykat23uk

    It’s an interesting read, glad to see that rabbits and hares are solidly middle of the table. They would be higher in my own personal ranking. Tomer makes some good points. Another point on desirability scale for me personally is any given target’s proximity to other desirable mammals.

    ETA: so what I would quite like to see is a way of ranking/identifying how to determine what destinations give the best bang for the buck in terms of mammal diversity and desirability. That would be really useful to me in working out priorities for my 1-2 mammal watching trips per year! 🙂


    While this is certainly an interesting and thought provoking post to be honest I think it highlights the problems in trying to apply a scientific approach to something that fundamentally isn’t scientific at all. It’s about what excites an individual and gives them an adrenaline rush. To my eyes a lot of species listed as examples in ranks 6 and 7 are far more desirable than some of the examples given for rank 9 because it’s a personal preference. Although I doubt that many people would admit to agreeing with me even when they do, and others will most certainly disagree with me, having Homo sapiens, even ones spouse and children, as top of the pile is extremely odd even if it is true that in terms of capital expenditure they are more costly than seeing any other mammal on earth. As a well-known regular contributor to this site said to me yesterday ‘spouses come and go ….. but a Giant Panda sighting stays with you forever’. I’d rank many human beings right at the bottom of the desirability stakes myself. To think on this basis Donald Trump would be be the most desirable mammal on the planet to some people. What a thought!

  • Eran Tomer


    I feel that the ranking scale, and the idea behind it, are widely misunderstood. I’d like to clarify some of the points raised.

    Richard – the ranking scheme is not at all scientific, but systematic. Not math-and-science, simply organization. There is no question that ranking species’ desirability is subjective. But with about 5,500 mammalian species, and considering that field trips require time and money investments, how does one decide on priorities and resource allocation ? Of course it’s all about “what excites you” but how do you determine what species excite you more than others ? What makes a species exciting to a person ?

    The ranking scheme is designed to help here by enabling a person to arrange species by PERSONAL preference based on various criteria, not mathematical formulas. Again – not science, but organization.

    There is no science to spending one’s time and money either, but people have temporal and financial budgets based on preferences and criteria. We don’t spend time and money randomly. And it helps tremendously to be organized about it. (Hence the numerous websites that provide advice on this).

    As for Homo sapiens, so much for humor…

    Many folks take issue with the “possible examples” species listed for each rank. Please remember the key word, POSSIBLE. Rank descriptions are abstract so I tried to pick some suggestions that might illustrate what they mean. That’s NOT to say, “These species have, or ought to have, this rank”. Rather, read the rank description and decide for yourself what species qualify. And since you have your personal preferences, you will apply them across the board. Please don’t misunderstand the idea here and do pay attention to the text:

    “The ranks are meant as guidelines, not absolute rules. Rank assignment is ultimately subjective… The idea is that using the following scheme, one’s biases will be applied in a consistent, systematic manner. The subjective evaluations will be standardized.”

    “Read and decide which rank best describes a given species in your view”

    “Please recall that these categories are only guidelines and all the possible examples are meant as illustrations. Feel free to evaluate species based on your personal preferences but with these ranks, you’d have a systematic method to it”

    Also, an observation: most of the disagreements revolve around the highly desirable and specialized species mentioned under ranks 7-9. There seems to be less dispute about “average” and “below average” species. But Vladimir Dinets had the opposite perspective and focused on the lowest species mentioned which, in my opinion, was very astute.

    Tomer – regarding, “for some people, until they see an Okapi it will remain at the very top of their list, regardless of the best algorithm we can come up with”. This is precisely what Rank 10 is all about !
    “It encompasses one’s top picks… for the title, “World’s Best Mammals”. No need to discuss visual or non-visual merits as this is strictly a matter of personal choice. These species are at the very top of one’s wish list.”

    Finally, about the algorithmic / formulaic approach vs. the holistic approach to describing appearance. **Please skip this if not interested**. Consider how detailed algorithmic parameters can get.

    Example: horns / antlers – does a species have them ? If so, how many ? (Remember Four-horned Antelope). Length ? Ratio of horn length to body length ? Width ? Spacing ? (horns on side of head like Gaur, or straight up like an oryx, or intermediate ?) Furcation ? If so, how many branches ? Curvature ? If so, what angle ? Spiraling ? If so, how tight ? And how many coils ? Color ? Texture ? If so, how embossed ? (need scale). And on.

    Example: tail – what type ? (normal, cetacean fluke, uropatagium, others) Length ? Width ? Thickness ? Tail-to-body ratio ? Furry, hairy, scaly or naked ? Hair or scale density ? Tail prehensile ? Tuft on the end ? Color ? Color different from body color ? Curved ? (e.g. kangaroo) If so, what angle ? And on.

    Same for ears, legs and everything else. With colors and patterns this can get insanely complex so I won’t even attempt to provide an example. The question is, What would we gain with all this labor-intensive analysis ? If we were conducting a scientific, morphological study, we’d have to do it. But for determining a species’ desirability or attractiveness, we don’t need to analyze appearance in such painstaking detail. General gradations suffice, as noted in the ranking scale.

    Best regards,

    – Eran

  • Vladimir Dinets

    The problem I have with this approach is that it tends to further concentrate interest on the so-called “charismatic” species while drawing attention away from neglected ones. What is so great about birdwatching is that it makes people notice all those rare, localized birds nobody would care about otherwise. I so hope that the rising popularity of mammalwatching will finally create awareness of the scores of small, little-known mammals that slowly go extinct worldwide.

    Also, there is no such thing as a boring mammal. Once you learn more about (for example) voles biology, you will appreciate their ability to evolve high species diversity in areas where no other mammals have managed to do so, and the subtle but fascinating differences in natural history between voles that look virtually identical. Finding a lifer vole and watching it for a while will be a much better experience than seeing yet another cat run away from your flashlight for 0.05 seconds.

  • Eran Tomer

    This issue is intrinsic to the goal, not the method. If species are prioritized or ranked, no matter how and why, some will end up above others. Then the focus will be on the high-rankers while the low-rankers will be neglected.

    Now, I couldn’t agree more that there is no such thing as a boring mammal, or bird, or any species. Hence I wrote under rank 1, “no species is worthless”. It is this intense fascination with all life forms that propelled me, like numerous others, to study zoology / ecology academically and otherwise become a life-long naturalist and birdwatcher. Heck, even protozoans are incredible, let alone many invertebrates, fish, herps and “lowly” mammals. (Incidentally, I particularly adore rodents, shrews and other little furballs).

    Still, probably all mammal-watchers, birdwatchers, zoologists, ecologists and ethologists would find some species more interesting and appealing than others. That’s why mammalogists study mammals and not birds, and why some of them study voles, not elephants. Further, both scientific and non-scientific pursuits of wild organisms suffer from a chronic dearth of time, money and resources. Thus there *is* a need for effort prioritization by species – in science, in conservation, and in mammal-watching. That is, a need for organization and consistency as one approaches wildlife study. This is the idea behind the ranking scale, while the inherent problem of charismatic species bias is readily acknowledged.

    Mammals are some of the most challenging vertebrates to observe. And generally, the smaller the species, the more difficult it is to see (outside of traps). Hence it is an uphill struggle to promote smaller species and raise awareness of their biology, beauty, charm and conservation plight. This website helps greatly. Perhaps we should start a new thread on how to observe and promote small mammals.

    Best regards,

    – Eran

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