Do Reptiles Hibernate or Brumate?

Nearly everyone knows what hibernation means, but when speaking of reptiles the term brumation seems to reign supreme.  Why? Is one term more correct than the other?  To try make sense of these competing terms, I recently did some digging into the history of the word brumation which brought me to the following conclusions:

1. The term brumation is (mostly) unnecessary jargon.
2. Both hibernation and brumation should be acceptable terms to use in most (if not all) situations, however hibernation is the better term to use in a public forum.

As for why I've arrived at these conclusions, we need to look back a few decades to see where this word "brumation" came from, what we knew about hibernation way back then, and what we've learned about since.

If you happen to call that thing that snakes do each winter "hibernating" in front of an avid snake enthusiast, what usually follows is debate over whether the proper term is hibernate or brumate.  Often, the rational for using the latter is that reptiles spend the winter in a different physiological state than mammals (i.e. somewhat awake instead of unconscious) which therefore necessitates a new term to make the distinction. So where does all this come from?

Searching online journal articles for the word "brumation" leads to an article by Wilber W. Mayhew (1965) on hibernation in horned lizards (see below for references).  The final point of the abstract reads...

The term brumation is proposed to indicate winter dormancy in ectothermic vertebrates that demonstrate physiological changes which are independent of body temperature.

Searching for journal articles including the word "brumation" from 1965-1975 validates Mayhew (1965) as the origin of the term, as these later references usually cite Mayhew (1968) as the source. In the final paragraph of that article, Mayhew gives is a more clear version of his intended meaning of the word (emphasis mine):

Results to date show that relatively complex physiological changes occur during or immediately preceding winter dormancy in some ectothermic vertebrates. To this extent, these animals are similar to hibernating birds and mammals. However, they differ from these heterotherms (see Cowles, 1962) in their inability to control their body temperatures. Consequently, it seems advisable to have one term to designate winter dormancy in heterotherms and another for such ectotherms. Hibernation has been used to denote this condition in heterotherms particularly, so it seems best to retain this term for that group of vertebrates. Therefore, I propose the term brumation (from bruma, L. winter) to indicate winter dormancy in ectothermic vertebrates that demonstrate physiological changes which are independent of body temperature.

Clearly the term gained footing, but from the beginning some considered Mayhew's distinctions to be unnecessary.  They simply saw no real need for the new terminology, leaving those looking to keep abreast of the latest jargon wondering what they should be calling... you know... that thing reptiles do during winter.

As relevant today as they were a few decades ago, some authors were kind enough to share their concerns about this new terminology in their publications. So lets have a look at a few of these objections.

The early references I dug up simply equate the two terms. For example in Gatten (1978)...

In this paper, hibernation will be used in a broad sense to refer to the general reduction in activity in snapping turtles following cold-acclimation or cold-acclimatization. As such, it is equivalent to the term "brumation" as originated by Mayhew (1965).

The two terms were equated elsewhere (e.g. Dunham 1980, Bauwens 1981) although some took it a step further and took issue with Mayhew's original definition of the term.

One early example comes from Ultsch (1989), who basically gives the term brumation a pretty solid beatdown (emphasis mine):

There has been some concern, particularly among physiologists, about using the term ‘hibernation ’ to denote the state of ectotherms during the winter. The argument is that the term should be reserved for the state of controlled torpor typical of ‘true’ mammalian hibernators, with body temperature regulated at a low level at which the animal is torpid, and with arousal characterized by an energetically expensive and relatively rapid increase in body temperature to its normal operative range. Any other pattern, it is argued, is something other than hibernation and should be given another name. In particular, cold ectotherms, although their activity and responsiveness are often greatly reduced, are usually not torpid, their body temperature is close to or at that of their microenvironment, and they do not warm themselves endogenously during arousal. Hence a variety of other terms have been used to describe the condition of wintering ectotherms ; dormancy, cold torpidity, overwintering, and brumation (Mayhew, 1965) are among them.

Hibernation is derived from the Latin for wintering quarters, and to hibernate therefore simply means to spend the winter in sequestration ; there is no implication in the etymology about the physiological state of the animal. As such, hibernation is a general term applicable to all animals that seek a local refuge (a hibernaculum) in which to overwinter. Attempts to restrict its use to mammals may be mostly a reflection of the fact that most of the early and extensive physiological studies were done with that taxon. I see no pressing reason to develop an array of jargon concerning the physiology of overwintering. Therefore ‘hibernation’ will be used throughout this review, with the understanding that hibernation strategies vary among and within taxa. ‘Overwintering’ is viewed as a more general term that means only what animals do in passing the winter; possible strategies include remaining active, migration and hibernation.

There are two fantastic points here that deserve reiteration:

1. The term hibernation asserts no specifics about the physiological details of the hibernating organism.
2. One can use the term hibernation while recognizing that the underlying details vary among and within taxa.

Why is this important? Because in reality, there really is a lot of variation in how different organisms deal with shutting down during winter.  You can read more about them here, here, here, here, here, here and here.  Using the term "brumation" implies that reptiles have some special way of doing this, and that interpretation of the term runs the risk of whitewashing over a lot of that variation. That is, to some it gives the false notion that we have all the details worked out and summarized nicely by these two categories.

Here's my advice: upwards of 99% of the time you should use the term hibernate/hibernation, although if someone else uses brumate/brumation (appropriatly) you probably shouldn't bother trying to correct them.  Both terms suffice to get the point across, although hibernate/hibernation makes sense to a much wider audience making it the more appropriate choice in a public forum.

References

1. Mayhew, Wilber W. 1965. Hibernation in the Horned Lizard, Phrynosoma m'calli. Comparative Biochemical Physiology. Vol 16, pp. 103-119. doi: 10.1016/0010-406X(65)90167-2
2. Gatten Jr., Robert E.  1978. Aerobic metabolism in snapping turtles, Chelydra serpentina, after thermal acclimation. Comparative Biochemistry and Physiology Part A: Physiology. 61(2), pp. 325-337. doi: 10.1016/0300-9629(78)90116-0 
3. Dunham, Arthur E. 1980. An Experimental Study of Interspecific Competition Between the Iguanid Lizards Sceloporus Merriami and Urosaurus Ornatus. Ecological Monographs 50(3), pp. 309-330. (JSTOR)
4. Bauwens, Dirk. 1981. Survivorship during Hibernation in the European Common Lizard, Lacerta vivipara. Copeia 3 (Aug), pp714-744. (JSTOR)
5. Ultsch, Gordon R. 1989. Ecology and Physiology of Hibernation and Overwintering Among Freshwater Fishes, Turtles, and Snakes. Biological Reviews 64(4), pp. 435-515. doi:10.1111/j.1469-185X.1989.tb00683.x