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My rabbit is virtually fearless. He does not run from cats or running cars, showing curiosity instead. (The one time he got up close and sniffed a cat, he did become startled and put a couple meters of distance from it. And he does hop away from moving cars, but not as fast as he could.)

Issues of outdoor protection aside, my question is about the physiology of trancing. (I've only done this to check his teeth, by the way.)

When he's upside-down, he'll kick for a couple seconds before he rolls his eyes and passes out. After I put him back, he seems none the worse for wear. He goes right back to his usual friendly self. I thought this was normal until I saw "Can trancing a rabbit have cumulative negative effects?":

The immediate side-effects of coming out of TI include things like increased respiration, heart rate, and plasma corticosterone (a steroid found in many animals).

…

the response after release is to escape and hide which, after all, is the purpose of TI in the first place

My bunny is certainly uncomfortable with being upside-down, but seemingly no more than if he's picked up awkwardly. As for the rest, he just gets really sluggish. Is this unusual? It seems to conflict with the common explanation of tonic immobility.

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  • The things you learn coming to this site. I had a rabbit for 7 years, and I assumed he was just relaxing when I turned him upside down to trim his nails. Huh. Whole new perspective.
    – Coronus
    May 31, 2014 at 6:21
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    Good question in my answer here I address the science & relationship between trancing and fear. But which is the cause and which is the effect?
    – James Jenkins
    May 31, 2014 at 9:36
  • @JamesJenkins Thanks, if that answer were here I would select it. The key is that it varies by the individual. What my rabbit does isn't even well-described as "immobility"; he just gets very slow and weak but he's still blinking and squirming a little. And if his feet aren't kept well above his head he comes out of it immediately. I guess TI may be a combination of a head-rush reflex and a fear response, and my bunny lacks the latter.
    – Potatoswatter
    May 31, 2014 at 14:10
  • We can let the community decide if it is a dupe. While my answer there might be what you are looking for, Johns answer here addresses parts of your question not addressed there. I have created a trancing tag to facilitate finding these related questions.
    – James Jenkins
    Jun 2, 2014 at 11:52

1 Answer 1

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Tonic immobility is the ability of many prey animals to go into what appears to be a near-death state with the intention of encouraging the predator to release them from any escape preventing grip. The idea being that if they're released, they have another chance to escape from the predator.

Given the basis of the function is to increase their survival rate in a life/death situation, it would arguably suggest that the rabbit needs to be in a heightened state of fear to trigger the response. However, there a some studies that suggest that there a several factors involved in TI:

  • Pain response. Rabbits that were treated with a beta-endorphin (released by pain) blocker had reduced TI duration. This suggests the pain levels effect the duration which makes a lot of sense. Basically, if the goal is to get released by a predator, one of the ways that the body will determine success is a reduction in pain. It also implies that a certain level of pain is associated with triggering the response in the first place, but not necessarily.

  • Body temperature. There is some research to indicate that reduced body temperature, causing shivering, reduces the effect of TI and higher body temperature increases it. From a speculative point of view, a severely injured rabbit with significant blood loss may be past survivability and thus there is little likelihood that TI would save them. The blood loss would reduced their body temperature, potentially to the point that they can't enter TI.

  • Fear. There have been studies using fear stimuli to test the impact of these on the ability to engage in TI. The one I just linked to involves chickens, but the TI behaviour is seen across a number of species including frogs with similar results. Basically, the presence of a fear inducing situation, such as a predator, is likely to lead to TI as a means of escape or to encourage the predator to believe that they're not live prey. Many predators prefer live and so the effect can potential prevent an attack in the first place.

Long story short, there several factors involved in this, but fear does appear to play a very large role in this. Bear in mind that placing a rabbit on its back puts it in a very vulnerable position and removes many of their defensive and pretty much all of their offensive weapons, that has to be a bit fear inducing if nothing else.

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  • Hmm, this is similar to other info I've read. Still, as I mention in a comment above, my bunny has a very weak TI response. His pulse doesn't ever seem to change, and there are no other signs of fear… he'll just go right back to whatever he was doing before. So I'm still unconvinced. Not that I have any motivation to do this more than necessary.
    – Potatoswatter
    May 31, 2014 at 14:15
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    @Potatoswatter - I appreciate that you're operating from the view of your rabbit, but I'd suggest that this a little less scientific than other approaches. :) There are a ton of studies on this activity because it is so easily induced and provides valuable insight to many including psychologists and biologists. Bear in mind that response is not uniform, even within a species, and so this is why they use more than one animal. If it was uniform, then we would only need one.
    – Joanne C
    May 31, 2014 at 14:52

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