A Long Winter’s Nap: How Do Box Turtles Know When to Emerge in Spring?

Many of our local reptiles have evolved ways for dealing with cold weather. Eastern box turtles hibernate or brumate in burrows which they excavate in soft soil. Here they spend the cold months in a state of dormancy using as little energy as possible. Box turtles are freeze tolerant; they are the largest vertebrate that can withstand icing of their internal organs (for a short period of time).

We think we know what triggers brumation in the fall: air and soil temperatures and length of day each plays a role. But what are the cues that cause turtles to emerge in the spring, especially since light rarely penetrates the burrow?

I wanted to see for myself so I designed a brumation study around two radio tagged box turtles here at the sanctuary to see just how soil temperature affects their entering and exiting brumation.

Data loggers for recording soil and air temperature at two box turtle brumation sites in the winter of 2018.

The plan would be to closely monitor each turtle as the weather got colder and note when the animal entered brumation. At that time I would place an electronic temperature data logger in the burrow with the turtle as well as an identical control logger at the surface to monitor ambient temperature. I programmed the loggers to record temperature every 4 hours. My guess was that the soil temp would fluctuate with air temperature.

The two turtles that I chose are resident turtles who typically brumate at opposite ends of the sanctuary in different habitats. One brumates in the woods while the other overwinters in successional habitat between the woods and the heath field. Both are older adult turtles; #63 is a big female while #348 is an average size male.

You can just barely see turtle # 63 as she begins to dig her burrow. The gray device on her shell is a radio tag so she can be found.

The female entered her brumation burrow on November 1 with the ambient temp at 44 degrees and the soil temperature at 58 degrees. She rested at a depth of 5 centimeters for most of winter, which is somewhat shallow (average brumation depth is about 10 cm). Would she survive our exceptionally cold winter?

Volunteer researcher Tim O’Brien measures turtle burrow depth. (photo by Kim Novino)

I checked both turtles every couple of weeks and noted their positions within their burrows monthly by reaching in and touching them. The female stayed in her burrow for 178 days. She saw an average ground temp of 42.1 degrees and a minimum temperature of 33.0 degrees (January 4th).  On April 26, she emerged.  The air temperature at the burrow on that date was 53 degrees and the soil temp was 50 degrees.

 

Still a bit sandy from her winter’s rest, turtle # 63 welcomes spring.

The male entered brumation on November 26, fairly late in the season yet typical for this turtle.

 

Turtle # 348 begins his winter dig.

On that date the air temp was 40 degrees and the soil temp was 50. He eventually rested 18 cm below the surface which is fairly deep for a box turtle. He brumated for 161 days.

 

Data logger records air and soil temperature at a turtle burrow.

# 348’s average ground temperature was 42.2 degrees and he saw a minimum ground temperature of 34.9 degrees (January 8th). He emerged sometime between May 2 and May 4. The ambient temperature on May 3 was 57 degrees and the soil temp on May 2  was 50 degrees.

Turtle # 348 emerges in early May.

So what did we learn? It appears based on our very small sample size that both turtles, brumating at different locations and at different depths, saw nearly identical average soil temperatures throughout their brumation. I also found it interesting that each turtle emerged when the soil temp in its burrow hit 50 degrees. Also each turtle experienced a nearly identical minimum temperature which was just above freezing.

So is 50 degree soil temperature the trigger that causes box turtles to emerge in the spring? Also, do they seek a depth in the soil that will allow them to rest comfortably in temperatures ranging from the low to mid-40s and avoid freezing temperatures? I plan to monitor a larger sample size of turtles on the sanctuary this winter to see if we can answer some of these questions.

Tim O’Brien can often be found in this pose in late autumn at Wellfleet Bay. (photo by Kim Novino)

This post was contributed by turtle volunteer Tim O’Brien, who, when he isn’t studying box turtles at the sanctuary, can be found transporting injured box turtles and diamondback terrapins to Tufts Wildlife Clinic at the Cummings School of Veterinary Medicine in Grafton. He and his wife Kim Novino also rescue cold-stunned sea turtles in the fall.

23 thoughts on “A Long Winter’s Nap: How Do Box Turtles Know When to Emerge in Spring?

  1. Misty

    We have a male ornate box turtle that was given to us this spring. He spent the summer enjoying a large garden bed area. We had planned to bring him inside for the winter as our Colorado (Denver area) temperatures can get pretty cold in the winter. However, we were surprised that he has already dug in under a small bush and hasn’t emerged for a week. We’re still having day time temperatures in the 80’s (unusually warm for us) and lows in the 50s. We’re thinking we should try and dig him up and bring him inside. I wish there was a way to allow him to brumate without being too cold. What do you suggest?

    Reply
    1. Wellfleet Bay Post author

      Hi Misty:

      It’s a bit difficult to answer your question accurately without knowing more about the turtle, where it came from, it’s general health, was it wild caught or captive raised, etc. Also box turtles will burrow in slightly to escape hot temps as well. You mention that Denver is experiencing some hot weather now, so your turtle may be burrowing now to escape the heat. The safest thing to do for the turtle would be to bring it inside for the winter. They are quite particular about where they brumate, and if this turtle is restricted to a pen or other enclosure outside, the substrate there may not be suitable for over wintering. You should also have the turtle examined by a reptile veterinarian. Box turtles do not make good pets as they have very specific diet and housing requirements in order to stay healthy. If you are not familiar with what these are, you should consider passing the turtle onto someone who is.

      I hope you found this somewhat helpful.

      Best regards,
      Tim

      Reply
  2. Danita

    I live in Albuquerque. NM and have had 3 box turtles for a few years now. This is would be my third summer with them. Last year I had spotted all three by May 31. This year, I haven’t seen one yet. I have a lot of ground cover and not sure exactly where they burrow. One is in an area that sidewalk rain drains into at a slope, so I am worried they may have froze this year as we have rain storms this year and freezing temperatures into April. I an so sad as I am very worried that none of them made it. Is it possible they are just very late to emerge? The other thought I had is I do have a pine tree, that shed a lot of pine needles into the ground cover as well and hoping the ph did not get out of range for them either. I am still hopeful and will remain so.
    Signed Concerned turtle lover.

    Reply
    1. Wellfleet Bay Post author

      Hello Danita:

      You don’t mention what species of box turtle you have or whether or not they are wild or pets. If your turtles were healthy going into brumation, then they should have emerged by now. If I assume that they are wild, I can tell you that box turtles will not always brumate in the same area, even after years of doing so. So it may be that your turtles have simply moved on. I don’t think soil pH would have much to do with where your turtles choose to spend the winter. Box turtles like slightly acidic soil, so your decomposing pine needles should pose no threat. And let’s not forget that box turtles are very good at hiding; you just may have not seen them yet. Good luck and please let me know if they appear.

      All the best, Tim O’Brien

      Reply
    2. Wellfleet Bay Post author

      Hello Danita:

      You don’t mention what species of box turtle you have or whether or not they are wild or pets. If your turtles were healthy going into brumation, then they should have emerged by now. If I assume that they are wild, I can tell you that box turtles will not always brumate in the same area, even after years of doing so. So it may be that your turtles have simply moved on. I don’t think soil pH would have much to do with where your turtles choose to spend the winter. Box turtles like slightly acidic soil, so your decomposing pine needles should pose no threat. And let’s not forget that box turtles are very good at hiding; you just may have not seen them yet. Good luck and please let me know if they appear.

      All the best, Tim O’Brien

      Reply
    3. Dr. Japa Khalsa

      Hi Danita! Did your turtles come out? I live in NM and just rescued someone else’s pet box turtle that came out of brumination late and then I think he got lost. I am hoping that your turtles are OK because we did have a very cold Spring.

      Reply
  3. Stefan Kabir

    I just found a crate turtle lying along a rivulet bed. He was exactly at the dirt surface, no tunneling. I covered him with leaves and checked it with a stick. It is 28 degrees here today. Is it accurate to say that he will endure?

    Reply
    1. Wellfleet Bay Post author

      Hi, Stefan– Where are you located? Somewhere that’s pretty cold in June! Any turtle above ground under those conditions would be at risk if it’s still alive. Let me know your location and I’ll pass your question along to Tim O’Brien for his take. Thanks!

      Reply
  4. Sherry

    There is a eastern box turtle that i saw last yr. Really pretty. I came across same turtle the other day. Well he/she has been in same spot in woods for 3 days now. I am concerned. I picked up and it hissed and legs are limp. Head droopy at 1st but picks it up. There is a white substance around eyes. One eye will not even open. Legs look really thin also. Our night temps here in North eastern NC have been chilly lately. The spot it has been in is in woods and sunlight barely shines in the spot it is in. I took water and a syringe and wet around mouth. No interest. Later i walked back with some collard leaves and broke up and placed in shallow water on a paper plate. The turtle had burrowed itself under dying and dried chickweed. What do I do if there is anything I can do to help. Googling hasn’t helped. Great article to btw and i appreciate any advice. Thanks

    Reply
    1. Wellfleet Bay Post author

      Hi, Sherry, So sorry to be late replying to your comment. We’ll pass it on to Tim, though things may have changed with your turtle in the last week. I’ll have a comment from him soon. Thank you!

      Reply
    2. Wellfleet Bay Post author

      Hi, Sherry,

      It sounds like you may have a sick turtle on your hands. I’d suggest that you contact your local wildlife officials, or possibly reach out to a local wildlife rehabilitator. A veterinarian with turtle experience would be a good resource as well. Good luck. Please let me know how you make out.

      Tim

      Reply
  5. Debra Greaves

    My box turtle lives indoors has been under the dirt and straw for 2mths now..we are in PNW..the house is warm shouldn’t she becoming out soon??

    Reply
  6. Jeanne

    Hi Ron

    I have a box turtle and keep her out side in the summer and usually pull her in in the Winter, she has never burrowed before, but this year has twice the first time I dug her up and she was pretty deep i keep her inside for a week and then put her back out on a really nice sunny day (70 degrees , i live in Florida) so my question is how does she survive with all the rain we are getting i am worried she could drown but don’t want to keep digging here up, as she seems determined to be outside.

    Reply
    1. Wellfleet Bay Post author

      Hi Jeanne:

      You don’t say what type of box turtle you have or how long you’ve had it. Generally speaking it is healthy for box turtles to brumate. Of course, this assumes a healthy animal with no physiological issues. The turtle should be allowed to cool naturally and gradually prior to entering into brumation. If your turtle burrows in and the substrate is acceptable, I’d let it be. Rain is not a problem providing the turtle is not in an area that completely floods and the soil drains well. Moist soil will actually help keep it hydrated. If you are still concerned you could look into brumating the turtle indoors, but I wouldn’t recommend this unless you have experience.

      I hope this helps, Tim

      Reply
  7. Raz Rasmussen

    Thanks for posting this detailed mini-study. I moved from Southern California to northern Puget Sound this year and was looking for info to make sure my 3 eastern box turtles were ok to have their winter burrows outside here now that temps are dropping to freezing. They’ve been under since early Nov., and dug in pretty deep. (They’re in a garden area enclosed by a deep stone wall, under a covered patio.) I guess we’re good since temps don’t normally get as cold as the Cape here. I lived in Falmouth for 6 years while I was a grad student at Woods Hole, so I know those 10 F days (usually New Year’s Eve!) I recognize the HOBO temp loggers — have used them in field work a lot. Now I wish I’d kept a few for my yard! Good luck with the turtle work.

    Reply
    1. Wellfleet Bay Post author

      Hi Raz:

      Thank you for your note. I think that your box turtles will be fine. As you mention the temps in the Puget Sound region are relatively mild and they have buried themselves early enough to avoid any potentially lethal temperature drops. Good job. And yes, we are all too familiar with those early winter 10 degree days here on the Cape. I’m not looking forward to that! Take care and best wishes for 2021.

      Tim

      Reply
  8. jim harvey

    I just stumbled upon a box turtle lying along a creek bed. He was just at the soil surface, no burrowing. I covered him with leaves and marked it with a stick. It is 28 degrees here today. Is he going to survive?

    Reply
    1. Wellfleet Bay Post author

      Hi Jim:

      Thank you for your note. It’s hard to answer your question conclusively without knowing where you are located, the weather forecast and the general health of the turtle. Here in New England I would say that a box turtle on the surface in mid December at 28 degrees F would be a problem; in Georgia or Florida maybe not so much. Keep in mind that soil temp is important as well. If air temp is 28 for a few hours and the soil temp is much warmer (as it would be in a southern location), the turtle might be OK. The turtle may also have a health issue that is preventing it from entering brumation that could only be evaluated by a veterinarian or wildlife rehabilitation professional. I think you did the right thing by covering it and marking the location. Keep an eye on it and if temps are expected to be around freezing for more than a few hours, you might reach out to your local wildlife authorities or reptile rehabilitation organization for a recommendation. Let me know how you make out.

      Tim

      Reply
  9. donna black

    Wonderful information. I’m involved with a box turtle project in Georgia where we just completed the hatching season. Thanks for the article of your study.

    Reply
  10. Wellfleet Bay Post author

    Hi Ron:

    Thank you for your kind words. The short answer is, yes, box turtles will often dig deeper to avoid frost. However, here on Cape Cod the ground in the woods where they brumate rarely freezes and when it does it’s only a centimeter or two. Many of our turtles brumate at a depth of only 3-5 cm and make out fine year after year.

    Tim

    Reply
  11. Mike Howlett

    Tim is a true friend to turtles. This post is full of great information and a glimpse at Tim’s love of turtles. I am proud to call hima friend.

    Mike H

    Reply
    1. Ron

      What a GREAT article.
      Thank you for your important work!
      I hope you have the opportunity to do the same study with a larger sample size.
      The frost maps for zone 7 suggest the ground freezes as much as 24 inches. Evidently that wasn’t the case during your trial.
      So your question is important: Will turtles dig down further to avoid freezing temps?

      Reply

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