How squirrels make their nests

Squirrels get a bad rap in many places, but I won’t stand for them being dissed here, especially because I take care of the local ones. And, like all animals, when you see them regularly and close up, you learn a lot of cool biology.

In case you didn’t know, squirrels do build nests to protect their babies and to stay warm in winter; you may have seen them in the form of big balls of leaves up in the trees, which are more visible in winter. While some squirrels use treeholes, the construction of a leaf nest is quite intricate:

Leaf nests are constructed from various twigs, leaves, moss and other material. To start, twigs are loosely woven together to make up the floor of the nest. Next, squirrels create more stability by packing damp leaves and moss on top of the twig platform to reinforce the structure. Then a spherical frame is woven around the base, which creates the outer shell. The final touches include stuffing in leaves, moss, twigs and sometimes even paper to build up the outer shell of the new home.

The inner cavity of its leaf nest is about six to eight inches in diameter and lined with more material, usually shredded bark, grass and leaves. However, some squirrel species, including Gray Squirrels, can have nests that are much larger. Some nest cavities can span 2 feet wide!

squirrel-leafnest

Cross-section (I hope no squirrels were harmed in the making of this photo):

squirrel-dreyA few days ago the New York Times had a piece on nest construction; click to go to the article. I’ve put an excerpt below:

screen-shot-2017-01-31-at-11-28-30-am

The squirrel begins by roughly weaving a platform of live green twigs. On top of this, soft, compressible materials like moss and damp leaves are added. Then an outer skeleton of twigs and vines is built around the insulated core, and finally, additional material fills in and strengthens the shell.

For the familiar gray squirrel, Sciurus carolinensis, the central cavity is about six to eight inches across. Smaller species build proportionally smaller nests.

One study of nest materials used by European ground squirrels found that damp leaves and moss provided better insulation than dry lining materials.

A 2013 German hidden-camera study of a red squirrel filmed a nest being built in work periods totaling more than three and a half hours over three days. The squirrel carried material to the site with its mouth and front paws; bent stiffer twigs with its head and face; pushed other material into place with its legs; shredded lining components by holding them with the front paws and chewing; and shaped the inner cavity by lying in it and turning around.

These people got a ringside seat as a squirrel built its nest on a windowsill. Note the intricate weaving of twigs:

h/t: Mehul

 

36 Comments

  1. Mark Reaume
    Posted February 6, 2017 at 9:12 am | Permalink

    Interesting, I saw the NYT article the other day. I’m curious, do they learn these techniques from their parents or is this part of their ‘programming’?

    • gravelinspector-Aidan
      Posted February 6, 2017 at 3:17 pm | Permalink

      As sensorrea suggests below, squirrels seem to learn these techniques in the same way that people get relatively fair judiciaries : trial and error.

  2. sensorrhea
    Posted February 6, 2017 at 9:18 am | Permalink

    Last summer I began to find leaves and branches accumulating in my driveway in one particular area. I had no idea why. It was not Autumn and we hadn’t had any big wind events. I cleaned them up, but the next day there would be more. This mystery went on for almost a week until I noticed a squirrel up in the tree busily attempting – and failing – to build a next. It kept dropping the branches it was trying to weave together onto the driveway below. Eventually the rain of debris stopped. I guess it was smart enough to find a better place.

  3. Posted February 6, 2017 at 9:22 am | Permalink

    That’s very interesting, thanks for posting this.

  4. Angela
    Posted February 6, 2017 at 9:24 am | Permalink

    I take one of my cats, Leroy Jethro, outside on a leash. Watching squirrels is one of his favorite past times. The squirrels have been building their nests in the past few weeks and Leroy and I have both been watching in fascination. Of course, while my fascination is purely scientific his is completely predatory.

  5. eric
    Posted February 6, 2017 at 9:32 am | Permalink

    We have loads of them around our neighborhood. Though in our case it seems the squirrels build them fairly early compared to Angela’s area, as the leaves falling off the trees in Oct/Nov usually reveals a fair number of them already built.

  6. Mark Sturtevant
    Posted February 6, 2017 at 9:34 am | Permalink

    I have a couple of these in our Really Big Tree in the backyard. I have noted that they do not build nests in the various smaller trees, even though the branches are denser. Just the big one.

    • Randall Schenck
      Posted February 6, 2017 at 10:00 am | Permalink

      I would note the same. Squirrels tend to go high in the tree to build and the higher the better. Birds will build in small trees but not squirrels.

  7. Posted February 6, 2017 at 9:51 am | Permalink

    It amazes me how an animal so adept at building and finding and storing food can manage to become street pizza at almost every available opportunity.

    • Dominic
      Posted February 6, 2017 at 10:18 am | Permalink

      I am pretty sure that there is an inverse relationship between the busy nature of a road & the wildlife killed on it – the busy road deters animals & birds, the quieter the road, the more likely the creature is to be caught out.

    • eric
      Posted February 6, 2017 at 10:19 am | Permalink

      Its not so amazing. They developed adaptations to deal with winter and predators over the span of millions of years. Natural selection on behavioral adaptations for dealing with fast-moving cars has only been going on for about 100 years. A piffling amount of squirrel generations. Give it a few thousand years, I’m sure they’ll be supremely excellent car-avoiders. 🙂

      • Mark Sturtevant
        Posted February 6, 2017 at 12:25 pm | Permalink

        I go with that one. In comparison if you drive thru Oklahoma and Texas, you will see a good number of armadillo roadkills. Their evolved defense against predation is to either roll into a ball, or spring up a couple feet. Neither works well for cars.

        • Mark Reaume
          Posted February 6, 2017 at 12:30 pm | Permalink

          I also recall hearing that some birds are evolving smaller wings which improve maneuverability which helps to avoid becoming roadkill.

    • gravelinspector-Aidan
      Posted February 6, 2017 at 3:15 pm | Permalink

      become street pizza at almost every available opportunity.

      I can’t remember the name of the statistical fallacy you’re replicating, but it’s a well-known one. For each squirrel pizza that you measure, how do you tell the number of times when that particular (ex-) individual squirrel avoided becoming pizza?
      You have a coin which until today you believed to be “fair” ; you’ve flipped it 19 times today, and each time it has come up heads ; what is the probability of getting heads on the next flip?

      • Dale Franzwa
        Posted February 6, 2017 at 11:31 pm | Permalink

        50%, everybody should know that.

        • gravelinspector-Aidan
          Posted February 7, 2017 at 7:06 pm | Permalink

          “should”
          Not “does”.

  8. Randall Schenck
    Posted February 6, 2017 at 9:57 am | Permalink

    I loved watching the squirrel build their nest and do all kinds of things in the perfect environment where I lived. Big trees are the key and if the big trees also provide food like the Bur Oaks then it is better. Nests in the fall seem to appear almost overnight. Seeing the squirrels heading up the tree with a mouth full of stuff is a sure sign the building is on. Trees are everything to the squirrels and without them, we would have very few squirrels.

  9. Dominic
    Posted February 6, 2017 at 10:12 am | Permalink

    Actually it is NOT a nest – a squirrel makes a drey!

    • Dominic
      Posted February 6, 2017 at 10:16 am | Permalink

      I see the article says that in the first para 😉
      “The nimble Squirrell.. Her mossy Dray that makes.” 1627, Michael Drayton, Quest of Cynthia in Battaile Agincourt 141 (see OED online)

    • patrick
      Posted February 6, 2017 at 10:35 am | Permalink

      Thank you! I was about to comment on them being misnamed as nests.

    • Gregory Kusnick
      Posted February 6, 2017 at 12:42 pm | Permalink

      Wikipedia:

      A drey — or dray — is a nest of a tree squirrel or a flying squirrel.

      (My emphasis.)

  10. Joe
    Posted February 6, 2017 at 10:40 am | Permalink

    I used to like squirrels until one created a hole underneath my eave, and took to removing insulation from the space above my ceiling. Fortunately, the squirrel was not nesting there but it was quite noisy whenever it removed insulation. It must have a pretty cozy home somewhere …

    • patrick
      Posted February 6, 2017 at 11:20 am | Permalink

      I use to like the local red squirrel until I discovered the little bugger had packed my vehicles air vents full of walnuts.

      • Randall Schenck
        Posted February 6, 2017 at 11:41 am | Permalink

        Hate to say, but that is why they build garages. If you do not have one, get a cover.

        • Posted February 6, 2017 at 12:33 pm | Permalink

          Have to agree with you regarding garages. Most of my neighbours never use their double or triple garages they being too full of other “stuff” to get a motor vehicle under cover. We always garage both our cars during the winter and the benefits are too many to list. However on the subject of squirrel home lining, the under soft padding of our barbecue cover seems to be one favourite every year and we don’t object to this skillful use of local building materials as it means we see more red squirrels.

  11. Ann German
    Posted February 6, 2017 at 11:55 am | Permalink

    We have over 18″ of snow on the ground here in NW MT, and the squirrels (pine and grey) tunnel under it, popping up to look around at various outlets, or coming out to get into my “squirrel-proof” bird feeders. I have tried to photograph these sleek little passages, but there is little contrast so it is difficult.

    • Michael Fisher
      Posted February 6, 2017 at 12:55 pm | Permalink

      @Ann

      If your camera allows it try capturing in RAW format – there’s no compression & you can easily correct over/under exposed images in post-processing
      Also shooting at dusk/dawn under a clear blue sky helps oodles

  12. TJR
    Posted February 6, 2017 at 12:34 pm | Permalink

    Hmm, I’d always assumed all the nests you can see in the trees were birds, but it looks like the ones big enough to be really obvious from below might in fact be squirrels.

    Note to USers: the word “squirrel” is pronounced phonetically!

    • Jeremy Rigsby
      Posted February 6, 2017 at 4:32 pm | Permalink

      I’ve got a squirrel that’s built at least two different nests over two years in an rampantly overgrown but still pretty spindly blackberry bush just outside my bedroom window. Like only 3-4 metres off the ground.

      If I nap with the window open the squirrel often wakes me up. Apparently my snoring sufficiently resembles a squirrel threat/territorial vocalization, and the squirrel shrieks in reply. When that happens I always look out the window and glower. The look on the poor thing’s face when it realizes it’s been arguing with that damn giant monkey again is just priceless.

  13. Posted February 6, 2017 at 12:58 pm | Permalink

    Hm, I’ve seen something that looks like this, but the crows are always near it – so I had assumed it was a crownest. Maybe I was wrong.

  14. Kiwi Dave
    Posted February 6, 2017 at 2:45 pm | Permalink

    How do damp leaves provide better insulation? That seems quite counter-intuitive. The only explanation I can think of is that damp leaves might be more pliable and seal gaps better than stiff, dry leaves.

    • Michael Fisher
      Posted February 6, 2017 at 4:29 pm | Permalink

      Read the link in the post that’s labelled “One study” & it’s more or less in agreement with you

      Damp leaves don’t provide better insulation, but as you say they are more pliable & thus Mr. & Mrs. Squirrel can make a home with fewer gaps for wind & rain to penetrate. In the study the comparison was between fresh grass [not necessarily wet] & dry grass.

      I would suppose that the wet leaves have time to dry out since squirrels will build nests long before breeding & also they bring in dry materials to line the interior bottom.

      Squirrels live together in groups outside of breeding season & they will construct multiple drey nests/dens if they’ve recently moved into a fresh area without squirrels or if their list of 2nd, 3rd etc homes shrinks due to infestation, storm damage, being stolen by owls etc. – squirrels ain’t happy unless they have a few drey nests/dens about the place as backups [some of which may be left over from previous seasons], so they must become very smart at construction.

      This Wiki is interesting because it says different squirrel species employ different materials/techniques:
      https://en.wikipedia.org/wiki/Drey#Construction

  15. jeffery
    Posted February 6, 2017 at 9:59 pm | Permalink

    They’re cute and fun to watch outside, in trees, but I had to cut off all of the limbs that allowed access to my apt. house roof as they were determined to do the same thing in my attic and spend winter nights squabbling with each other- when wires started to get chewed through, it was time for those limbs to go! Once they have access to the eaves of an old building, they will never, EVER give up on continuing to try to get in, anymore than they’ll completely abandon attempts to access a feeder- after all; they’re squirrels; what else do they have to do?

  16. chrism
    Posted February 7, 2017 at 5:10 am | Permalink

    I’m used to seeing dreys made by grey squirrels (tough not where I live), but I have never spotted a drey belonging to the local red squirrels (Tamiasciurus hudsonicus). There are three that I feed (Jerry’s going to kill me but only as a poor substitute for my beloved chipmunks)and whilst I have spotted a hole that they go into in a dry stone wall – presumably a midden – I can’t see any drey. My acre of garden is mostly tall deciduous trees and their leaves are down, so I would expect to see them. I’m guessing they either are using holes in tree trunks, or maybe as an extreme cold adaptation sleep in their middens?

  17. chrism
    Posted February 7, 2017 at 5:10 am | Permalink

    though, obviously

  18. chrism
    Posted February 7, 2017 at 5:30 am | Permalink

    One further thought, the red squirrel in that video, though described in the paper as S.vulgaris, is the first one I’ve seen without ear tufts. It looked just like my squirrels, not the smaller european red with those gorgeous tufts:

    Perhaps it was a youngster.


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