A Hole New Mystery to Consider

On my last trip to the Niobrara Valley Preserve, I photographed the bark of wildfire-killed pine trees in warm late day light.  I liked both the patterns and the color and was just trying to make some visually-interesting images.  As I was taking the photos, I saw numerous small holes in the trees but didn’t think much about them.  Holes in dead trees are not really unusual, after all.  Upon looking at the photos later, however, I noticed something intriguing – many of the holes seemed to have a funnel shape, or beveled edge, at the surface of the tree.


Tiny holes in the bark of a standing dead ponderosa pine tree killed by a 2012 wildfire.  The two near the center of the image have a funnel-shaped or beveled edge to them.  The Nature Conservancy’s Niobrara Valley Preserve, Nebraska.

I couldn’t come up with a good explanation for that beveling, so I did what I usually do when I can’t identify something – I sent the photos to people with more expertise and begged for help.  Ted MacRae was kind enough to respond that except for the flared ends, the perfectly round holes might have been created by adult pine sawyers (Monochamus spp.).  James Trager liked my speculation that perhaps something like a woodpecker might have chipped away at the holes, looking for an invertebrate meal, and added nuthatches and chickadees as other options.  But none of us have a good answer.

After hearing back from Ted and James, I looked more closely at other photos from that evening and noticed something else that might or might not be a useful clue.  Not only had the edges of some of the holes been chipped (?) away, but there were similar marks elsewhere on the bark.  I’m not sure if those are related to what happened around the margins of the holes or not.  In the photo below, look at the “pitting” – especially in the top left quarter of the image.

More holes in trees.

More holes in trees, along with tiny chipped or pitted marks, both around the insect(?) holes and elsewhere.

Is some creature (bird?  insect?  microbe?)  chipping away at the tree?  If so, why?  And is that creature chipping away at the edges of holes made by beetles too?  And if so, WHY?  Or, are the beveled edges of the round holes a separate phenomenon from the pitted surface of the bark elsewhere?

I guess it’s good for my brain’s health to ponder mysteries like this, and it’s fun to think through all the possibilities.  On the other hand, it would also be fun to KNOW WHAT THE HECK IS HAPPENING HERE, so if you have good theories – or even better, actual answers – please let me know!

I didn’t measure the holes, so I hesitate to give estimates of their size, but they were really small.  Maybe 3-4 mm across?  I didn’t give that info to Ted (but I should have), and I’m wondering now whether the holes were actually too small for pine sawyer beetles.


Surviving the Winter

This has been a difficult weather week for many people across the eastern half of North America.  Strong winter storms have dropped tremendous amounts of ice and snow, and extremely cold temperatures and strong winds have made it difficult and unsafe for people to be out and around.  We were on the western edge of this storm here at home, so just had strong winds and a little snow (though still enough to cancel school for two days).  While I was sitting inside my warm insulated house, watching the wind blow the snow around town, it was hard not to think about all the creatures who have survived weather like this for thousands of years – without any of the comforts we see as basic necessities.

Species that don’t migrate to warmer climates have a couple of choices for survival when temperatures drop.  First, they can either hibernate or enter some other form of dormancy for the majority of the winter.  Second, they can stay active and survive as best they can – usually losing much of the fat reserves they build up in the fall.  Third, they can hide away during bad weather and search for food when temperatures are more moderate.  Late last year, I wrote an article for NEBRASKAland magazine summarizing some of the specific winter survival strategies used by Nebraska animals.  If you’re interested in learning more, you can read the full article here.  Otherwise, here are a few short anectdotes you might find interesting…

Water boatman encased in ice in a prairie wetland.

Water boatman

Insects overwinter in a variety of life stages, including eggs, larvae, and adults.  Most enter some level of diapause (a rough equivalent of hibernation for insects) in order to survive.  Those insects that overwinter as adults typically try to find some shelter by burrowing underground or at least into leaf litter or other insulating matter.  Even there, many of them end up freezing solid, only to thaw out and resume life in the spring.  I found this water boatman near the frozen surface of a shallow prairie wetland.  According to several sources I’ve found, these and many other aquatic insects can remain at least somewhat active in the water beneath the ice for much of the winter, but if frozen, can simply thaw out and start swimming around again in the spring.

A surprisingly active leopard frog in a cold prairie stream. The Nature Conservancy's Platte River Prairies.

Leopard frog

Leopard frogs, according to the research I did for the magazine article, are supposed to hibernate on the bottom of ponds where the temperature stays above freezing.  They settle into the sediment at the bottom of a pond, but leave space around the sides of their body where their skin can extract oxygen from the water in sufficient quantities to survive the long winter.  Imagine my surprise, then, when I saw this leopard frog SWIMMING across the bottom of a shallow creek the other day in sub-freezing conditions.  Now, it wasn’t swimming very fast, but it was certainly swimming – not just drifting with the current.  I imagine the groundwater-fed stream was warm enough that it provided the same above-freezing temperatures frogs get from pond bottoms.  In fact, a stream probably has higher oxygen levels.  But still – there was ice along the edges of the stream, and when I saw it stop swimming, I was able to catch up with it and photograph it sitting underneath some of that ice.  It’s not a great image from a photographic standpoint, but tells a story.  I’m not really sure why it was swimming when I saw it (Was it disturbed by me walking by?  Did it get hit by something floating downstream? Does it have to move periodically to avoid getting buried by sediment?) but it gave me something intriguing to wonder about on a cold winter walk.

An oppossum poking around in the snow. The Nature Conservancy's Platte River Prairies.


The opossum is one of a large number of animals (especially mammals and birds) that fit into the “hybrid” strategy category.  During very cold stretches of weather, it stays hidden away in a burrow and has a lower-than-normal heart and breathing rate to conserve energy.  When temperatures warm to a certain point, however, it ventures out to forage and recharge its stores of energy.  This one was poking around in the snow by some tree piles we’d burned the day before, apparently looking for food – but probably also enjoying the little bit of heat still emanating from the remaining embers.  Judging from its uninsulated pink toes and nose, it sure doesn’t look like much of a snow creature (and they do often have ragged frostbitten ears by the end of a hard winter) but oppossums have been around long enough that it’s hard to argue with their success.

Black-capped chickadee in winter.

Black-capped chickadee

Ok, so a chickadee is not exactly a prairie species, but it is a good example of an animal that is known to use a strategy called “daily torpor”.  Chickadees can drop their body temperature a few degrees overnight to save precious calories from being burned during a period when they’re not planning to move around anyway.  Many other birds and small mammals are thought to employ the same strategy, but there’s not much data (that I could find) on the topic at this point.  It certainly makes a good deal of sense, although you’d want to be sure you were in a nice secure place before you dropped into any kind of torpor while owls and foxes were patrolling nearby.


Regardless of your personal strategy for getting through the winter, I hope you’re enjoying this one so far.  Groundhog day has passed, so depending upon your local “hognosticator” you may or may not have a lot more winter to look forward to.

I think I’ll enjoy myself a little daily torpor.