Good question.  I'm not really a birder but I know trees and with the roots frozen in the ground, that would make it not conducive to fluid dynamics.  So I'll have to do a bit of research.  Do you know the species of trees on which you're seeing the holes? 

Also are you sure the holes are in the ordered pattern made by sapsuckers because if the holes are random, or are constantly getting bigger, it may be a woodpecker. 

Hello Kally,

Sorry for the delay, after consulting with fellow master gardeners here is what I drafted yesterday (platform issues delayed further.)

Here's what we know from our searches. Generally, sapsuckers move to warmer more southern locations for the winter which can be as near as Kansas and as far as Mexico. But it's possible that some stay in Minnesota.

I was made aware of an older research paper that contained observational data about sapsucker feeding. In addition to sap, they were observed to feed on the phloem and cambium of trees. The guess is that at times when there is less sap harvesting, the deeper parts of the wound would afford some sustenance. Maybe what you have is sapsucker damage but the problem is that the research paper didn't have photographs of the cambium feeding damage done by sapsuckers so I don't really know if it looks like the damage in your photographs. The researchers actually spent hundreds of hours watching sapsucker activity and identified sap feeding when they saw wet beaks and wood feeding with they saw pieces hanging from beaks.

It could be incidental that there are sapsucker holes in some of the damaged areas that appear as stripped bark. Usually, I think of squirrels when there is stripped bark. Squirrels are known to use bark for nesting, getting at the sap and cambium of trees for food, and sometimes just to sharpen their teeth. It's been observed that a single squirrel will develop a taste for one particular tree to bite off small twigs and pull off bark. You would see a lot of the evidence on the ground around the tree in that case. But one of the master gardeners I consulted isn't sure the damage is typical of squirrel damage; i.e., lack of teeth marks.

Because some drilling has been done in dead wood, I and my colleague believe that may be the work of woodpeckers.

You are right to be concerned about this damage and I think it may require vigilance to see who or what is causing this damage. Here is some information about animal damage control that may be of help should you catch a squirrel in the act. This article also identifies other potential culprits such as rabbits, voles, and deer. Other than the previous link on sapsuckers that I sent in an earlier message, I don't know how you can prevent them from damaging your apple trees if you should actually catch them in the act.  Perhaps you could check with bird groups.

In the case of deer, they rub their antlers on tree bark and the damage is much larger in area. In one three day period, one deer girdled my young crab apple despite my constant replacement of the plastic tree guard to protect the bark. I guess he used his antler to hook it and yank it off. The tree died.

Here is a link to an observer of one rather late leaving sapsucker and how s/he tried to get sustenance and warmth on a cold December day.

I hope this helps.

Kally,

That's really interesting about the giraffes.  I suspect there are more trees and plants that do the same thing. 

I like your approach, feeding the sapsuckers to keep them off your trees.  I don't know what will happen in the spring when tree sap is more available - if they'll resume feeding in the way they've always fed or stick with the suet.  Maybe contacting a birding organization would help.

Good-luck!