A squirrel gathers acorns in a yard in Saco on Sept. 25, when squirrels are in full nest-building mode. Shawn Patrick Ouellette/Staff Photographer

I read your article on squirrel nests. We have a large oak tree and numerous squirrels in our yard. Every year the squirrels bite off twigs from the tree and carry them to a crotch where three large branches converge. They attempt to deposit the branches there but the branches fall to the ground in a pile at the base of the tree. The squirrels have never successfully built a nest in this particular spot but they keep trying, and they never use those fallen twigs, they bite off new ones. What’s wrong with our squirrels?

– Joel Eckhaus, South Portland

This is an interesting follow-up from my Dec. 27 column about squirrel nests. I’ll admit I don’t have an exact answer, but it is fun to ponder. As anyone who has dealt with rodent “problems” knows, they seem to have a one-track mind and not much can deter them from whatever their goal may be. I say “problems” – not specific to Joel’s example – as a reminder that we are so often the ones encroaching on squirrels, we should shoulder some of the blame and take responsibility for some of the changes that need to be made to accommodate rodents.

First, Joel mentions that the squirrels are biting off new branches each time – this is normal. When making their nests, or dreys, they’ll typically start with fresh branches that will make a stronger base. These green branches are going to be less brittle than dead and drier ones they will use later in construction, along with leaves for insulation. I can only guess that, in the mind of the squirrel, it knows that a freshly cut branch will make a good base, and so presumably any branch found on the ground is old and not as desirable for nest building. That would be projecting a pretty limited amount of knowledge into the mind of a squirrel, but is my best guess as to why it always clips new branches. Humans are really bad at measuring the intelligence of non-human species, so I won’t be surprised when we eventually learn of a much more elaborate and purposeful reason for this seemingly wasteful behavior.

The second part of Joel’s question is why this squirrel is such a broken record, continually trying this same spot over and over. The simple “if at first you don’t succeed, try, try, again” explanation seems too human to make sense for a squirrel. We might have the luxury of time to repeat a project, but a squirrel faces greater live threats with each minute wasted. As discussed in my previous column, squirrels go into full “nest building mode” in the late summer and fall, so perhaps when this mode is in overdrive they get too focused on a single spot, apparently fixating until resources become too scarce. I’ll bet the wasted effort is going toward a second or third drey being built, based on what I’ve seen in my backyard. My squirrels have a large drey in a white pine that is used daily, though they keep putting effort into a new nest in the narrow space between my roof and solar panels. They keep trying, and I keep discouraging them, but they try, try, try. Interestingly, this winter they are only coming back to my roof on warmer, less snow-covered days, apparently when surviving is easier, and they can try building out.

Red-bellied woodpeckers are among the bird species that have gone through a fairly rapid range expansion in the last few decades. AP photo

‘RARE’ SIGHTING? YOU’RE GETTING WARMER

A week and a half ago I spotted, on the ground under our feeder, a bird that didn’t look familiar to me. I keep binoculars right by me so I got a look at it. From all indications from my amateur eyes it was a wren. I’m mostly positive it was a Carolina wren … that exact rusty brown with a cream color chest … same slightly curved up large beak and same tail lifted up … wide white stripe on the side of his head. So here’s my question: are there any of our local birds or any other bird at all (other than the Bewick’s wren) that would have those wide white stripes and exact colors? I’d like to be sure I saw this Carolina wren; if it was a Carolina wren, they aren’t too common up this far. Any help would be appreciated.

– John Robinson, Old Orchard Beach

One of my favorite parts of the job is getting calls or emails from people when they have rare birds in their yard. There is nothing more exciting than spotting something unusual or seeing something for the first time. especially when you’ve seen it well, taken notes, and confirmed it in your field guide. Unfortunately, the birds don’t read the field guides, and even more importantly, the birds are changing faster than the field guides are being updated. So John’s guide might tell him a Carolina wren is rare, but that’s no longer the case. In fact, the two species that I probably hear about the most are red-bellied woodpeckers and Carolina wrens.

These are two species that have gone through a fairly rapid range expansion in the last few decades, which makes the range maps in most field guides obsolete. Most field guides from the 1980s will show the northern range of these two species barely reaching into New England. There were only a handful of records of these wrens in Maine prior to the 1950s, but since then they’ve marched northward, becoming established in southern coastal areas and spreading toward midcoast Maine and more suburban areas. The red-bellied woodpeckers were a little slower to spread, but now occupy a very similar area to that of the wren.

What’s causing these range expansions? One interesting explanation is climate change. Habitat changes and food availability are likely factors too, but a study published in 2014 examined museum specimens from across the Red-bellied woodpecker’s range, prior to their expansion. They found the birds followed “Bergmann’s Rule,” an ecogeographical principle that birds (and other animals) at more northern latitudes were larger and had greater mass than birds farther south. Since it is colder at these northern latitudes, having more mass is important for surviving. The study then looked at the woodpeckers’ mass in their new, more northerly range and found birds with less mass at more northern latitudes than before. The reason birds with lesser mass can occur farther north, if you believe in science, would be because the temperature has increased in that area. Birds like these wrens and woodpeckers are a sign — right in our backyards — of the warming planet.

Do you have a nature question for Doug? Email questions to ask@maineaudubon.org and visit maineaudubon.org to learn more about virtual and backyard birding, online classes and other programs about wildlife and habitat.