Signs of life - part 2

Winter reveals the lives around us. Deer tracks lead to deer beds frozen in the snow. The early songs of chickadees and titmice ring out in the cold air with little competition while they dance among denuded branches. A longer-term record exists in the nests exposed by the lack of foliage. This is a good time of year to examine that record, not only because many are no longer shielded from view but because there are no parents around to scare from their nesting attempts.



The builders of some of these nests, such as the vireo nest above, deal with winter by avoiding it. We may think of the red-eyed vireo as a local bird, but evolutionarily it is a tropical species that breeds in our temperate forest, probably due at least in part to our abundant insect populations in the summer. The winter vireo lives a very different life in South America - flocking instead of defending territories, eating almost exclusively fruit instead of mostly insects. When the vireos arrive back in late April or May, they may use some bark strips from this nest to construct their new one, but they most likely will not use this nest again.

Most smaller birds don't regularly reuse nests, although large raptor nests may be reused year after year, not always by the builder. Great-horned owls in particular do not build their own structures, so they will occupy anything from a crow nest to a heron nest to a hawk nest. Cavity nests are one form of smaller nest which, being sturdy and safer than stick nests, are sometimes reused. For example, the cavity below may have been excavated by a chickadee, then reused by a titmouse or nuthatch. One of the benefits of observing nests in the summer is that there is a chance to answer such questions as who exactly used this nest or were the birds successful. However, there is the risk that if you continuously visit a nest, even if you don't scare the parents you may lead predators to the nest either by your actions or by the scent trail you leave behind.



Chickadees, titmice, and nuthatches can all easily be found in winter foraging flocks. Another species which is still around but more elusive are American robins. Many migrate farther south, but some take their chance on finding enough food to survive the northern winter. Like vireos, they change their behavior to become birds which wander in flocks and feed mostly on fruit. A couple of weeks ago a flock of robins descended on trees near my office, and I haven't encountered them since.



This nest, still shielded by evergreen needles, is a reminder of when robins were territorial and family-minded. The outside weave appears to be loosening, but the form is intact. Bird nests must be maintained throughout their use. As the winter progresses, wind, snow, and freezing rain take their toll. One robin nest I found had been reduced to just the inner mud cup. So maybe the best time to look at nests is next winter, soon after the leaves have fallen and the birds have transitioned into their winter lives.

(Note - it is illegal to collect bird nests without a permit. This is a good thing because even if someone says they collected the nest in winter, there's no way to verify that that is true.
Besides, nesting material may be reused even if nests are not.)

Keeping warm

It's been longer than a week since my last post - sorry about that. My job requires staring at a computer for 8 hours a day, so at home it can be blissful to completely ignore the laptop. The northeast was in the grips of arctic temperatures last week, therefore much of my time at home lately has been dominated by hauling in wood and feeding the fire. Some nights our task has been to keep the house over 60 degrees (F) warmer than our surroundings.

Snowshoeing through the woods with a freezing wind on my face, it occurred to me that my body was using metabolism and insulation to stay 90 degrees above the air temperature. Everything may be one in a spiritual sense, but life depends on staying separate. As well as temperature, we maintain specific balances of water and salts, not to mention organic chemicals, which are very different from the environments we inhabit.

Cold temperatures are a fact of winter which any organism must deal with to live here. Some avoid the stress by taking on a different difficult endeavor: migration. Others rely on food to stay warm and active, such as the ubiquitous gray squirrels and the chickadees that chatter as they forage in our spruce stand. Still others, such as many insects, wait out the winter. Insects are the most diverse group with this strategy, but they're not the only one. Frogs and toads hibernate underground and wood frogs even freeze completely, yet revive in the spring. They pack their cells with glucose to prevent ice crystals from damaging them while allowing ice to form between the cells. Toads stay under the frost line, which allows them to keep their bodies a few degrees above freezing. Unfortunately they sometimes hibernate in garden beds, and last spring I dug up a rather large, pale specimen (I didn't think to follow its fate at the time).

Some mammals can't count on finding enough of the right kind of food all winter. Chipmunks are larger than some migrating birds, but long-distance travel on the ground is too time-consuming and dangerous. Keeping warm is difficult with a tiny body even compared to other squirrels, so chipmunks burrow underground where they maintain a body temperature around 40 degrees Farenheit. For the energy they still require, the burrow is stocked with food hauled in the chippy's big cheeks - especially important in the unpredictable beginning of spring.

Another rodent whose green food stores poorly takes a different strategy. We no longer see roly-poly ground hogs grazing along the interstate. Instead they too are hibernating and making good use of all that fat to fast until the world is again dressed in green. Sometimes I wish I could do the same. But we can take one lesson from the ground hog in light of the recent holidays and frigid temperature - it's not necessarily a bad idea to add a few pounds for the winter.