The Robins of February: Following the 37 Degree Isotherm to a New Climate

By Gary Berg-Cross

Heard this song in the morning? It’s a robin song. I woke up to that sound several days ago. Over a hot drink I had an avian voyeuristic morning watching waves of robins cleaning my back yard for worms.

Spring is not yet here in February, but the robins, harbingers of spring, are and you and track their path north at http://www.learner.org/jnorth/robin/index.html In late January they were in Roanoke VA and as far as Hauppauge NY. Our neighbors in Berryville VA reported seeing 2 of the birds on Feb 2^nd and a week later there were flocks of them in my neighborhood. By the 12^th they were seen in upstate NY.

To be sure robins and other birds have to be practical and opportunistic about getting food. If local conditions are favorable, such as soft rains to surface their wormy food, they may do well if the temperature dips a bit lower. This year more Robins than usual seem to have wintered over in our area and apparently they have found places as far north as Vermont as a tolerable enough place to spend the winter finding food on sunny hillside and warmth near houses ( report from Katja Bahnemann-Evans of Braintree, Vt.)

The sharp, clear air feels a but like early Spring. Many people have noted curious sign of an early Spring including folks in Michigan. Besides the robins it’s the house finches. In spring, the males turn a very purple/red color to strut their stuff for their bird girlfriends during mating season. In this February’s Michigan some males are starting to turn that sexy finch red. Then again in some places people report seeing streaks of eastern gray squirrels chasing each other up and down trees getting ready for an early mating season. It used to begin in mid-March. Now they are scampering in my yard with some bold ones lazily scratching in the sun on my deck.

This is all a bit unscientific but it did get me to dip a toe into a bit of the science. I learned something about the Spring movements of robins. They usually follow what is called the 37 degree isotherm. We are well above that, our recent low of 39 was higher than that. What such temperatures allow is what is called a "vertical migration" allowing the first
earthworms of the season. In the fall Earthworms migrate down into the earth to escape below the frostline. Research finds that they sometimes they ball up in wormy groups to reduce moisture loss. A ball may have as many as a hundred worms all bunched together and in this community they spend an inactive winter. But when the weather when drives frost from the soil, the earthworms become vertical migrants and tunneling upward and appear at the surface. A warm rain, of course, helps loosen the ground and you might have noticed we’ve had these along with high average temperatures that have left our ground reaches above 36 degrees. If you look at the WAPO weather page you can see this winter’s stats on “heating degree days” – an index of fuel consumption tell us by how many degrees the daily average fell below 65 degrees and thus required that degree of heating to be comfortable. By this time in February the historical total of such heating has been 2835. We had a cooler than normal winter last year and needed 2913 or some 80 degrees more of heating. This year our total is only 2330 and thus we’ve needed almost 500 degrees less of heating than normal. A measure of how deviant we and many other parts of the US have been.

What's happening is so noticeable in the last few years that scientists can track it from space. A few years ago Satellites measuring when land turns green found that spring "green-up" is arriving eight hours earlier every year on average since 1982 north of the Mason-Dixon line. These trends are showing up in the northern climes more than the south, and up north it affects what is called phenology or biological timing. The mutual timing of worms and robin arrival is one example. To a large extent biological spring is based on the tilt of the Earth as it circles the sun. But climate change seems to be having an influence and we need to better understand the changes, and what do they mean for humanity and our fellow creatures.

Back in 2008 people were talking about winners as well as losers in any change but we still are unsure of the range of ] effect that consistent global warming will have. It is like to confuse the natural coupled timing that evolution has provided. Sure we will appreciate savings from heating bills with milder winters and more bird songs. We and Canada will get a longer growing season and Maryland wines will be taste better.

But the sobering expectation is such things as a broader biological view that foresees big problems such as species to extinction. As with the robins and worms certain plants and animals are dependent on each other for food and shelter. In my garden some of the bulbs are up. If plants bud too early they are vulnerable to a late freeze from an arctic high and weather variability is one thing that may come with the early phases of climate change.

If the plants bloom or bear fruit before animals return or surface from hibernation, our animal friends and their young may not be able to cope and could starve. Tree swallow chicks are laying eggs 9-10 days earlier than in the 1960s in places like NY. They now starve if we have late cold snaps because insects stop flying in the cold, according to reports from ornithologists like University of Maryland biology professor David Inouye.

A more recent story notes:

"U.S. Forest Service researchers have confirmed what has long been suspected about a valuable tree in Alaska's Panhandle: Climate warming is killing off yellow cedar.


The mighty trees can live more than 1,000 years, resisting bugs and rot and even defending themselves against injury, but their shallow roots are vulnerable to freezing if soil is not insulated by snow. And for more than a century, with less snow on the ground, frozen roots have killed yellow cedar on nearly a half-million acres in southeast Alaska, plus another 123,000 acres in adjacent British Columbia. "

I’m enjoying the reset of nature’s clock to an early Spring and my earlier than usual birding and bulb blooms, but I do worry that it is all not just for the good.