THE NATURALIST’S NOTEBOOK: Cold fish and icy insects
How does a change in temperature impact nature?
Poor naked wretches, whereso’er you are,
That bide the pelting of this pitiless storm,
How shall your houseless heads and unfed sides,
Your loop’d and window’d raggedness, defend you
From seasons such as these?
—King Lear, Act 3, Scene 4
For the past two weeks, Americans have shivered and commiserated with each other as ludicrously cold temperatures descended upon most of the country. Four degrees in New York City. Negative forty in Minnesota. Skating in South Carolina. Did all the animals in the country just die of cold?
Nope. Wild animals are used to surviving a brief cold spell, even if we humans aren’t. Mammals find shelter, or burrow into the snow and stay warm that way. Birds fluff up their feathers for more insulation. Many insects, as well as the wood frog, have the ability to freeze solid with no ill effects. (You can do this at home by pumping most of the water out of your cells and replacing it with glycerin.)
Forestry experts are hopeful, however, that the polar vortex has slowed the spread of exotic pests. The emerald ash borer is an iridescent green beetle with cute, goggle eyes that has decimated the population of ash trees in Massachusetts. The woolly adelgid, resembling a tiny piece of white fluff, sucks the juices out of hemlocks. Both the borer and the adelgid are from Asia, and are susceptible to extreme cold in ways that native species are not. Recent winters haven’t been cold enough to kill them off, but this year there is a chance that their populations will go down. In addition, there will probably also be a decline in those nasty deer ticks that carry Lyme disease. Though ticks are native to New England, they do die if you deep-freeze them.
Our recent cold spell was relatively brief. What happens if the entire winter is cold? In that case, some small ponds remain frozen for so long that fish die for lack of oxygen. This is bad for fish, but can be great for frogs and dragonflies, which are eaten by fish. A colder winter can also mean more snow on the ground. This favors animals such as mice, which make tunnels in the snow to hide from predators. Deer, however, have a harder time finding food, and their long legs make it difficult to wade through deep snowdrifts. Once spring arrives, more snow means more meltwater, and so a cold winter leads to an abundance of spring flowers and foliage. The moral of the story: weather is complicated and has far-reaching effects.
Animals have thermal limits, and if these limits are pushed too far, species are forced to relocate or go extinct. The fauna of New England has already changed significantly because of climate change. Chirpy gray birds called tufted titmice have appeared at birdfeeders and are chasing away other birds. A few years ago, the northern winters were too cold for them, but now they are making inroads into Canada. Southern butterflies like the giant swallowtail and zabulon skipper have become common here in the past few years, and once-common butterflies like the atlantis fritillary have grown rare. Plant species are moving too, but for lack of legs, they often cannot shift their ranges as fast as animals. And organisms that live on mountaintops are in big trouble, since they have nowhere colder to go.
In the ocean, herring and other fish are also moving north to follow the colder waters and the retreating arctic phytoplankton. As a consequence, countries such as Iceland are discovering that their waters are suddenly teeming with fish. On the other hand, herring have diminished in the waters around Alaska. Steller sea lions (which look like seals with ears) live in Alaska and used to eat herring. Now they have to eat pollock, which doesn’t seem like a problem, since there is a lot of pollock. But pollock doesn’t have as much oil as herring, so the sea lions can fill their stomachs and still not get enough calories. Recently, the population of sea lions has plummeted, and many scientists blame the “junk food” fish that replaced the nutritious herring.
It can be hard to understand the significance of small changes in temperature. When l read that temperatures have risen by 1.4 degrees since 1850, my first reaction is “That’s all? Why can’t the fish cope with being a bit warmer?” But then I remember that I rarely have to cope with the real temperature. Most of us humans live inside, and we have nice things like sweaters and air conditioners to keep our bodies at just the temperature we want. Fish don’t have sweaters.
Imagine what happens when you get into the shower and the water is a bit too hot or cold. If you’re like me, you dive for the knob or jump out of the shower. It seems like an eternity before the water is the right temperature, and then it is the most exquisite bliss. That’s because when you’re in the shower, you don’t have a sweater on and you can’t feel the AC. In short, you are dealing with the temperature of your surroundings. This is what fish have to do all the time! In fact, it’s even more extreme for them, because the water is inside them, as well as outside. It’s no wonder that the herring are moving north.
There are really two kinds of extreme weather: short-term and long-term. Some weather incidents are brief and spectacular, like a polar vortex where bad stuff happens very quickly and is also finished very quickly. You may have to rebuild your house after the tornado, but at least it will be sunny while you do it. Long-term weather patterns are less dramatic, but nonetheless powerful. People tend to focus on the day-to-day extremes, because that’s what we see most easily, and it makes for good news stories. From an ecological standpoint, however, there is significance both in the polar vortex and in the warming winter.