Our globally warmed climate seems to be giving us winter in short bursts. Between the blizzards we have the sort of weather usually associated with late fall or early spring. This alteration of the seasons seems to be changing some well-established ecological patterns. Reports come in of short-eared owls apparently still flying south in January. The saw-whet owl reported at the Morton Arboretum is sticking to the traditional schedule. But along the lakefront gulls are on the move somewhat early, while the waterfowl I associate with the first stirrings of spring are showing up--sometimes in large numbers--well ahead of the usual time.
Thousands of mergansers, especially red-breasted mergansers, have been seen in the waters near Shedd Aquarium, among other places. Small flocks or single birds of these fish-eating ducks can usually be found on Lake Michigan throughout the winter, but I remember really big numbers being more likely in March and April than late January. Steve Mlodinow, author of Chicago Area Birds, seems to agree with me. His book shows the red-breasted merganser is uncommon until the end of February. After that its numbers increase until they peak in late March and April.
Further investigation took me to my own records for 1976 and 1977. In those days poor people were still allowed to live around Lincoln Park. We lived close enough to the lake for me to walk my dog almost every morning along the shore south of Belmont Harbor. Birders are obsessive about records, and my notes on those walks are probably intolerably slipshod by some standards. But they do offer a picture of a weather situation very different from now. And the change in the weather has had an interesting consequence.
Back then I saw mergansers pretty regularly throughout January and February, but the flocks of thousands didn't arrive until late March. The real difference between then and now is reflected in the amount of attention my notes devote to ice. I keep coming across entries like this one from January 21, 1977: "Lake nearly all frozen. In few open spots, 40-50 white-winged scoters; 2 red-breasted mergansers; 4 goldeneyes." The next day I wrote, "Flocks of white-winged scoters and a few goldeneyes in only two patches of open water visible."
By February 6, when the temperature registered nine degrees, I wrote simply, "Water all frozen. No birds." The next day the temperature went down to six, and my notes say, "Solid ice. No birds."
Ice is a pretty effective control of waterfowl. If they can't swim, they can't eat. In colder winters Lake Michigan--especially the nearshore areas--might be frozen solid on some days. On other days open water would be confined to small shifting places in the ice. Last Saturday, driving the Outer Drive from McCormick Place to Hollywood, I didn't see any ice at all. Diving ducks like mergansers or goldeneyes or white-winged scoters can land anywhere they want to. The shallow, nearshore waters that are their favored hunting grounds are all accessible.
Gull movements are probably similarly affected. Gulls are more scavengers than hunters, but lake ice would certainly cut them off from food sources.
And then there are the mountains of ice and snow that covered the beaches and other nearshore land areas. We have a little of that this year from the big storm, but nowhere near what we have seen in colder winters.
We have also seen a major change in gull populations in the past 25 years. When I was birding the lakefront 25 years ago herring gulls were the birds we expected to see in January. We might find a few ring-billed gulls, but they were uncommon until the end of February. The success of the gull nesting colony at Lake Calumet has changed that. The thousands of ring-billed gulls that nest there every year create a large, year-round population. In many supermarket parking lots these birds are as common as pigeons.
Glaucous and Iceland gulls were rare but regular winter visitors. California gulls were unheard of. We got a few great black-backed and almost never a lesser black-backed. I have written before about the suspicion that the recent sightings of California gulls--there was one at the Belmont and Montrose harbors just over a week ago--are more a product of better field guides, better birders, and better binoculars than of any change in the bird's range. However, the black-backed gulls are distinctive, and we know that they are extending their ranges into North America.
What is new is the numbers of these species on the move in January. In the past their major movements began later. Again a phenomenon of February or March is now taking place in what is normally the dead of winter.
Meanwhile there is that saw-whet owl at the Morton Arboretum. The saw-whet is a bird of the northern forests, though there is some evidence of small numbers nesting as far south as Illinois. These birds are--there is no other word for it--cute. About eight inches long, built like a miniature beer barrel with big yellow eyes, they immediately charm most people who see them. A deer mouse might not find them so adorable.
They are known as extremely tame birds. Perching motionless on a branch, they will allow observers to get really close. Of course, holding still is also a fairly effective strategy for avoiding observation, especially if you are only eight inches tall and your perch is the limb of a spruce tree.
Saw-whets arrive around the end of October and leave around the end of March. Or at least they have until now. But what if the overwhelming consensus of scientists who are not on the payrolls of oil companies turns out to be true? What if the mild winters we are experiencing now are not a temporary oscillation like the very cold weather of the late 70s but a long-term shift in global climate?
The short answer is that we don't have a clue. The complexity of ecosystems is such that almost anything might happen. However, we can begin to ask questions based on our experience of ecological change. One question might be, will we still see saw-whet owls in the winter? They are partial migrants now. That is, some birds come south, others stay in the north. Winter food shortages are the likely force behind these movements. If there is less snow cover in upper Michigan, will there be more mice exposed to owl predation? If more mice are exposed, will the forests support more owls? Or will there be any saw-whet owls at all?
Screech owls currently live as far north as the tip of the lower peninsula of Michigan and the southern two-thirds of Wisconsin. They are absent from far northern Wisconsin, the Upper Peninsula, northern Minnesota, and the whole vast realm north of Lake Superior. If the weather warms up, they could extend their range northward. They too are small owls, mouse eaters like the saw-whets. The two species might compete for food. And they might compete for nesting sites; both build their nests in cavities in trees. That sort of relationship is likely to be unstable, and the advantage could lie with the screech owl--especially if climate change is altering the habitat and making it more like what the screech owl is used to.
The presence of large flocks of ducks in southern Lake Michigan in the dead of winter might have a significant effect on populations of local fish, crustaceans, and other aquatic creatures. Thousands of mergansers diving day after day can consume a whole lot. Fish that used to be protected by the ice are now exposed. Could this wipe out some species? Alter the populations of various species enough to lead to the eventual extinction of some? Maybe it will do away with the gobies.
The mobility of birds makes them wonderful environmental monitors, but it may be difficult to determine just what it is they are telling us. The gulls and diving ducks of Lake Michigan seem to be responding to changes in their environment. The ultimate effects of these responses will not be known for centuries, and even then they will be difficult to separate from hundreds of other phenomena happening at the same time. The Romans and Etruscans used to predict the future by observing the flights of birds. Maybe we need a good soothsayer.
In the meantime I worry about what will happen to the lake if the climate around here gets significantly hotter and drier. The lake is deep, but the connecting channels between the lakes are shallow. A drop of just a few tens of feet would isolate Lake Michigan. Everything that flowed into it would stay there. Minerals, especially salt, would accumulate. This is what happened with the Great Salt Lake in Utah. Now almost nothing can live there but California gulls. How's that for a future for our metropolis? Chicago will be the Salt Lake City of the 22nd century.