The Journal from the Heartland has opened up our page to our known writers to present short pieces of work that in one way or another relates to the present lock down, and shall we say isolation and solitude. They have been asked to wonder/wander about making whatever observation they might stumble on.
An observation the other morning as I looked out my breakfast window, amid continuing radio reports of the ravages and turmoil of the Covid-19 pandemic, eased my anxiety and steadied the ground on which I stand. There, on the top of the leatherwood bush beside the feeder, in brilliant sunlight, was an orchard oriole in all his splendor. The virus, in spite of the unimaginable power and technology captured in human society, has emasculated the global economy, and caused us to cower in our homes. Out our windows, however, nature appears unperturbed, a needed reminder that the global ecosystem operates with a wisdom beyond our understanding, but provides the steady assurance that life-sustaining rhythms continue.
While I am cautious about simply going to the local grocery store, the orchard oriole had arrived back in central Wisconsin, having spent nine months in his tropical home, somewhere between southern Mexico and northern Columbia, or northwest Venezuela. There, in the humid tropics, he dined on fruit, nectar, and pollen, sometimes supplemented with insects and seeds. But how did he know when to begin his trip back to Wisconsin, where he will attempt to attract a mate and raise a family in a few brief weeks during the peak of summer.
Clearly, it is important that he arrive here at about the same time as others of his species who will be competing for mates and breeding habitat. But he doesn’t want to be so early that cold weather, even late snow, prevents access to insects and flowers of maple and other early blooming trees on which he will feed until early fruits become available.
For many species, including us, that live in temperate or polar regions, lengthening days stimulate their pituitary gland that, in turn, alters endocrine responses, including sexual activity. Anticipating spring, however, also probably involves warming temperatures, melting snow, and availability of food for species, such as birds, that do not rely on the grocery store.
Meanwhile, in the tropics, the orchard oriole is dining on orchid pollen, or an apricot, or maybe a hibiscus flower, only subtly affected, if at all, by the very subtle change in day length or temperature. Moreover, why should he commit to the rigor and hazards of a thousand mile migration to a less predictable, even inhospitable climate? Orioles, as well as many other true migrants, originated in the tropics and evolved migratory behavior. Why? The decisions about when to go, why to do it, and how to find their way are three profound questions underlying bird migration that have puzzled scientists for decades. As with so much among the wonders of nature, the short answer is no one knows. Indeed, it is the mysterious in nature that provides the wonder and solace for our troubled minds
Research on these questions has not been completely fruitless, however. Many species that live year-round in the higher latitudes are clearly triggered in their movements and reproductive behavior by photoperiod, temperature, and food availability. For true migrants, such as the orchard oriole, evidence suggests that they are less affected by photoperiod, as one might expect, and, of course, we can rule out warming temperature as a trigger. They appear to have an internal clock, an incipient rhythm, that informs them. German scientists have given the increasing restlessness preceding migration a name, zugunruhe. This restlessness is contagious, triggering parallel behavior in other birds, at least of the same species. It is also possible that some true migrants may be triggered by star-gazing. I’ll come back to this, but first let’s consider why they migrate.
The changing seasons at higher latitudes result in two things that are related to the reasons tropical species might migrate. We need not remind ourselves that winters can be brutal in the north. Living things in nature have to shut down tighter than a shopping mall during a pandemic. Food becomes scarce. As a result, many animals move south, and none can sustain a population level greater than that limited by winter’s extremes. However, come spring, growing conditions permit an abundance of food, with flowering, fruiting, and insect populations rebounding all within a few weeks. The surplus of resources, vastly exceeding what the overwintering survivors can use, has, over eons, attracted tropical species to take advantage of the surplus. In their tropical homes, competition, and perhaps predation and disease, has limited their reproduction, but for a few weeks in the north, if they can find their way and time it right, they can bask in the surfeit, and feed their young.
Perhaps even more of a mystery is how true migrants find their way. Even young of some species, hatched in a northern habitat, can find their way alone to over-wintering habitat in the subtropics or tropics. Many of those young, if they survive the migration and over-winter successfully, can find their way back to their natal habitat the following year. That’s where star-gazing fits in. Some true migrants have been proven to orient themselves by stars. Perhaps that’s why many migrate at night, when there is also less heat and less predation risk. Birds also orient with the sun, and with magnetic fields. Less surprising, they also follow geographic features such as coastlines, major rivers, or mountain ranges. Many true migrants can travel a thousand miles or more, some many thousands of miles, and find their way to the same back yard, or even the same tree where they nested six or nine months previously!
Seeing that orchard oriole, who probably had just arrived from Guatemala or Panama, was a wonderful reminder that the natural forces that shaped this wonderful planet are still alive and fully functioning. Our fragile, inept economy is nothing compared to the magnificence of nature. Stay safe, orchard oriole.