Chapter 3: The Odyssean Voyage

Why Robbie decided to stay and live with friendly humans is a case of conjecture. He has always been free to leave, as most birds do, but he chose to adopt this family and the comforts of good food and human servants. In any case, he has never had to fly, like other robins, to winter in Brazil.

The spring migration of robins can be a mammoth trip. Indeed, birds who have wintered in the southernmost parts of the United States may fly to Canadian regions thirty-five hundred miles away in order to breed. Thus, while not quite of Brazilian origins as Melvin mistakenly supposed, the northward trek of redbreasts is Odyssean nevertheless.

Robins are not, of course, the only creatures who undertake these long annual trips. Countless other birds as well as numerous fish (eels, salmon), mammals (bats, lemmings), and even insects (such as Monarch butterflies) boast comparable travels. Although the mysteries of migration have not been completely unraveled for any of these animals, diligent research has managed to answer a few questions—or at least supply a few guesses—about migratory mechanisms. In many avian species, for example, the daily lengthening of daylight that occurs as spring approaches seems to act as an alarm clock that awakens the birds from southern siestas and instills a northbound urge. Changing daylight does not appear to be so important for robins, however, as they are instead governed primarily by trends of temperature. Thus robins, who typically appear at northern regions as soon as local temperatures hit 34°F to 36°F, move up the continent step in step with the latitudinal progression of springtime thaw.

Regardless of whether the complex machinery of robin migration is understood well or poorly, the event is nonetheless filled with inevitable drama for it marks the first step in the great annual renewal of the species. As they journey over hazard and hardship to northern breeding grounds, robins are not merely retracing the fallen footsteps of the previous autumn. They are keeping an appointment with destiny—an appointment they dare not break.

General Migratory Characteristics

We might start off by noting some simple facts about robin migration, such as air speed, the time of day chosen for flying, typical flocking patterns, and the basic flyways that are followed. Robins maintain a fairly steady if unspectacular rate of 20 to 30 mph, flapping their wings about three or four times per second in the meanwhile. Neither statistic deserves much awe since other birds can fly and flap faster (for example, 50 mph for both hummingbirds and eagles, and five flaps per second for goldfinches).

Though plebeian in speed, robins are more elite in their choice of flight time. Most birds prefer to migrate at night, for then they can feed and rest in concealed areas during daytime leisure. Nocturnal navigation, moreover, nicely circumvents predatory threats posed by the diurnal hawks and eagles. Yet robins—who migrate primarily during the day—not only find food quickly enough to afford brief refueling stops along the way, but also seem to boldly ignore the great birds of prey as well. Daytime migration, incidentally, is not without its advantages. For one, robins are not usually among the thousands of migrant casualties who crash into the innumerable television towers that rear up in nocturnal darkness across the land.

Although migrating robins occasionally compress into globular corks that bob along with every ripple of wind, the birds more typically form loose aggregates of individuals who are rather evenly spaced as if uniformly wary of grave underarm offense. In such spacious array, their unending numbers sometimes stretch for scores of miles, especially at the beginnings of their northward trip. One such flock many years ago took fully three February days to pass one spot in Florida. Said an observer of the sight:

They came from a southerly direction, and were continually passing, alighting, and repassing, the general movement being northward. The air was full of them, their numbers beyond estimate, reminding one of bees.

This migrating mass was similarly reported by watchers some ten miles away, across the flight. Thus, ten miles wide and three days long was this ribbony river of robins.

Though there are numerous flyways that robins follow during the course of their trip, a popular one is the Mississippi River Valley. Draining the Gulf Coast and rippling up the great twenty-four-hundred-mile channel, streams of robins eventually branch westward across plains and Rockies by following the Missouri River, and eastward to New England along the Ohio River. In numbers that may top a billion when they first leave the South, their ranks steadily thin because “all along the way, a robin drops off on State Street here, or Elm Street there, as a homing male spots his own backyard” (George, 1964).

Robins do not always follow rivers, however, and in fact they sometimes choose courses that are perpendicular to even the largest of nearby waterways. Often the migrants fly parallel to the north-south ridges of mountain systems, and in general they prefer relatively forested routes to naked stretches of, for instance, prairies. Robins almost never try to cross large bodies of water (lakes, bays, and certainly the oceans) but instead endure lengthy detours in order to stay above dry land.

Other major aspects of the Robin’s springtime migration include the slow progress of the trip (independent of flight speed considerations), its discontinuous nature, and the wavelike effects it engenders. The first characteristic may evoke some surprise since we probably tend to equate the robin’s renowned early arrival with a quick trip. Quite conversely is true, however, as it is earliness and slowness that go hand in hand in avian migration. Since robins advance up the continent on the somewhat sluggish heels of spring, they cannot fly too fast without overtaking the warm front and crashing head-on with northern storms. In contrast, other birds who remain South until springtime temperatures have already arrived in the North, can migrate much faster and still encounter only mild weather throughout their trip. As an example, suppose that spring takes fifteen days to cross the New England states; migrating robins may cover the same territory in sixteen or seventeen days, while other species coming at a later date may need only a week.

Besides being slow, robin migration is riddled with discontinuity across individual birds as well as across geographic regions. Epitomizing individual variability is the often reported observation that some robins temporarily fly in east-west directions or even south, despite an overall northward progression by the general population. A given bird, furthermore, may travel 200 miles in a single fight, only to spend the next day or two foraging in one area while fellow migrants pass by. Because of these great individual differences, the migration of the robin population as a whole—which of course represents the average of many individuals—always displays a much steadier pace than that characterizing its component members.

Several examples can be cited to represent regional variability in migratory progression. For one, robins near the Pacific coast usually tend to migrate faster than those in either the middle or the eastern parts of the continent. For another, robins typically travel faster as they get farther and farther north, almost as if they were increasingly anxious to get home. Thus birds who flew a mere fifteen to thirty miles per day at the southern start of their trip may average more than a hundred as they enter Canada and head northwesterly for Alaska.

Still another element of migratory variability involves local weather conditions. Instead of simply plodding north until their breeding grounds are reached, robins accelerate during unusually warm periods and, conversely, reverse their progress whenever temperatures drop too cold for their liking. Many a birdwatcher has been astonished to observe robins approaching from the north rather than from the south during a March cold spell. Such influxes can be surprisingly abrupt as the wide-ranging redbreasts employ their tremendous avian mobility to shadow the often-elusive springtime warmth.

In sum, robin migration is a phenomenon that is extremely discontinuous in nature. The trip is thus not analogous to the steady creeping of the morning sun, whose rays uniformly dawn from east to west. Rather, it is akin to the rising tide which, though consisting of individual advances and recessions, gradually climbs higher and higher up the beach as each wave tends to progress a bit beyond its predecessor.

And speaking of waves, we now come to a final general characteristic of robin migration—namely, the wavelike effect that occurs as the population rolls through a given locality. Should, for example, citizens of Cincinnati, Ohio begin watching for robins in February, they might initially see only a sprinkling of redbreasts, these representing the eager-beavers of the species. Somewhat later would come the “crest” of the wave as hundreds and thousands of birds—constituting the bulk of the migration—spill into the city over the span of a few days. As most of the migrants move on, the wave would finally spend itself until only a few splatterings of robins remain. These latter individuals would be the city’s summer residents, those birds who will breed within the unnatural urban environment along with countless other Cincinnatians.

Similar waves of robins can be observed by simply driving one’s car southward during early March. One man who did this saw no robins as he left Minnesota, but then

recorded an occasional robin in northern Iowa, great numbers through central and southern Iowa, and a steady decrease in numbers through northern Missouri, until in central Missouri there were only scattered individuals, presumably the birds that were to become summer residents there.

This wave, slowly rumbling up the North American landscape, was estimated to be some two hundred twenty-five miles in breadth—a veritable surfer’s dream.

Sure Signs of Spring?

Each March, northern newspapers eagerly report the first sightings of robins in nearby locales. Old Man Winter, after all, can be a depressing sort of fellow and most people are happy to read about his demise. How many of us, upon spying our first robin of the season, have experienced an emotional uplifting similar to that conveyed in the following passage:

When they come back, what good cheer they bring with them! I remember one long winter spent in the country when it seemed that spring would never come. At last one day the call of a Robin rang out, and on one of the few bare spots made by the melting snow there stood the first redbreast! It was a sight I can never forget, for the intense delight of such moments makes bright spots in a lifetime.

But do robins really serve as accurate gauges of spring’s arrival? Partly no, and partly yes. Partly no because not all robins migrate south for the winter; some remain in the North. Thus it is perfectly possible to see a nonmigrating holdover as your “first robin” when Mr. Winter is still in his prime. And partly yes because the large majority of robins do in fact fly south for the winter and then promptly reappear in the North with the return of warm weather. These latter birds, then, are reasonably legitimate springtime harbingers.

How, as March approaches, can you tell whether that robin on your lawn is a genuine migrant or merely a mimicking imposter? Two clues will guide you: First, robins who have arrived from the South will for at least a short time remain in flocks of a dozen or more individuals. In contrast, the winter holdovers—who have had to contend with thinly scattered food supplies—are usually alone or in pairs at most (more may temporarily gather at, say, a birdbath). Secondly, the migrants will still be fat and fit from southern feasts, while the holdovers are haggard and scrawny from fighting freeze and famine in the North. Still, by mid-February, even a scrawny robin is a welcome sight and we are not apt to quibble over such technicalities as we hasten to bid winter adieu.

Another often-asked question concerning the first robins of spring is whether the initial arrivals are simply transients en route to breeding grounds farther north or are instead the birds who will comprise the area’s resident redbreasts during the upcoming summer. While many observers claim that local robins appear at a given locality before more northbound migrants, just the opposite has occasionally been reported as well. There may in fact be little reliable difference in the respective arrival times. The two sets of birds, however, can often be readily distinguished because the local residents soon separate into individual territories and begin singing with vigor, while the transients typically remain mute and in their migratory flocks.

The American Robin is, in any event, a habitually early migrant. One enterprising ornithologist kept track of springtime arrivals in southern Connecticut over a forty-year period; the average arrival date for robins was March 10—fourth earliest of fifty different species, with grackles, redwing blackbirds, and bluebirds only a day or two earlier. Robins apparently lack the incredibly accurate wristwatches of Capistrano’s swallows, as the exact date of redbreast arrival varies with the weather from year to year. Yet across decades a remarkable stability can emerge. At Williamstown, Massachusetts, the average date of spring’s first robin from 1816 to 1838 was March 15; a century later, during the years 1916 to 1938, the average was again March 15.

Springtime Storms

One unfortunate by-product of early migration is the threat presented by sudden snowstorms which, trailing warm spells, may strike after robins have already arrived at their breeding grounds. Should these storms consist of icy winds and heavy snows that batter the birds for several days in succession, the elements may prove fatally harsh. Indeed, numerous cases are on record where March blizzards in northern locales have killed robins by the hundreds and thousands.

Even mild snowfalls can blanket local food supplies and create problems for early migrants who, now on their own territories, are loathe to return South. Under these conditions, robins become opportunists and quickly exploit any windfall of foodstuff that happens their way. Thus redbreasts will flock to birdfeeders filled with mealworms, and the tiniest patches of bare grass are hunted over and over again by every robin in town. Once after an April snowstorm in New Hampshire, robins even flocked around farmland manure heaps to prey upon the hordes of flying insects that had gathered there in dungful delight.

Naturally, robins are not entirely altruistic when feeding at close quarters upon limited food supplies. Once after a kindhearted birdwatcher overturned a clump of worm-writhing earth in an otherwise snowy field, a male robin greedily claimed the mound as his own. When not chasing other birds away from his treasure chest, the rapacious redbreast ate so much that finally he couldn’t even close his beak. When last seen, the selfish squatter was crouched atop the wiggling stockpile with a worm dangling from his bill, still refusing to surrender his claim.

Whether springtime snows are lethal or merely hardships, they raise the question of why robins go north so early in the first place. Why don’t they simply remain in the South, with its warm temperatures and adequate food supplies, until the last remnants of winter have vanished from northern breeding grounds? The timing of spring migration actually represents a delicate balance between the advantages and disadvantages of an early trip. The sooner the birds get back north, the sooner they can establish territories, select mates and breed; thus they can more easily raise two or even three broods during the upcoming season, with obvious benefits for the species. But this advantage must be weighed against the threat of late blizzards that can kill early migrants; indeed, even if the adults survive, the eggs and young of the season’s first brood may be destroyed by springtime chills.

Of course robins themselves do not ponder these matters when they test the air for signs of spring. Their behavior is simply the product of natural selection. Those birds with propensities for premature migration are weeded out of the population by the harsh wisdom of northern storms. Those who have a tendency to migrate too late will, upon their arrival in the North, find all of the attractive territories already occupied and so will have difficulty obtaining mates and breeding. Thus, while late migrants will not die like premature migrants might, they will nonetheless be unable to pass on their tardy tendencies to other generations of redbreasts.

Territorial Return

One of the most remarkable aspects of robin migration is the return of individual birds to their previous breeding grounds. Eastern-bred birds, for example, would almost never migrate to the West in the spring, even though other robins they wintered with may head off in a westerly direction. In one study, researchers found that about 55 percent of robins returned to the exact community where they had been hatched the year before; another 20 percent returned to within ten miles of their birthplace, and less than 10 percent settled one hundred or more miles away. Interestingly, all of the robins who settled relatively far from their birthplaces chose more southern spots as their new homes (that is, they did not settle east, west, or north of their birthplaces). Perhaps during their return from the South these individuals were prematurely lured out of the migrating flock by some especially appealing terrain.

Given the immensity of the robin’s potential breeding grounds (from coast to coast across Canada and the United States), these return figures are nothing less than incredible. How does a robin find its way back to your backyard after spending the winter a thousand or more miles away? We can only speculate. Such gross navigational aids as the stars, sun, mountains, and rivers may guide birds back to the state or province of their birth, and this is remarkable enough a feat in itself. But how can a year-old robin pick one backyard out of thousands when I can get lost going to a new supermarket on the other side of town?

At least one thing seems clear. Robins—more particularly, the first-year birds—do not really return to their actual birthplaces so much as to the localities from which they disembarked for their first southern migration. Normally, these two places (birthplace vs. point of migratory departure) are virtually identical since young birds do not wander any great distance from their nestsites before migrating in the fall. In one experiment, however, a robin who had just left its nest was captured in Long Island, New York, and was then released seventy-five miles westward in Passaic, New Jersey. For the next three years, this bird returned to Passaic—not Long Island—after wintering in the South.

Not all Robins, by the way, are equally precise in reoccupying their old haunts, for there seem to be both sexual and age differences involved. In general, males are more likely than females to resettle the same territory as was held the previous season, and similarly, adults are more likely than first-year birds to return to the same spot as before. This is not to say that females are unknown to nest in the exact location—a certain tree, a particular porch—year after year after year; indeed, numerous such cases have been reported. But overall, both females and youngsters tend to return to the same general region of the previous season, but then settle wherever they find a suitable mate and/or territory.

Related to these differences in territorial return is the tendency toward both sexual and age separation during migration itself, for males in general precede the females, and adults in general precede first-year birds. For various reasons, these separations occur predominantly in the lower half of the continent (45°N latitude and below) and almost disappear by the time the Canadian provinces are reached. Interestingly, the birds’ reproductive glands—whose enlargement coincides with the start of spring migration—happen to expand in males before females, and in mature birds before those who hatched the year before.

In explaining the preceding of females by males, one turn-of-the-century ornithologist simply noted that the males migrate “in advance of their less hardy mates … to be followed by the females a week or so later when the weather is less severe” (Howe, 1898). Presumably that writer would have suggested a similar explanation for the migratory lagging shown by the “less hardy” robin youngsters. In a less chauvinistic vein, however, the time-priority of males and grown-ups before females and adolescents ensures two beneficial effects: First, the early arriving males have time to secure their previous territories without having to simultaneously worry about wooing females (if territories and females were in flux concurrently, the poor males might wear themselves to a feathered frazzle). Secondly, the adults, who are of time-proven fitness, have first choice of northern nesting territories; in contrast, the less experienced first-year birds must contest among themselves for territories vacated by owners now deceased.

One final point about the robin’s faithful territorial return involves the functional isolation of breeding populations. Since robins do not randomly resettle after migration but instead return to specific localities year after year, interbreeding across localities is relatively rare. Mountain systems in particular can reinforce this isolation effect; in one study, researchers failed to find a single instance of a robin who had hatched on one side of the Appalachian Mountains breeding on the opposite side during successive seasons. Such lack of interbreeding among groups no doubt contributed to evolution of the different races of redbreast that now reside in various corners of the continent. Whether these races will continue to diverge until wholly distinct species are created is, of course, a matter of conjecture.