Chapter 10: Roostville, North America: A Robin Metropolis

At sunset the sky is black with robins coming in to roost, and at daybreak when they are leaving the sound is like a train passing over a long trestle.

Many of us, probably, hide something about ourselves—something secret, something very private, something perhaps even dark. And no matter how openly we may relate to other people, we may always have within us one or two personal facts that would startle even our close friends were they to discover them. It should come as no surprise, then, that the American Robin—that trusting, sincere, straightforward-appearing bird—should keep secrets as well, habits that are little known and even less understood. But for me, nothing about robins remains as baffling or as intriguing as their habit of communal roosting.

By “communal roosting,” I refer to the robin’s practice of flocking in one place to spend the night. Although the mammoth winter roosts that robins form in the South had been known to ornithologists for a long time, the birds’ summer roosts remained unreported until much later—near the turn of the last century, which is remarkably recent considering how well-known a bird the robin is. Even today the fact that robins roost in flocks each night is news to most laymen, while many fundamental questions about the phenomenon have yet to be adequately answered even by scientists.

Who Roost?

As soon as they reach their breeding grounds in spring—even before the females arrive—male robins begin congregating in roosts at night. Already a perplexing mystery is posed: How can a bird who spends all day vigorously defending his territory against redbreasted conspecifics suddenly surrender his pugnacious spirit and actively seek the companionship of his fellows? What magic is this that turns a lustful daytime gladiator into an affable fraternity brother at night? Whatever the potion, its Jekyll and Hyde effects are spectacular. (Note: While some observers have reported that breeding males do leave their territories to join a communal roost, others believe that summer roosts are composed primarily of unterritoried and non- breeding “floaters.” This point remains unsettled.)

Though females too spend evenings at the roost when they first arrive after migration, they do not do so throughout most of the summer. For the most part, while the males hold their nightly stag gatherings, the females are stuck home incubating their eggs and brooding their young. Even when the first brood has finally fledged and become airborne, Pop Robin takes his speckled youngsters to the roost while Mom begins the egg-laying and incubating chores that the season’s second brood necessitates. It is only after this second batch of young is fledged that the females—finally freed from family functions—fly roostward with the males as part of their daily routine.

All of this means that roosts which begin with mere dozens of males in the spring grow dramatically in size as first broods, second broods, and finally females join the robin ranks each evening. By mid-September, hundreds and even thousands of robins flock together as if to celebrate the end of another successful season of species proliferation. These noisy nocturnal gatherings continue until fall migration commences, and then the once-bustling roost becomes empty and abandoned until the following spring.

In addition to increases from the local population, contributions to the roost’s numbers also occur in early autumn when premature migrants—originally from other breeding locations but now passing through the area—follow local residents to their bedchambers. For a specific example, let’s drift back and listen to one of the two pioneer reports on robin roosts:

Some of the robins appeared to be ignorant of the precise whereabouts of the roost. …I took special note of one fellow who came from the South at a great altitude and went directly over the wood. When he was well past it he suddenly pulled himself up, as if fancying he had caught a signal. After a moment of hesitation he proceeded on his northerly course, but had not gone far before he met half a dozen birds flying south. Perhaps he asked them the way. At all events, he wheeled about and joined them, and in half a minute was safe in port. Apparently, he had heard of the roost (how and where?) but had not before visited it.

Incidentally, at almost precisely the time Bradford Torrey made public his rather startling, if anthropomorphic, observations on summer robin roosts, a similar revelation was being effected by fellow New Englander William Brewster. This apparently constituted a case of that type of simultaneous but independent discovery—reminiscent of the Wallace-Darwin breakthrough concerning evolution—which comprises an interesting sidelight in the history of science.

In addition to their summer roosts, robins, as mentioned earlier, also form roosts during their winter stay in the South. These roosts, drawing on birds who have migrated from all parts of the continent, are sometimes immense beyond accurate description. Robin Roosts covering a hundred acres have held what conservative observers estimated to be upwards of fifty thousand. One forty-acre tract of Alabama swampland, used as a roosting site during the late 1920s, attracted robins in “almost inconceivable numbers,” estimated at a million redbreasts by one perhaps exaggerating observer.

Where Roost?

Almost any area of dense vegetation, with many young saplings and plenty of thick (and preferably berry-laden) shrubbery, will serve as a roosting site. Often the location will be relatively remote from human habitation; frequently it has a field or lawn nearby where pre-bedtime snacks can be gotten, as well as a stream or brook for drinks and baths. Secluded woods within golf courses or cemeteries as well as relatively inaccessible swamps appear to be especially attractive roosting spots.

Under certain circumstances, though, robins will even roost in open fields among grasses and clover less than six inches high. Such roofless roosting seems to involve migrating individuals who were unceremoniously forced down by suddenly bad weather—high winds, rain, snow. Any port in a storm, you know. But these emergency bivouacs are rarities; robins much more typically rest at long-established encampments that are well hidden within luxuriant foliage.

Yet the exact manner by which robins settle upon one particular place to locate their roost is a real mystery. Other sites near a given roost may actually afford better protection or offer more abundant food than the roost itself. And although robins—if unduly persecuted at their roost by man or beast—will move to another location, they sometimes suddenly abandon roosts that have been faithfully used for a decade or more, without any discernible reason whatsoever. No doubt it is the mature and experienced birds who guide the general population to a given roost (as, for example, when fathers lead their young). But how new roosts are initially established and why old ones are eventually abandoned remains a puzzle.

Methods of Approach

Except for juveniles who follow their fathers, robins heading roostward typically travel in loose flocks, reminding one of last-minute Christmas shoppers who, though doing the same thing together, nevertheless do it with a distinct air of mutual independence. The exact manner of approach to the roosting area varies from roost to roost and even from night to night.

Sometimes robins will fly close to the tree-tops, stopping here and there along the way as if the distance were too great for them to traverse at once (which of course it is not). At other times the birds may come in a continuous flight at great heights—so great that their bodies are difficult to see against the dimming sky; then, when finally above the roost, they fold in their wings and drop into the foliage like a hailstorm of wounded ducks. At still other times, robins skim along the ground as they approach the roost, weaving to and fro among tree-trunks and bushes. What determines these different fight patterns is unclear, although important factors probably include weather (flight altitude may be lowered during rough, windy weather) and the total distance from nest-to-roost (robins traveling five miles to the roost each night may fly sky-high while those coming from a mile or less may hopscotch along the tree-tops).

At a cemetery roost I visited in Pennsylvania, scattered groups of robins appeared to approach the general vicinity of the roost by flying at tree-top heights with periodic rest-stops. Most arrived with a good hour of daylight remaining, and during that time they fed in typical robin fashion on the lawns of nearby homes as well as on the neatly groomed grass of the cemetery itself. As they foraged they gradually hopped their way toward the roost, which sat at the bottom of a long sloping hill gravely landmarked with tombstones. By the time the light was quite dim, most robins were within three hundred yards of the roost, and the flock covered this final stretch of ground by nearly simultaneous flight.

Like leaves hurled by a strong autumn wind, dozen upon dozen of auburn robins skimmed over the ground just above the tips of vertical gravemarkers. More than once as I sat perfectly still on the cemetery lawn, I felt sure my head would abruptly meet the beak of some careless individual who—caught up in the excitement of the flight—might fail to swerve aside in time. But fortunately, my head (which cannot afford any leaks) remained unpunctured by the skillful flyers.

Robins, incidentally, do not always roost by themselves but instead are often joined by one or more other species of bird. Grackles, cowbirds, swallows, buntings, thrashers, blackbirds, cedarbirds and orioles are just a few of the congenial species who sometimes share sleeping accommodations with robins. Usually the different species intermingle among the branches, but at one roost I noticed that numerous crows slept in strict segregation a hundred or so yards from the robins. Multi-species roosts are interesting to visit because they usually provide contrasting examples of roost-arrival, with some species (for example, starlings) flying in tight flock formation while others (like our robin) approach in small loose groups or even singly.

Robins in Captivity

It’s been known for a long, long time that when a migratory species of songbird is kept in captivity, it shows increased activity during the times of year that the species would normally migrate. This seasonal increase in activity (which captive robins, incidentally, show) is called migratory restlessness and reflects the urge to migrate. As discovered by your author, a comparable phenomenon is shown by robins living in captivity except that the increase in activity occurs every day at dusk. This daily increase in activity is called roosttime restlessness and reflects the urge to travel to the communal roost site.

Roosttime restlessness first appears in young captive robins at just about the age when wild fledglings would be making their first trips to the roost site. The restlessness at dusk occurs during every month of the year (unlike seasonal migratory restlessness), and it’s suppressed in captive incubating females just as it is in wild females who must remain on their nests rather than traveling to a communal roost site. Finally, roosttime restlessness occurs in captivity among robins and other species who use communal roost sites but it does not occur in species that do not roost communally.

Similarities Between Communal Roosting and Migration

Similarities between communal roosting and migration, as reflected in the American Robin, are intriguing to contemplate. Both phenomena involve significant distances to be traveled, up to 5-10 miles in the case of roosting and hundreds of miles in the case of migration. As noted above, both are reflected in behavioral restlessness when robins are maintained in captivity. And both represent fundamental rhythms in the robin’s life cycle, roosting being a daily rhythm and migration an annual rhythm.

Finally, both roosting and migration are correlated with a fundamental shift in the robin’s “personality.” Although

robins are territorial and thus basically antagonistic towards other robins during the daytime in the breeding season, the birds become sociable flockers during both communal roosting and migration. Also, while breeding robins are bold creatures during the daytime—birds who often can be closely approached and who often nest in areas of high human activity—they become more skittish and wary at the approach of humans both at their roost site and during the migration season.

These similarities suggest common physiological substrates (shared brain chemistry and anatomical structures) mediating both roosting and migration in robins.

Survival Value

Why, we may now ask, do robins roost together instead of simply spending the night at individual resting spots? It’s difficult to say. Despite the fact that robins usually select heavily vegetated areas for their roosts, they nonetheless are no safer there than they would be at their nest sites. In fact, just the opposite may be true. Scattered out in their respective territories, robins could never suffer concentrated predation at night; gathered together in densely populated roosts, they become much more vulnerable—even a single predator can wreak considerable havoc among them. Indeed, bobcats and other nocturnal predators are especially attracted to these roosting areas where they can feast among startled and disoriented sleepers.

Thermoregulation is another potential benefit of communal roosting. Robins might be able to reduce energy demands by sharing body heat and reducing the impact of wind while roosting together. Of course this would not apply to the communal roosts that robins form during the summer.

A benefit of roosting during the summer might be the preparation it affords young robins for the mammoth undertaking of fall migration. Not only can the daily flights help strengthen the developing wing muscles of young birds, but through these mini-trips youngsters can also develop the habit of following their parents and at the same time gain experience in navigating over at least short distances. A good way to prepare for a long trip, after all, is to make numerous shorter ones. These factors, then, may prove important preliminaries to the impending migratory voyage.

Roosting Sensations

Strange sounds and sights await an observer at a robin roost. First, there is the flapping of winged multitudes as they enter the roost, each bird silhouetted for a fleeting instant against the dimly lit sky. The predawn exodus the next morning is even more impressive since the birds leave the roost more simultaneously than they entered it. At some of the larger winter roosts in the South, where thousands of robins are in the air at the same time, the resulting stimulation can awe one’s perception (as suggested by the quote at the beginning of this chapter). At a three-hundred acre South Carolinian roost whose population was estimated at fifty thousand robins, one local resident went so far as to claim that when birds flew in, his head could feel wind generated by their wings. This man apparently was either short on hair or tall on tales.

Then there is the flutter of wings within the leafy roost as newly arrived birds attempt to secure an unoccupied twig among overpopulated branches. Usually this constant rustle combines with general bird-talk which, because of the innumerable conversationists involved, amounts to a rocky surf roar. Indeed a lone observer standing among thousands of fluttering and squabbling robins in the dense vegetation of a darkened roost might, with just a little imagination, experience the same sort of subtle fear that overtakes one amid screeching parrots and wailing monkeys in the Amazon’s deepest jungle.

Even after night passes and all the birds have departed for their respective territories, a robin roost is still worth a sightseeing trip or two. Now quiet and deserted, it is a place to linger and reflect upon the booming population it hosted only hours before, and which it will once again hold a few hours hence. Like an historic Nevada silver-mining town, the daytime robin roost seems a rather ghostly site. Were teeming hordes really there so short a while ago? Indeed, in the blunt reality of the shining sun you might even deny the events of the preceding night were it not for the robin snow all around you.

Henry David Thoreau used the term “robin snow” to refer to a springtime storm that fell after robins had arrived from the South, but for me the term has quite another meaning: The white droppings of thousands of robins which accumulate night after night on the ground beneath the birds’ perches like just so much winter precipitation. This snow will be the only daytime testimony bearing indisputable witness of the nightly visitations of Turdus migratorius to the silent, empty woods where you now stand.

There are, then, many mysteries surrounding the robin’s secretive habit of roosting. Questions abound concerning the birds’ sudden congeniality, the nature of their approach flight, their choosing of particular sites and their abandonment of others, and the exact biological adaptiveness of the roosting habit itself—all these questions are still answered by scientific speculation rather than documented fact. But to at least get a perspective on how roosting fits into the robin’s daily routine in at least some cases and according to some ornithologists, we might summarize a robin’s activities on a typical midsummer day.

Upon awakening an hour or so before dawn when the sky still sparkles with stars, Pop Robin leaves the roost and returns to his mate who has slumbered on her nest. He then spends the day singing, defending territory, and helping to feed and protect any nestlings or fledglings that the mated couple may have. As twilight approaches, our avian commuter sings a final tune from his favorite perch, bids goodnight to his “lady,” and takes off for Roostville, perhaps with other males from his neighborhood and certainly with his juvenile young tagging dependently behind.