Chapter 8: Banquets of Bugs and Berries

As I released the football player from the folds of my mist net, I explained that I was collecting robins, and that robins landed on the football field during his scrimmage hours. He made a rude and profane remark. I shrugged, picked up my paraphernalia, then trundled back to a little patch of ground behind the handball courts at San Francisco State College, where I was to spend the next year and a half trying to discover how robins find worms.

Robins hunting on a lawn. The sight, so familiar to us all, bespeaks of things unchanging, even eternal, in Nature. The robin on your grass is not simply a bird looking for food; he is an institution. And he knows it. Look how proudly he carries himself! See the way he flaunts his craft, first standing stone-still erect, then scurrying abruptly, now stopping again. He cocks his head and you know he’s found his mark; an instant later, a wiggling worm knows it too.

And worms are not particularly easy to catch. They’re difficult to see among stalks of grass, they’re quick to retreat into burrows if one’s first grab is the merest bit off target, and even when squarely nipped they are tenacious clingers to their tunnels. Yet robins, more than any other bird on the continent, excel at nabbing these miniserpents. They even make it look easy.

Do I exaggerate the robin’s skill? I once saw a starling furtively following a robin across a lawn; whenever the robin succeeded in pulling up a worm, the starling made a hopping charge and snatched the snack abandoned by the retreating redbreast. After swallowing the loot, the black bandit again trailed the robin and repeated the crime. Many other unscrupulous species have been known to similarly exploit the robin’s unparalleled lawn skills, including English Sparrows, Brown Thrashers, and even Sea Gulls. These birds are not thieves because they are lazy; they steal because they are inept. At least when compared to our robin. Truly, catching worms is not so easy as the redbreasted pro always makes it appear.

We will return to the worm-hunting habits of robins later, but first let’s embark upon a more general survey of their diet. For even a robin would agree that life is not just a bowlful of annelids.

Natural Diet

The natural food of robins consists wild fruits and small animals. The relative proportions that these two categories contribute to the bird’s overall diet changes with both time and place. In fall, when insects become scarce and fruits ripen, vegetal matter may be the robin’s only food; during early summer, the opposite may be largely true. Diet also varies with habitat since robins living deep in forests will not find as many earthworms as do those who picnic in your backyard. Finally, local concentrations of specific foods may temporarily capture the birds’ entire gastronomic attention, as happens during the massive and periodic emergence of seventeen-year locusts. On the whole, however, the robin’s menu consists of approximately 40 percent animal matter and 60 percent vegetal matter.

The animals upon which robins prey include more than just worms. Fair game are caterpillars, beetles, weevils, grasshoppers, flies, snails, spiders, termites, wasps, and really any larvae the birds can bill. Similarly, hardly a fruit or berry exists that robins don’t like, though they do have their preferences. The varieties are too numerous to list completely but a few are cedar berries, dogwood berries, honeysuckle berries, wild cherries, blueberries, blackberries, sumacs, hollies and mulberries.

Frequently the seeds of these fruits remain viable after passing through a bird’s body, and consequently robins help disseminate the plants they patronize. With cherries and olives whose pits are too large to pass beyond the stomach, robins actually disgorge (force back out through the throat) the stones after the fruit’s flesh has dissolved. Thus after stuffing itself with cherries, an individual may sit quietly somewhere and then, within a half-hour’s time, cough up the stones in a convulsive but satisfying belch. This peculiar process, which results in a pile of clean cherry pits beneath the bird’s perch, is comparable to the way in which an owl handles the skulls and bones of mice after swallowing them whole.

Because of the robin’s fondness for fruit, and because fruit ferments quickly when the weather is warm, robins occasionally suffer the role of dupe in one of those amusing little pranks that Mother Nature plays upon her creatures every now and then. For after imbibing their fill of fermented berries, poor unsuspecting robins show all the signs of inebriation. They flap, flop, flitter and flutter; they trip, traipse, teeter and totter; they slip, slide, stumble and stagger. Sometimes they even pass out. But by the next day they will have recovered sufficient sobriety to fly safely away, birdy hangover and all.

In addition to their basic bug-’n-berry diet, robins are always ready to dine on more exotic foods should the opportunity arise. Mice, snakes and fish are among the surprising meals that epicurean robins have been known to enjoy. Admittedly, the evidence for mouse-munching is scattered and a bit circumstantial: one robin swallowed a mouse headfirst after the rodent had been killed by a dog; another dive-bombed a mouse scurrying across a lawn, killed him in a pecky assault, and then flew away with the corpse; a third redbreast was seen incubating the headless body of a white-footed mouse in her egg-filled nest (only the eggs hatched, I think); and a fourth robin, this one an albino, once fought a mole with mutually fatal results.

Robins have several times been known to kill small snakes, including northern brown snakes, garter snakes and ribbon snakes. With even small serpents, gulping down the reptile is a real problem quite apart from killing it. One male robin staggered around a Florida swamp for twenty minutes with ten inches of half-swallowed snake dangling from his beak before finally fluttering out of sight. Another drawback of trying to eat these overgrown worms is that they have an obstinate inclination to defend themselves. Several robins have been strangled by sneaky snakes who managed to coil around their would-be consumers.

As for fish, those few redbreasts who live by lake or sea may habitually visit the shorelines and pretend they are sandpipers, but most fish-eating robins are only exploiting windfall opportunities. Thus robins have eaten minnows discarded by fishermen about Wisconsin docks, gobbled up trout fry recently “planted” by wardens in California creeks, and feasted in the shallows of Iowa lakes following ammonia-caused fishkills. Occasionally robins actually seek out seafood, especially when their traditional terrestrial meals are temporarily unavailable, as occurs following a ground-covering snowstorm or during a lawn-parching drought.

Before we leave the robin’s natural diet, some mention should be made of an insect that is seldom eaten yet often relished by redbreasts—namely, the ant. Anting, a peculiar behavior performed by many birds, can either involve active insertion of live ants among the feathers, or else passive squatting by which the bird permits ants to crawl within its puffed-out plumage before preening them away. In either case, the accompanying preening movements—which are directed under the wing, along the tail or around the vent—are often so vigorously violent that the bird staggers or even somersaults for want of balanced restraint.

On one interesting occasion, an anting robin repeatedly swept the litter-covered ground with a twig held in its bill in apparent efforts to locate the scurrying insects. Such tool-using behavior is rare in the animal kingdom outside of humans. Wild chimpanzees sometimes poke sticks down termite holes and then, after withdrawing the instrument, lick it clean of clinging insects; sea otters mash mussel shells against flat stones; solitary wasps hammer dirt into burrows with mandible-pinched pebbles; and Egyptian Vultures crack thick-shelled ostrich eggs with well-aimed rocks. For various reasons, scientists do not consider all of these tool-using examples as indicative of unusual intelligence. Even by scientific standards, however, the twig-twirling robin portrayed pretty brainy behavior.

Frequently though not always, anting is temporally associated with other body-oriented activities such as sunning and bathing. The exact utility of anting, however, is still open to question. According to various theories, birds ant in order to: (1) induce sexual or other sensual pleasure; (2) utilize the formic acid or some other substance contained in ants to repel ectoparasites; or (3) soothe, again via ant substances, irritated skin. Since anting occurs most often during August, when the majority of North American birds are molting and hence growing new feathers, the skin-soothing suggestion is favored by many researchers over either the masturbatory or antiparasitic propositions.

Cultivated Crops

The blueberry episode in New Brunswick (Chapter 7) was but one example of robin depredation upon cultivated crops. Besides blueberry fields, robins have most notably feasted off cherry trees, strawberry patches, olive groves and, to a lesser extent, raspberry gardens and grape vineyards. Figs, pears, prunes and apples are also occasionally nibbled, but usually in quantities that are quite insignificant and which in any case involve mostly waste fruit passed over as subpar during the previous harvest.

Of the vegetative portion of the robin’s diet, wild fruit accounts for ten times as much as cultivated fruit; indeed, less that 5 percent of the species’ food in general is human-grown. Many robins never even have the opportunity to take cultivated food since they live deep in forests or in other areas not inhabited by people. Still, it cannot be disputed that in some cases robins do real harm to crops. You cannot, after all, have ten thousand fruit-loving redbreasts sitting in your blueberry field and expect anything less than grand larceny. In the West, where enormous flocks of robins are sometimes attracted to the olives there, the losses are

often serious and occasionally disastrous. In some cases it is necessary to employ men with shotguns and keep them constantly firing, in order to save more than 50 percent of the fruit. Some of the birds have as many as six olives in their crops.

Several points, however, can be made on the robin’s behalf. First, instances of serious robin crop depredation can almost always be traced in origin to regional scarcity of the bird’s natural food supply, and these scarcities are in turn often the direct products of human activity. Such was clearly the case in New Brunswick where blueberry banqueting by redbreasts was precipitated by a pesticide campaign that had obliterated a large part of the bird’s normal foodfare. More generally, humans have destroyed the habitats of many wild fruits—through ax, plow and bulldozer—and this has led to widespread dwindling of that portion of normal robin sustenance. From whence, then, do we derive the audacity to dispense capital punishment for “crimes” that we ourselves have directly instigated?

Secondly, robins are without doubt overwhelmingly beneficial to crops because they devour so many insects. Bugs, not birds, are our chief competitors on this planet, particularly where foodstuff is concerned. And do you remember the astronomical numbers of potential descendants of a single pair of robins? Well, those numbers are infinitesimal next to comparable calculations for any insect you care to mention (a single pair of houseflies, for example, has the potential for 191 million trillion descendants within one year). So each time Mother Robin procures a couple of beetles for her nestlings, she is doing far more than saving the farmer’s crops from just those two tiny mouths; she is obliterating the potential for billions who—if not negated by robins and other bug-eaters—would soon engulf the world itself, much less a farmer’s field.

Consider this example of the Robin’s insect-controlling ability: Once in a wooded area where insect larvae had become numerous, a flock of two hundred fifty robins suddenly appeared and within three weeks had consumed an estimated two hundred thousand of the larvae as well as twenty-one thousand beetles and sixty-six thousand members of a large insect order called Hemiptera. Together, these dispatched bugs accounted for about 80 percent of the entire invertebrate population living within the local forest litter. Similarly impressive insect ingestion has sometimes been spectacularly instrumental in crop salvation: Robins have been credited with saving southern cotton crops from weevil wreckage, Massachusetts cranberry bogs from white grub demolition, Texan grain from armyworm annihilation, and Ohio hayfields from Marchfly mastication.

Even in the absence of such heroics, however, robins are always quietly but effectively going about their insect-checking work to the most direct benefit of the farmer. Yet despite this good reason for accepting robins as allies, some folks persist in viewing them as foes. Thus the following words, now so old, could still apply today:

I have known instances where a robin who had saved from ten to fifteen bushels of apples that were worth a dollar per bushel, by clearing the trees from cankerworms in the Spring, was shot when he simply pecked one of the apples that he had saved for the ungrateful fruit-grower.

Under conditions of moderation, then, it would seem that robins rightfully deserve at least some portion of the crops they save, as justly earned retribution. But how can moderation be preserved? Of the several methods available—all of which are fairly effective—perhaps the easiest and most commonly used has been the shotgun approach. Despite its popularity, however, this method is thricely flawed since it destroys a largely beneficial bird, defiles the reverence that all Nature warrants, and demeans the human spirit. Better alternatives exist.

In the case of blueberries, nets can shield the fruit from birds; while obviously not in use in New Brunswick, such nets are effectively employed as a matter of course by many blueberry growers in the United States. In similar fashion, cherry trees can be screened from avian snacking. Considerable expense, it is true, is involved with such nets and screens but governmental subsidy can reasonably be expected for such purposes. Preservation of wildlife, after all, is not a responsibility that should be borne alone by farmers or any other single segment of society, but by us all.

A really nice solution to the problem involves the strategic planting of attractive wild fruit near cultivated crops. Mulberry bushes are excellent for this purpose as they are vigorous in growth, bountiful in berries, timely in ripening and absolutely adored by robins. Thus if a few mulberry bushes stand near orchard or field, robins will be only too happy to dine on those berries and leave the cherries and blueberries to the farmer. The birds’ policing of insects, meanwhile, will still continue unabated.

In summary, then, we might characterize the robin’s relationship with cultivated crops as overridingly beneficial by virtue of the species’ continuous destruction of crop-consuming insects. And on those occasions where robins would indeed be significantly harmful to the farmer’s fruits—occasions that are frequently inspired by human actions—the birds can be either blocked or enticed away from the crops in lieu of being shot.

The Lawn Patrol

Just before robins lunge at a worm, they cock their head in the direction of their prey. This cocking movement has given many people, including early ornithologists, the natural impression that the birds are listening intently for faint sounds of earthworms moving within their burrows. Since most avian predators locate food by sight rather than sound, robins seemed in this respect a bit odd. It remained until only recently that scientists determined conclusively how robins actually find worms.

Possible cues that robins might employ in their hunting include vibrations (arising from the worm’s movements), odors, sounds and sights. Vibrations, however, were promptly ruled out by the observation that the heavy rumblings of nearby trucks and streetcars did not interfere with a redbreast’s lawn success. Worm odors also seemed unimportant since robins—like most birds—apparently have rather weak sniffers; in one of several tests, foul tidbits were presented to a captive robin who

nonchalantly ate foods smelling like rotten eggs, decaying meats, rancid butter, and the absolutely worst of all bad smells, mercaptoacetic acid, which has been described as a cross between sewer gas, rotten cabbage, a skunk and a stinkbug.

The potential role of hearing was then eliminated by the researchers when artificial background noise—noise loud enough to mask any possible sounds made by earthworms—did not stop robins from cocking their heads and finding their worms. Finally, vision was pinpointed as the crucial sense when dead worms that had been preserved in alcohol (and hence were vibrationless, odorless and soundless) were easily found and readily gobbled by unfinicky redbreasts. In conclusion, then, robins most assuredly see, and not feel, smell or hear the worm who drills its subterranean home beneath your lawn.

So why do robins so characteristically cock their head? Simple: Their eyes, being on the sides of their head, make it difficult to see close-range objects that are directly in front of them; they see better if objects are on their flank. So by turning and cocking their head, they are simply centering the visual field of one eye upon the target before launching their pouncing attack. Worms, incidentally, being ever prepared for hasty retreat, frequently catnap with only the tips of their bodies protruding from their tunnels. It is this tip o’ worm that robins must discover, focus upon, and grab with unerring accuracy.

Besides head-cocking, another striking characteristic of the hunting habits of robins is the zig-zag nature of their movements. First they’re running toward you, but then after a pause they’re off in an entirely different direction, and so on ad infinitum. Should multiple robins be simultaneously patrolling the same field, as indeed they often are, the resulting scene is that of a leaderless flock whose members can’t decide which way to proceed as they run hither and thither in apparent confusion. Actually, two separate factors largely determine the zany nature of these foraging movements.

The zig-zag business, first of all, is largely the product of ocular fixity. Since their eyes are virtually immovable within their respective sockets, robins must turn their whole heads to look in a given direction. Rather than rotate their heads a full quarter-turn—as would be necessary to look straight ahead—they just turn a little bit and, should the view be at all promising, promptly scamper off thataway. Then when they subsequently repeat the process, they may focus with the other eye and so embark upon an entirely different course.

A second factor affecting the robin’s lawn navigation involves the specific body orientations of nearby companions. Since the red breast seems to be an aggression-eliciting stimulus for the species, two birds who face each other head-on are likely to skirmish. Being more intent upon food than battle, robins try to dodge such confrontations during group feeding and so tend to avoid orienting breast-to-breast with each other. This avoidance of breasting thus imposes a restriction upon the direction of a robin’s movements; having spied worm signs in the distance, an individual will head off in that direction only if doing so will not bring him or her face to face with a conspecific. Of course, this antipathy toward breasting on community feeding grounds is not absolute. Robins do occasionally face each other and then fight, especially during early spring when hostility runs high. For the most part, however, such orientations are less frequent than they would be if movements were random.

Given the mutual antagonism that is at least potentially present during communal hunting, why do robins bother to gather on the same field in the first place? Why don’t they just avoid each other entirely and secure food outside of community cafeterias? For one thing, a flock of feeding robins has many watchful eyes to preclude surprise attacks by predators. Robins do have excellent group-warning signals, particularly in the form of loud calls that quickly send a foraging flock flapping for foliage. But robins periodically feed singly throughout the day (communal feeding occurs primarily during the early morning) and still manage to survive, so group protection would not seem to be the only selective advantage that encourages hunting in loose flocks.

In many birds, like soaring gulls or vultures, group feeding accrues real benefits since any discovery by one individual is quickly shared by all. But robins certainly do not share worms with each other and so “feeding efficiency” is not an obvious factor. This perplexing problem of robin sociability during a time when their spirits are generally spleenful will emerge again when we consider the roosting habits of redbreasts (Chapter 10). And unfortunately, a satisfactory resolution will be as evasive in that context as it is in the present one.

Before we close this chapter, sensitivity suggests that we embark upon an excursion of empathy and say a word about the worm. In their largely underground world, worms continuously work for environmental good and seem to cause little (though sometimes some) harm in the process. The earthworm, indeed, may be the single most important animal living in the soil. Tirelessly tilling the tough terrain, Lumbricus terrestris enriches the earth with excretions and aerates the land with burrows. Equally important, the earthworm is prey for a veritable menagerie of life ranging from microorganisms and insects through all the vertebrate families, including fish (ask any fisherman), amphibians (frogs and toads), reptiles (snakes and turtles), birds (an example escapes me), and a multiplicity of mammals (moles, shrews, skunks and armadillos, to name a few). Through enormity of number—Charles Darwin once estimated sixty-four thousand earthworms residing per acre—the annelid army brings as much as two inches of earth to the surface every ten years, a process invaluable to the health of the soil.

In addition to their ecological importance, earthworms have been major teachers in the science of anatomy, as any zoology student who’s ever held a scalpel will surely attest. Earthworms, furthermore, are intelligent. Well, at least they are not so dumb as their humble appearance would suggest. Worms seem able to learn, for example, which way to turn in a maze when a reward of moisture awaits them in the goal-box.

The point of all this is that every time we see a robin succeed in upping and downing a worm, we should realize that the episode represents not only the admirable execution of rare avian skill, but also the regrettable termination of one very fine animal. And the robin would be the first to tell you so.