From Chapter Six
The most famous example of "collective drunkenness" in birds is that of American robins during their annual February migration to California, and in particular to the small town of Pleasant Hill. The amazing behavior of these birds on their arrival first made news in the 1930s.
Once they reach California, flocks of thousands of robins (the species Turdus migratorius) perch on small ornamental trees popularly known as California holly, though the Native Americans of the region call this scarlet fruit toyon. At this time of year the trees are laden with scarlet fruits called Christmas or holly berries. The robins, and other kinds of birds as well, gorge themselves on these fruits, bingeing until they are blatantly drunk. For about three weeks this region unintentionally hosts what can only be called a drunken orgy on the part of the birds, who become disoriented and confused, engaging in silly games with each other and fluttering wildly into cars and houses.
Ronald K. Siegel, who has studied this phenomenon with great attention, notes that although four or five holly berries would suffice to make a full meal, a single robin will gobble down as many as thirty at a time. Clearly the purpose of such gorging transcends simple nutrition; it would seem conclusive that the birds recognize and remember the fruit and seek out the intoxication induced by eating massive doses of it. In his book Intoxication: Life in Pursuit of Artificial Paradise, Siegel describes the behavior of a flock of about three thousand American robins after their arrival in Pleasant Hill. Excerpts from his observations follow.
"They quickly work their way to the outermost branches which begin to sag under their collective weight. As the branches wobble, so do the birds and they [the birds] start falling. Four birds are staggering on the ground, unable to fly. . . . [Now] there are eighteen birds on the ground. Several are still grasping berries in their beaks. A lone starling pilfers a berry right out of the locked beak of a robin. . . . A group of birds on the start of another feeding frenzy flies directly into my head and body. . . . I am driving in low gear to the edge of the field. There are thumps against the roof, then a robin smashes into the windshield. . . . Several birds are stunned momentarily when they fly into the windows and sides of houses. On the side of the road I find four more birds that have been killed in collisions with cars. . . . I performed autopsies on the dead birds. [They] revealed that the stomach, and sometimes the throat, of every bird was full of toyon berries, accounting for approximately 5 percent of their total body weight. Neither the stomach contents nor the berries themselves showed evidence of fermentation or alcohol. . . . Death was caused by a massive trauma inflicted by the collisions, secondary to an unknown intoxication" (Siegel 1989, 58-59).
Apparently, then, there have been no true cases of overdose in the robins and other birds who get high on the holly berries, and the only fatalities?very few, statistically speaking?are due to the presence of human beings: their cars, windows, and random acts of brutality. The local press, which almost every year dedicates a paragraph or two to the bizarre behavior of the migrating robins, frequently refers to the deaths of birds who have flown into cars or houses as "suicides," a misnomer and completely erroneous interpretation of the facts.
During the same time period and in the same region of California, birds become intoxicated on the fruits of yet another shrub, Pyracantha, a member of the rose family popularly known as firethorn. In this case, the birds act "like winged clowns: flying, falling, and hopping about in the most erratic, albeit entertaining, ways. Some were found fluttering in the dirt with wings awry, teasing backyard cats. Others teetered on window ledges and pecked at their reflections. Because firethorns were often planted near homes and roads, collisions with windows and cars were reported more frequently than with toyon" (Siegel 1989, 60).
The bark of the toyon tree was used by the Native tribes of California for tanning, while its fruits were roasted and eaten or brewed to make an intoxicating cider. However, it is not yet known precisely which substances in these sour, scarlet fruits are responsible for their inebriant effects on birds or humans, who have sometimes experienced delirium and visions after drinking toyon cider. Possibly they are due to the presence of psychoactive saponins, since another case of collective "drunken" bird binges hinges on Tartarian honeysuckle, a source of similar saponins. Tartarian honeysuckle, Lonicera tatarica, is a shrub native to Asia but widely cultivated along the eastern coast of the United States. In this case as well, robins are the birds most attracted by its intoxicating berries.
In 1926 J. Grinnell observed the behavior of these birds in his garden: "There were dozens of robins on the bushes and everywhere on the ground. They appeared tame and dazed. Some lay on the earth in the dirt with their wings awry. I regretted the fact that their condition rendered the birds unusually easy to catch by our cat, who seemed to know very well that he could catch one any time he felt like it." This avian disruption peaks in June, when the plant's berries are ripest and most colorful.