Mind Altering Animals
Biology 342 Fall 2014
Adaptive, Mind-opening, or a Waste of Time?
Many species of birds, namely robins, feed on small red berries such as “Firethorn” or “Pyracantha” berries and Holly berries. In Ronald K. Siegel’s book Intoxication:Life in Pursuit of Artificial Paradise, he details the birds glutinous behavior, how they “work[ed] their way to the outermost branches [of the pyracantha tree] which beg[an] to sag under their collective weight [and] as the branches wobble[d], so [did] the birds,” until they tumbled to the ground. These berries are alcoholic when ripened and birds often fly into things after consumption. Researchers in california found (from studying birds killed by flying into windshields) that robins can have up to 50 berries or more in their stomachs at once, each berry contaning an average of 800 ppm of ethanol.
Clearly, the consumption of these berries seems to threaten the reproductive fitness of robins. Why then do they continue to eat the berries in such great numbers?
Figure 1. Cedar waxwing robin eating a pyracantha berry
Many find it appealing to dismiss the birds as drunks who can’t kick the habit. One article advised that, upon seeing an especially drunk bird, one should “place it in a well-ventilated box, and put that in a dark, quiet place,” one almost expects the author to recommend the administration of ibuprofen and a cold shower the next morning, perhaps even a thimble sized bloody mary. However, this interpretation doesn’t account for the persistence of this behavior in the population, especially considering the relationship between robbins and holly berries has remained stable for a very long time.
Clearly this behavior confers a cost to the robins- those that consume the alcoholic berry are more likely to die from a collision with a car windshield, or get eaten by predators. So, considering the persistence of the aforementioned behavior, what benefits do the robins receive that are substantial enough to overwhelm the negative costs incurred? Samorini might argue the alteration of consciousness is pay-off enough, alcohol has been know to increase creativity in humans, why not birds too? Just imagine it, an avian Ernest Hemingway, or maybe a F. Scott Fitzgerald.
If hypothesized that these birds consume berries for their alcohol content, due to its indicative nature of nutrition, and because they are severely lacking in nutrition due to their migration, it could be tested by providing other food sources that have alcohol in them such as blueberries or cherries (common robin foods) which have been soaked in alcohol. The selection preference could then be compared for the more alcoholic fruit or the less alcoholic pyracantha berries. If our hypothesis is that these birds gorge on berries due to being voraciously hungry from migration, we would expect these birds to opt for the pyracantha, associating nutrition with the berries. If however the bird were selectively looking for alcohol content, we would expect the first few choices between foods to be arbitrary, but eventually the bird would learn that the alcohol soaked cherries contain a higher alcohol content and choose those over pyracantha berries.