By Amit and Dan Ariely

For the past few weeks, my 8-year old son Amit and I have been observing birds, paying attention to their individual and particular behavior.  We noticed that some of the birds we observed were different in their physical characteristics like color, shape and size, and that these traits varied with their behavior. This made us wonder about the possible evolutionary links between the appearance of the birds on one hand and their respective behavior on the other.

The first difference that stood out to us was between the small and large red birds. Although the larger ones were about twice as big, their ability to fly was about the same — but what was very different about the two kinds was that the larger red birds were much more aggressive and caused more damage when they attacked. Of course, the evolutionary reason for this difference in aggression seems straightforward; as the subtype of birds gets larger, they need more food, and with this increased requirement, aggression becomes an important survival skill.

The yellow subtype of birds were slightly more of a challenge to figure out. Other than being yellow, their general characteristics were similar to the red birds — but Amit and I couldn’t help but notice their tendency to suddenly fly at much higher speeds relative to the red birds. We speculated that the evolutionary reason for this difference must be that the red birds, by virtue of their threatening color, are less appealing to predators, and as a consequence they never needed to develop enhanced speed to escape. In contrast, the yellow birds practically invite predators to dine with their appealing color. With this clear disadvantage the yellow birds are forced to rely on an alternative survival mechanism, in this case the valuable skill of speed.

Another interesting feature of the yellow bird is that it is sharper, perhaps because it is a species connected with the woodpecker family.  The yellow birds’ sharpness might also help it further when it needs to break down a structure or cut through wood – which again is most likely connected to their need to compensate for their color disadvantage.

The blue birds were fascinating in their ability to self-replicate, and in all of the cases we observed they produced exactly three offspring. We wondered why the blue birds evolved to produce offspring at such speed and timely consistency, and we determined that the evolutionary reason for this must be that because the blue birds are small and relatively slow, they had to develop a skill for efficient reproduction, thereby hedging their bets and increasing the potential to pass on their genes.

The white birds were even more puzzling. On multiple occasions, we watched them drop their eggs while still in flight, naturally crushing the egg. Initially this seemed to be a counter-evolutionary strategy, but once we inspected the discarded eggs we realized that these eggs were abnormal, and it was probably the white bird’s strategy for dealing with eggs that have a low potential for survival. One additional observation in support of this hypothesis is that the white birds seemed to be much healthier, lighter and happier after the eggs were discarded.

Of course there were many other birds as well, including one particularly interesting black bird, and Amit and I are thinking of continuing to pursue this bird-project for a while. In fact, we are already getting somewhat addicted to it, and we just learned that there are plenty more birds to observe in Rio.

But what really baffles us is this: why are these birds SO angry?

Amit and Dan