The bird in the mirror
This week’s paper is “Mirror-induced behavior in the magpie (Pica pica): evidence of self-recognition?, by Helmut Prior and colleagues, available online in PLoS Biology.
When confronted with mirrors, apes (including humans) react very differently from monkeys. Monkeys never seem to recognize that they are seeing a reflection of themselves rather than another monkey. Recently, dolphins and elephants have been added to the list of species that can recognize themselves in mirrors and use them for self-exploration. Most other species can not. Is this because their brains are too small? Or is the tendency to self-exploration using a mirror a side-effect of a mental ability that evolved for other reasons? If the latter is true (even if there is also some minimum brain size requirement), then more species that need to pay more attention to what others of their species are doing might be more likely to evolve this mental ability.
Some birds, for example, hide food, raid each other’s food caches, and pay attention to who was around when they were hiding food. How do these birds respond to mirrors?
Prior’s group tested five individual magpies. All initially responded to the mirror as if it were another bird, but three changed their behavior and appeared to be examining themselves, like apes, dolphins or elephants. The most convincing test involved marking the birds somewhere they could see in the mirror but not directly. Two of the three birds that examined themselves in the mirror paid increased attention to a yellow mark but not to a black control mark (invisible against their feathers). They even removed the mark, as seen a video available online.
So some magpies show behaviors previously seen only in species with larger brains. This was not true of all individuals, consistent with results for some other species. What can explain this difference among individuals? Are there genetic differences in this trait? I wouldn’t expect individuals to vary genetically in traits that are consistently beneficial, but many behavioral traits are beneficial under some conditions and not others. Or is there some difference in experience among individual birds that makes them less curious or in some sense less intelligent?