I wrote about birds and mirrors a while ago, and not much has changed scientifically since then. Most bird species tested have interpreted their own reflections as other individuals, responding either with aggression or courtship. Female pigeons who view their own reflections ovulate, apparently interpreting their reflections as suitable mates. Among birds, only magpies, so far, have been demonstrated to understand that the mirror reflects their own image, although pigeons can be trained to use spatial information from mirrors correctly in the real world.
So why bring this up again? Recently I saw a Yellow-rumped Warbler interacting with its reflection in a car side mirror, and took a video with my phone. Here it is (apologies for the lack of zoom):
At the time I took the video, I didn’t think much of it beyond general amusement. But rewatching it, I began to have some questions.
If the warbler interprets the reflection as another warbler, why does it attack? In the breeding season, another bird might merit some aggression, but it’s winter flock season here; the warbler was in a flock of other yellow-rumps at the time, and certainly did not respond to every glimpse of its flockmates with an attack. And why does the warbler keep going back to the mirror? It can’t see the reflection when it is perched on the mirror, as it is after each attack; it could easily interpret the vanishing of its opponent as the opponent’s having fled, and leave victorious. It can’t be going back to the mirror out of loneliness; the tree directly above it is chirping full of its fellows.
Some birds, given an option between a mirror and a view of an actual other live individual, prefer the mirror; the researchers suggested that this is because the mirror-bird’s behavior is predictable, but I wonder if there isn’t more going on here. We know most birds don’t understand mirrors—but perhaps they do understand that there is something off about them. The warbler in the video looks around after each scuffle with its reflection, as if looking for the mirror bird. Could the birds’ preference for their reflections—the warbler’s repeated returns to the mirror—be curiosity? A desire to return to a stimulus that doesn’t match the animal’s previous experience, and figure it out?
Clearly, a single warbler video does not a dataset make, and I’m not currently in a position to test any of this properly. But I’m going to pay more attention now to any birds I see interacting with their reflections. If you’ve ever seen a bird with a mirror, let me know in the comments what you think.
Derégnaucourt S, Bovet D. 2016. The perception of self in birds. Neuroscience & Biobehavioral Reviews 69:1-14.