A University of Florida study has demonstrated that Northern Mockingbirds can distinguish individual humans and respond to them based on whether they’ve previously been threatened by that specific human. In the study, grad students who poked at Mockingbird nests on consecutive days were subsequently hassled by the parent Mockingbirds, while grad students who had not poked the nest were allowed to approach much closer without being dive-bombed, shrieked at, or otherwise subjected to Mockingbird ire.

This is a remarkable ability for a bird with a brain maybe the size of a large honey-roasted cashew, and the researchers speculate that it may have contributed to the Mockingbird’s success in colonizing urban and suburban landscapes. Understanding which factors lead to the success of urban-dwelling birds is not only nifty in its own right, it can potentially offer clues on how to make urban and suburban habitats more congenial to less flexible species.

It’s a fascinating study, and the more I think about it, the more questions it raises. How do the mockingbirds do it? The grad students wore different clothes on different days of the experiment, so it’s not based on “plumage”. Either the birds can recognize distinct human faces/hair colors, etc., or it’s something more subtle, like gait or the timbre of the individual voice (Mockingbirds are, after all, quite good at noticing and remembering sounds).

And why? Has urbanization been around long enough to be a major selective pressure on Mockingbirds? Or is this a pre-existing trait now being adapted to a novel environment? And if so, what was it used for before people, with their puzzling propensity to poke nests, came along? It seems to me that once most predators know where your nest is, there’s not much left to defend for next time, so it’s better to go after all of them, not just memorable individuals – but I’m not a Mockingbird, so I could be wrong. Maybe preemptive aggression towards predators that don’t already know where the nest is only tips them off that there’s something interesting in the neighborhood.

Or perhaps this behavior drives away clumsy herbivores that might disturb or expose, not devour, the nest – say by preventing the local deer from making a particular shrub a regular snack-bar stop. In that case, it would be a waste of resources to hassle a deer that was just passing through.

Obviously, all this is just speculation and much further study is needed, which just goes to show that even common birds are worth careful observation. After all, it appears that they’re carefully observing us!

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