The results of research conducted by University of Florida biologist Doug Levy suggest that it appears northern mockingbirds can indeed differentiate between certain people.
In a simple experiment that could have been conducted in any yard where mockingbirds are nesting, Levy instructed a research assistant to walk up and touch an active nest four consecutive days in a row. The researcher discovered the nesting pair was slow to react to the individual on the first day. However, they became agitated more quickly when this large potential predator approached their nest each day thereafter.
Then, on the fifth day, when a different person approached the nest, he noted the birds became alarmed just a slowly as they did when the first interloper touched the nest for the first time.
He concluded the mockingbirds quite possibly recognized the differences between the first and second research assistants. It also suggests that this ability helps this popular backyard bird survive close to people.
Perhaps this helps explain why mockingbirds we routinely see in our yards on a regular basis allow us to approach them more closely than they do strangers.