Capabilities for long-term memory and recall of information have evolved
in non-human animals primarily for special requirements such as for
learning species-typical vocalizations and caching food. Long-term memory
of individual social partners has, however, not been demonstrated
previously for non-human animals.
The ability to recognize individuals has important consequences for the
evolution of intricate social interactions and provides a basis for more
sophisticated forms of cognition in animal societies. Recognition of
social partners has been documented for territorial songbirds, which
discriminate between songs of different neighbours as well as between the
songs of strangers and neighbours.
Here I show that male hooded warblers (Wilsonia citrina),
Parulinae) not only recognize their neighbours individually by song during
the breeding season, but also retain the memory of neighbours' songs after
an 8-month period during which they cease singing and migrate to Central
America before they return to former breeding territories.