 European
starlings are prodigious singers. Virtuosos of the treetop world,
they produce some of the longest and most complex bouts of birdsong.
They’re also expert mimics, picking up and adding to their
repertoires from car alarms and squeaky doors to human speech and
vocalizations of other species. But could these three-ounce birds
also pose a challenge to language heavyweight Noam Chomsky?
The answer, it seems, is “yes.”
In a study published in Nature, Tim Gentner,
of the UCSD psychology department, and colleagues from the University
of Chicago demonstrate
that starlings
can learn simple recursive grammar patterns—of the kind thought
to be
the exclusive province of humans.
“Recursion” refers to the common characteristic of human grammar
that
allows for the creation of new utterances by inserting words and
clauses within
sentences. Chomskian linguists have held not only that this is a
universal feature of human language but also that the ability
to process it forms the computational core of a uniquely human language
facility.
Gentner and his co-authors used recordings of different starling “warbles” and “rattles” to
create artificial songs that followed two different rules: one that
allowed for sounds to be inserted in the middle of an acoustic string
and is the simplest form of recursion; and another that allowed sounds
to be appended only at the beginning or end of a string and was thought
to account for all nonhuman communication. Eleven adult birds were then taught to distinguish between the
two sets of songs using classic reinforcement techniques. After
10,000
to 50,000 trials over several months, nine of the starlings eventually
learned to distinguish the patterns.
When tested with different paired combinations of rattles and warbles
that either followed the same rules or violated them, the starlings
performed well above chance, suggesting they had learned the abstract
patterns and not just memorized the
specific songs. The experimenters then asked if
the birds were capable of a key feature of human grammars: Could
the starlings
extrapolate these rules to longer sequences, of three and four
rattle/warble combinations? Remarkably, Gentner
says, they could. The finding that starlings can grasp even these simple rules, Gentner
says, suggests that humans and other animals share basic levels of
pattern recognition and also hints at the likelihood of other cognitive
abilities we have in common.
More generally, “The more closely we understand what nonhuman
animals are capable of,” Gentner says, “the richer our
world becomes.”  — Inga Kiderra
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