Waterbird solves the cognitive string-pull test

String-pulling is amongst the most widespread cognitive tasks used to test
problem-solving skills in mammals and birds. The task requires animals to
comprehend that pulling on a non-valuable string moves an otherwise
inaccessible food reward to within their reach. Although at least 90 avian
species have been administered the string-pull test, all but five of them
were perching birds (passeriformes) or parrots (psittaciformes).
Waterbirds (Aequorlitornithes) are poorly represented in the cognitive
literature, yet are known to engage in complex foraging behaviours. In
this study, we tested whether free-living ring-billed gulls (Larus
delawarensis), a species known for their behavioural flexibility and
foraging innovativeness, could solve a horizontal string-pull test. Here,
we show that 25% (26/104) of the ring-billed gulls that attempted to solve
the test at least once over a maximum of three trials were successful, and
that 21% of them (22/104) succeeded during their first attempt.
Ring-billed gulls are thus the first waterbird known to solve a horizontal
single-string-rewarded string-pull test. Since innovation rate and
problem-solving are associated with species’ ability to endure
environmental alterations, we suggest that testing the problem-solving
skills of other species facing environmental challenges will inform us of
their vulnerability in a rapidly changing world.