Response to intruder number is related to quantity discrimination performance in a wild bird

Quantity discrimination abilities are considered a valuable skill for many
aspects of life, including foraging, predator avoidance, and intergroup
contests. Two types of experiments are often utilised to detect such
abilities in animals: cognitive tasks in which individuals must choose
between two quantities of food, and playback experiments of the
vocalisations of differing numbers of intruding individuals. To date, no
study has investigated whether individual performance in these two types
of experiments is related. We presented wild Western Australian magpies
(Gymnorhina tibicen dorsalis) with both a spontaneous quantity
discrimination cognitive task and a playback experiment, to investigate
quantity discrimination abilities, and to explore if performance on these
experiments is related. We found that magpies (a) selected the greater
quantity of food in the cognitive task and (b) responded more strongly to
the playback of three callers compared to one caller, suggesting this
species possesses quantity discrimination abilities. Individual
performance on these two experiments was negatively correlated, with
magpies that performed better on the cognitive task spending less time
vigilant following the three-caller playback compared to magpies that
performed worse. Our results highlight the importance of exploring the
relationship between performance in a cognitive task and ecologically
relevant behaviours, as this has the potential to offer profound insights
into cognitive ecology.