Response to intruder number is related to spontaneous 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 utilized to detect such abilities in animals; cognitive tasks in which individuals must choose between two quantities of food, and playback experiments of the vocalizations 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 (1) selected the greater quantity of food in the cognitive task and (2) responded more strongly to 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 behaviors, as this has the potential to offer profound insights into cognitive ecology.