Claw-in-the-door: pigeons, like humans, display the foot-in-the-door effect

People are more likely to comply with a large request when it is preceded by another, smaller request, and this is known as the "foot-in-the-door" (FITD). The FITD has been widely studied in social psychology and is thought to arise from mutually conflicting beliefs about past and present behavior (cognitive dissonance) or changes in self-perception. Across two experiments, we found that pigeons' latency to respond to an effortful second stimulus in a pair scales with how much effort they had exerted on the first stimulus. As such, pigeons also display a FITD-like effect. We argue that the FITD may not be caused by conflicting beliefs or changes in self-perception but may instead be the product of behavioral contrast.