-Previous reports suggest that pigeons are highly sensitive to speed of motion (Cook, Beale, Koban, 2011;Herbranson, Fremouw, & Shimp, 2002). In contrast, we found that pigeons required more extensive training to learn speed discrimination than size discrimination (Lazareva, Young, & Wasserman, 2014). However, our results were based on a comparison of two experiments conducted in different laboratories, complicating the interpretation of the data. Here, we trained pigeons to perform size discrimination or speed discrimination in a two-alternative simultaneous discrimination task using a within-subject design. All birds acquired size discrimination much faster than speed discrimination, confirming our prior report. We further explored pigeons' sensitivity to differences in speed and size by training them to discriminate two end-point stimuli in a two-alternative forced-choice task and then presenting a wide range of testing stimuli located between the training end-point stimuli. The results again indicated weaker control by the differences in speed in comparison to size; comparable results were obtained for human participants.