Fig. 2

The daily success rate of the turtles in the fixed numerosity tests (Experiment 1). Each numerosity pair was tested 20 times per day on each of the five turtles for five days. The entire experiment lasted 25 days, starting from the lowest ratio (1 versus 3, ratio = 0.33, day 1–5) to the highest ratio (6 versus 7, ratio = 0.85, day 21–25) including two transfer tests and one conflict test. The solid lines with shaded areas are predicted mean probabilities of success ± 1 standard error, estimated from the best-fit model (Table 2 & Additional file 1: Table S2). The horizontal dashed line denotes random choice of the smaller and larger quantity