Results of four additional map assay experiments, in which turtles discriminated between a magnetic field in which they were fed and a magnetic field in which they were not a–d, Turtles differentiated between magnetic fields that exist near: Delaware, USA, and Cuba (a; two-tailed Wilcoxon signed-rank test, w = 108, P = 0.04, Hedge’s g = 0.50, n = 16); Maine and Florida, USA (b; two-tailed Wilcoxon signed-rank test, w = 121, P = 0.004, Hedge’s g = 0.63, n = 16); Newfoundland, Canada and Virginia, USA (c; two-tailed Wilcoxon signed-rank test, w = 115, P = 0.01, Hedge’s g = 0.60, n = 16); and the Turks and Caicos Islands and Haiti (d; two-tailed Wilcoxon signed-rank test, w = 97, P = 0.003, Hedge’s g = 0.60, n = 14). The data in c represent a second conditioning experiment conducted with the same turtles used in b and thus indicate that turtles can learn magnetic fields that exist at multiple locations. Remaining conventions are as in Fig. 1. Extended Data Fig. 2 shows the same data plotted on a linear scale. The maps were created using Natural Earth (https://www.naturalearthdata.com; credit Tom Patterson and Nathaniel Vaughn Kelso). Source data